Diseases and Pathogens of Eucalypts

D i s e a s e s a n d Pa t h o g e n s o f

EUCALYPTS

Dedication This book is dedicated to the memory of Dr Geoffrey Charles Marks (1932–90) who, after 27 years of experience as a Forest Pathologist with the Victorian Government and as a teacher of Forest Pathology at the University of Melbourne, saw the need for such a book. He initiated its writing and undertook the initial planning of its structure and authorship. Geoff was born in Sri Lanka (formerly Ceylon) and was an outstanding athlete and scholar, representing his country as a swimmer at the Helsinki Olympics and completing an honours degree in science at the University of Ceylon, followed by an MSc (1961) and PhD (1963) while on a Rockefeller Foundation Scholarship at the University of Wisconsin. He took up his appointment with the then Forests Commission of Victoria in Melbourne in 1963 and thereafter was involved in the study of eucalypt diseases, being a central participant in the initial studies of dieback caused by Phytophthora cinnamomi in Victorian eucalypt forests. He also initiated early studies on the eucalypt leaf pathogen, Mycosphaerella, in southern Australia. His keen intellect, enlightened attitudes, great enthusiasm and curiosity, waspish good humour and propensity to provoke critical discussion inspired colleagues and led to fruitful collaborations with many people. He developed a deep appreciation of the eucalypt forests of his adopted country, and from this grew his keen understanding of their ecology and pathology. He conducted wide ranging field studies on many aspects of forest pathology and greatly enjoyed field trips to investigate disease problems in the diverse forests of Victoria, tirelessly speculating about the complex causes of the diseases and planning experimental studies with whomever was fortunate enough to accompany him. While returning home from one of these long trips to the forests of eastern Victoria he was seriously injured in a car accident. He showed great courage in recovery, and never lost his enthusiasm, expressed at the time by his delight in initiating and planning this book. He was not destined to see this work to fruition as he died suddenly in August 1990. Vale, Geoff. We hope this book has not fallen too far short of your vision.

Title

D i s e a s e s a n d Pa t h o g e n s o f

EUCALYPTS

P. J. Keane, G. A. Kile, F. D. Podger and B. N. Brown (Editors)

© CSIRO 2000 All rights reserved. Except under the conditions described in the Australian Copyright Act 1968 and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, duplicating or otherwise, without the prior permission of the copyright owner. Contact CSIRO PUBLISHING for all permission requests. National Library of Australia Cataloguing-in-Publication entry Diseases and pathogens of eucalypts. Bibliography. Includes index. ISBN 0 643 06523 7 (paperback). ISBN 0 643 09012 6 (eBook). 1. Eucalyptus – Diseases and pests – Australia. I. Keane, Philip J. 634.9737660994 This book is available from: CSIRO PUBLISHING

PO Box 1139 (150 Oxford Street) Collingwood VIC 3066 Australia Tel: (03) 9662 7666 Int: +(613) 9662 7666 Fax: (03) 9662 7555 Int: +(613) 9662 7555 Email: [email protected] http://www.publish.csiro.au Typeset by Desktop Concepts P/L, Melbourne Printed in Australia by Brown Prior Anderson Cover photographs Upper: Crown decline typical of that observed in trees of Eucalyptus obliqua and E. regnans affected by regrowth dieback and Armillaria. Lower: Crinkle leaf caused by Mycosphaerella cryptica on tip leaves of a seedling of Eucalyptus obliqua. Publication of this book was supported by a grant from the Standing Committee on Forestry of the Australian Ministerial Council on Forestry, Fisheries and Aquaculture.

C O N T E N T S

Preface Contributors

xiii xvi

Section I: The Eucalypts—Their Importance, Diversity and Biology 1

Economic and Social Importance of Eucalypts

1

J.W. Turnbull

2

Summary

1

1.1

Introduction

2

1.2

Eucalypts in native forests

2

1.3

Eucalypts as exotics

3

1.4

Industrial eucalypt plantations

4

1.5

Eucalypts in the rural landscape

5

1.6

Conclusion

7

1.7

References

7

Morphology, Phylogeny, Origin, Distribution and Genetic Diversity of the Eucalypts

11

B.M. Potts and L.A. Pederick Summary

11

2.1

Introduction

12

2.2

Morphology

12

2.3

Phylogeny

14

2.4

Origins

16

2.5

Distribution

18

2.6

Hybridisation

21

2.7

Genetic variation

23

2.8

Genetic variation in susceptibility to disease

24

2.9

Factors affecting disease risk in plantations

26

2.10

Acknowledgments

27

2.11

References

27

v

D I S E A S E S

3

A N D

P A T H O G E N S

O F

E U C A L Y P T S

Growth Habits and Silviculture of Eucalypts

35

R.G. Florence

4

Summary

35

3.1

Introduction

36

3.2

Growth habits of the eucalypts

36

3.3

Sivicultural practice in natural forests

38

3.4

Ecologically sustainable silviculture

40

3.5

New directions in silviculture

42

3.6

Eucalypt plantations

43

3.7

Conclusion

44

3.8

References

44

Ecology of Eucalypt Regeneration

47

D.H. Ashton

5

Summary

47

4.1

Introduction

48

4.2

Characteristics of eucalypts in relation to their regeneration

50

4.3

Conditions required for regeneration

51

4.4

Major modes of regeneration

51

4.5

In synthesis—the strategies of survival

58

4.6

References

59

Physiology of Eucalypts in Relation to Disease

61

C.L. Beadle

6

Summary

61

5.1

Introduction

62

5.2

Productivity and light interception

62

5.3

Biomass production, partitioning of dry mass and foliage

63

5.4

Gas exchange and stomatal conductance

64

5.5

Water relations

66

5.6

Conclusion

68

5.7

References

68

Mycorrhizas of Eucalypts

71

G.A. Chilvers

vi

Summary

71

6.1

Introduction

72

6.2

Structure of eucalypt mycorrhizas

73

6.3

Functioning of mycorrhizas

74

6.4

The fungal partners of eucalypts

83

6.5

Mycorrhizal infection cycles

86

6.6

Ecology of mycorrhizas

87

6.7

Manipulating eucalypt mycorrhizas

90

6.8

References

94

C O N T E N T S

Section II: The Diseases of Eucalypts—Their Causes and Biology 7

Diseases and Fungi of the Reproductive Structures of Eucalypts

103

B.N. Brown

8

Summary 7.1 Introduction 7.2 Fungi of flowers and capsules and their pathogenicity 7.3 Seed fungi of eucalypts 7.4 Control of seed fungi 7.5 Conclusion 7.6 References

103 104 104 106 114 115 115

Disease during Propagation of Eucalypts

119

B.N. Brown and F.A. Ferreira

9

Summary 8.1 Introduction 8.2 Diseases with abiotic causes 8.3 Fungal diseases 8.4 Principal diseases of eucalypt cuttings 8.5 Conclusion 8.6 References

119 120 120 121 143 143 143

Fungal Diseases of Eucalypt Foliage

153

R.F. Park, P.J. Keane, M.J. Wingfield and P.W. Crous

10

Summary 9.1 Introduction 9.2 Target spot (Aulographina eucalypti) 9.3 Leaf spot, leaf blotch and crinkle leaf blight (Mycosphaerella species) 9.4 Biotrophic infections 9.5 Powdery mildews (Oidium species) 9.6 Eucalypt rust (Puccinia psidii) 9.7 Angular, vein-limited leaf spots 9.8 White leaf and shoot blight (Sporothrix pitereka ) 9.9 Winter leaf spot (Piggotia substellata and Ceuthospora innumera) 9.10 Leaf spots and speckles of minor importance 9.11 Leaf spots and blights of stressed plants 9.12 Conclusion 9.13 Acknowledgments 9.14 References

153 154 155 163 175 191 191 193 206 206 210 218 227 230 230

Canker Diseases of Eucalypts

241

K.M. Old and E.M. Davison Summary 10.1 Introduction 10.2 Fungal invasion and host responses 10.3 Effect of plant stress on the development of cankers 10.4 Major canker diseases of eucalypts

241 242 242 244 245

vii

D I S E A S E S

10.5 10.6 10.7 10.8

11

A N D

P A T H O G E N S

O F

E U C A L Y P T S

Opportunistic pathogens associated with cankers in eucalypts Conclusion Acknowledgments References

Diseases of Eucalypts Caused by Soilborne Species of Phytophthora and Pythium

248 252 252 253

259

B.L. Shearer and I.W. Smith

12

Summary 11.1 Introduction 11.2 Origin of the pathogens 11.3 Host range 11.4 Distribution patterns and effect of disease 11.5 Host–pathogen interactions 11.6 Pathogenicity of Pythiaceae on eucalypts 11.7 Effects of disease on wood production and conservation values 11.8 Pathogen dynamics 11.9 Resistance mechanisms 11.10 Effects of environment on disease development in established infections 11.11 Conclusion 11.12 Acknowledgment 11.13 References

259 260 261 261 262 264 267 269 272 280 282 284 284 284

Woody Root Rots of Eucalypts

293

G.A. Kile

13

Summary 12.1 Introduction 12.2 Armillaria root disease 12.3 Pseudophaeolus root disease 12.4 Ganoderma root rot 12.5 Other woody root diseases 12.6 Conclusion 12.7 References

293 294 294 300 301 301 302 303

Stem and Butt Rot of Eucalypts

307

G.A. Kile and G.C. Johnson Summary 13.1 Introduction 13.2 Causal organisms and hosts 13.3 The decay process 13.4 Factors affecting decay development 13.5 Particular heart rots and stem conditions 13.6 Conclusion 13.7 Acknowledgments 13.8 References

viii

307 308 308 323 327 331 332 333 333

C O N T E N T S

14

Diseases of Eucalypts Associated with Viruses, Phytoplasmas, Bacteria and Nematodes

339

T.J. Wardlaw, G.A. Kile and J.C. Dianese Summary 14.1 Introduction 14.2 Virus-like diseases 14.3 Diseases associated with phytoplasmas 14.4 Diseases caused by bacteria 14.5 Diseases associated with nematodes 14.6 Conclusion 14.7 References

15

Mistletoes and other Phanerogams Parasitic on Eucalypts

339 340 340 341 343 346 348 349

353

N. Reid and Z. Yan Summary 15.1 Introduction 15.2 Mistletoes parasitic on eucalypts 15.3 Native cherries parasitic on eucalypts 15.4 Dodder-laurels parasitic on eucalypts 15.5 Acknowledgments 15.6 References

16

Nutritional Disorders and other Abiotic Stresses of Eucalypts

353 354 354 375 377 378 378

385

P. Snowdon

17

Summary 16.1 Introduction 16.2 Diagnosis 16.3 Nutrient deficiencies 16.4 Toxicities 16.5 Water as an abiotic factor 16.6 Frost 16.7 Artificial environments 16.8 Miscellaneous abnormalities 16.9 Conclusion 16.10 References

385 386 386 386 395 398 400 401 402 402 403

Eucalypt Diseases of Complex Etiology

411

K.M. Old Summary 17.1 Introduction 17.2 Etiology of diebacks and declines 17.3 Diebacks of native forests and woodlands 17.4 Forest diebacks associated with drought 17.5 Forest diebacks associated with successional changes 17.6 Forest and woodland diebacks associated with chronic insect herbivory 17.7 Plantation diseases of complex etiology

411 412 412 414 414 416 416 421

ix

D I S E A S E S

17.8 17.9

A N D

P A T H O G E N S

O F

E U C A L Y P T S

Conclusion References

422 423

Colour Plates Section III: Management of Eucalypt Diseases 18

Management of Eucalypt Diseases—Options and Constraints

427

J.A. Simpson and F.D. Podger Summary 18.1 Introduction 18.2 Environmental concerns 18.3 Quarantine and eradication 18.4 Forest health surveillance 18.5 Approaches to disease management 18.6 Political and legislative considerations 18.7 Conclusion 18.8 Acknowledgments 18.9 References

19

Management of Disease in Native Eucalypt Forests and Woodlands

427 428 430 431 432 433 438 439 440 440

445

F.D. Podger and P.J. Keane

20

Summary 19.1 Introduction 19.2 Management of dieback caused by Phytophthora cinnamomi 19.3 Management of dieback diseases of complex etiology 19.4 Management of root rot caused by Armillaria luteobubalina 19.5 Management of foliar and canker diseases 19.6 Management of stem and butt rots 19.7 Conclusion 19.8 Acknowledgments 19.8 References

445 446 449 460 464 466 467 469 470 470

Management of Phytophthora cinnamomi during Bauxite Mining in Eucalyptus marginata Forest—A Special Case

477

I.J. Colquhoun and P.E. Elliott Summary 20.1 Introduction 20.2 The mining operation 20.3 Objectives of rehabilitation and the dieback management program 20.4 The management strategy 20.5 Procedures for disease control 20.6 Success in management of disease 20.7 Conclusion 20.8 References

x

477 478 478 479 479 481 483 485 485

C O N T E N T S

21

Management of Disease during Eucalypt Propagation

487

B.N. Brown Summary 21.1 Management of nursery diseases—general principles 21.2 Two minimal-disease nursery systems 21.3 Control of particular nursery diseases 21.4 Control of principal diseases of eucalypt cutting programs 21.5 Conclusion 21.6 Acknowledgments 21.7 References

22

Management of Disease in Eucalypt Plantations

487 488 491 493 510 510 511 511

519

P.D. Gadgil, T.J. Wardlaw, F.A. Ferreira, J.K. Sharma, M.A. Dick, M.J. Wingfield and P.W. Crous Summary 22.1 Introduction 22.2 Disease and the selection of species 22.3 Disease management strategies 22.4 Conclusion 22.5 Acknowledgments 22.6 References

Animal Index Birds and Mammals Scientific Names Birds and Mammals Common Names Insects Nematodes

519 520 520 523 527 527 527

531 531 531 531 531

Fungi and other Microorganisms (Actinomycetes, Bacteria, Oomycota, Phytoplasmas) Index

532

Plant Index

548

Eucalypt (Angophora, Corymbia, Eucalyptus) Scientific Names Eucalypt (Angophora, Corymbia, Eucalyptus) Common Names Other Plants

Subject Index

548 552 556

558

xi

This Page Intentionally Left Blank

P R E F A C E

The eucalypts (genera Eucalyptus, Corymbia and Angophora) are a unique group of mainly tree species. Despite more than two centuries of scientific study, their taxonomic circumscription is still incomplete. As recently as July 2000, 11 new and disparate species were described from tropical and subtropical Australia (Hill, K.D. and Johnson, L.A.S., 2000, Telopea 8, 503–539). From early European perceptions of them as strange, tough, unwanted trees that dominated the harsh landscape and frustrated the early agricultural development of the isolated continent of Australia, they have become taxa of worldwide importance for large-scale and small-scale planting (see Chapter 1). They now include the most widely planted hardwoods in diverse climates around the world, including the semiarid regions of North Africa, Central Asia and the Middle East, the Mediterranean regions of North Africa, southern Europe, the Middle East and California, the cool mountain regions of South America and Africa, and the tropics and subtropics of Central and South America, Africa and Asia. Eucalypts have become an integral part of the South American landscape, to the extent that they are a pervading presence in the literature of the region. In India, China and Vietnam they have become so well established that people refer to local landraces of particular species or hybrids. In the warmer climatic regions, they are important ecologically, socially and industrially. As well as helping to meet the growing world demand for cellulose fibre, timber and fuelwood, they are being used to renew the seriously depleted timber and firewood resources associated with poverty in many countries, for soil stabilisation in degraded environments and as an addition to the garden resources of subsistence farmers (see Chapter 1). This book is concerned with disease in trees

growing in a wide range of situations, from native plant communities being managed for conservation purposes or mainly for timber and fibre production to intensively managed plantations. Many species of eucalypts are in the process of domestication. Increasingly, even in Australia, the trend is towards the planting of eucalypts and their manipulation by selection, breeding, clonal propagation and intensive silviculture. Seed of a great diversity of provenances collected from the wild in Australia, Papua New Guinea and Indonesia is being used in selection and breeding programs in many countries. In Australia, there has been increasing awareness of the importance of the eucalypts in their natural environment, particularly for land conservation and protection, for conservation of native flora and fauna, and for the conservation of the ultimate repository of the vast genetic resource of eucalypt species, provenances and families adapted to a diverse range of environments. This has led to the development of forest and land management practices concerned with their protection and preservation, and the restoration of degraded eucalypt-dominated communities. The more than 700 species of eucalypts range from those adapted to the semiarid environments that dominate much of the Australian continent, to those, including some of the world's tallest and most majestic trees, adapted to the cooler, wetter environments in the south-east and south-west of the country, to those adapted to the warm, wet environments in the northern subtropical and tropical regions (see Chapter 4). Ring counts on free-standing, single-stemmed trees in the tall forests have provided evidence of their great longevity (up to 450 years) (Hickey, J.E., Su, W., Rowe, P., Brown, M.J. and Edwards, L., 1999,

xiii

D I S E A S E S

A N D

P A T H O G E N S

O F

Australian Forestry 62, 66–71). Although the eucalypts still dominate the Australian landscape, since European settlement there have been massive changes in the scale and condition of eucalypt forests and woodlands resulting from large-scale clearing for agriculture and urban development, introduction of exotic plants and animals, alteration to fire regimes, harvesting, and changes in hydrological balance and salinity across the landscape. Further changes to the situation of eucalypts in Australia have accompanied the planting of eucalypts in altered rural and urban environments, as individual trees, shelter belts, amenity plantings or in large plantations. These changes, relatively sudden in evolutionary terms, have led to an increased awareness of the physiological and nutritional requirements of the eucalypts (see Chapters 5 and 16), of the importance of eucalypt mycorrhizas (see Chapter 6), and of the potential destructiveness of pests and diseases. Since the 1950s, it has become increasingly apparent that many remnant native forests and woodlands are suffering ill health, with symptoms generally referred to as ‘dieback’, associated with environmental stresses and increased pest and disease pressure. Remnant trees in agricultural and grazing lands have suffered increasingly from ‘rural dieback’, a syndrome associated with increased insect attack (see Chapter 17). Large areas of forest in south-east and south-west Australia have suffered decline and, in certain forests, mass deaths caused by Phytophthora cinnamomi (see Chapter 11). Patches of forest in south-east Australia were killed by the native agaric, Armillaria luteobubalina (see Chapter 12). The early attempts at cultivation of eucalypts in plantations in Australia revealed the potential destructiveness of several highly adapted leaf pathogens (see Chapter 9). These diseases alerted the community to the dangers of increased occurrence and intensity of disease epidemics associated with the great changes wrought by European settlers on native eucalypt vegetation. When eucalypts were first grown outside Australia in the absence of their coevolved parasites, they often appeared healthier and more vigorous than in their native lands. Later, as the plantings became more extensive, the trees began to suffer attack by nonspecialist pathogens, especially in the humid subtropics and tropics. In New Zealand, they were badly damaged by leaf pathogens introduced from Australia, while in South Africa they were attacked

xiv

E U C A L Y P T S

by some pathogens which appear to have spread from local plants onto the introduced eucalypts. In South America, a destructive rust pathogen and a canker pathogen have transferred to eucalypts from local myrtaceous hosts. There are serious concerns that if these ‘new-encounter’ pathogens are introduced to Australia they could cause great damage in eucalypt-dominated vegetation. Certainly the widespread planting, often in intensive culture, of eucalypts around the world has created new opportunities for the adaptation and spread of pathogens and pests. As a result of the occurrence of disease problems in both native eucalypt communities and plantations outside Australia, there has been an upsurge in interest in the pathology of eucalypts over the last 40 years, as reflected in the burgeoning literature on the subject. It is an opportune time to review knowledge of the biotic and abiotic factors affecting the health of eucalypts, and to bring together the disparate literature on the subject as a basis for further research. With this in mind, Geoff Marks initiated the writing of this book. His death in 1990 prevented his participation beyond the planning stage, but the eventual production of the book is a tribute to his enthusiasm for the field of eucalypt health, his 27 years of research on diseases of eucalypts, particularly dieback associated with Phytophthora cinnamomi, and the encouragement he gave to others. This book is intended not only as a catalogue of current knowledge about the diseases of eucalypts but also as a handbook to facilitate further research into their biology and management. The book is concerned with the health of eucalypt-dominated plant communities in Australia, and of small social plantings and large industrial plantations around the world, not just with a narrow account of diseases of the trees. The rapid expansion of eucalypt planting, first outside and lately within Australia, and the more intensive management of native forests have resulted in a growing interest in the physiology, nutrition, adaptation, genetics, ecology, silviculture and management of the eucalypts. While the book has a strong emphasis on disease in production forests, it also addresses disease in native eucalyptdominated forests and woodlands and in remnant or isolated, planted eucalypts.

P R E F A C E

The book concerns a complex and wide ranging field. Accordingly, it includes a substantial introduction to the biology, ecology and physiology of the eucalypts (Section I) as a basis for further discussion of particular diseases (Section II) and the management options for these diseases in natural, semi-natural and planted communities (Section III). In particular, the genetic diversity of the eucalypts and their adaptation to a wide climatic and edaphic range in Australia and nearby countries is discussed in some detail in Chapter 2 and Chapter 4 as a basis for development of disease management through matching of genotypes to sites and selection of disease resistant planting stock. This book should serve as a timely reminder that the eucalyptdominated communities across Australia and in nearby countries are an invaluable repository of the diverse genetic resource of the eucalypts. In Chapter 3, the growth habits and silviculture of eucalypts is discussed in relation to development of management strategies for maintaining forest health. The ecology of eucalypt regeneration in native communities is introduced in Chapter 4 as a basis for developing knowledge and management expertise in control of diseases in the most disease-prone phases of forest management, namely regeneration in native forests, and production of planting stock and early establishment in plantations. Harvesting and regeneration activities in native forests often result in dense seedling regeneration which may suffer severe epidemics of foliar disease not unlike those expected in crowded plantations. The physiology of eucalypts in relation to their response to stresses including pathogens is introduced in Chapter 5 in anticipation of future research on the physiological effect of diseases of eucalypts and how this might be ameliorated. Chapter 6 reviews knowledge of the mycorrhizas of eucalypts, a subject of great importance to the nutrition and health of the trees. Mycorrhizas are of concern to all involved in management of eucalypt forests and are of particular interest to anyone with a mycological interest in the forests, particularly plant pathologists who are often involved in research into mycorrhizas as well as diseases. This chapter provides a basis for further research on manipulation of mycorrhizas for adaptation of eucalypts to new sites and for combating soilborne diseases. Knowledge of the biology of eucalypts is crucial for developing disease management practices, especially for diseases of native forests and woodlands, which often have

complex etiology and can be ameliorated only by modification of normal silvicultural practices. The chapters in Section II include much background biology of the diseases and their causal organisms, along with discussion of the pathology and management of the diseases. This allows the chapters to stand alone as an introduction to the diseases. In Chapter 9, on foliar diseases, it was necessary to include much taxonomic detail of the causal organisms, reflecting the early stage of development of research into these diseases. Throughout the book, the presentation of Latin binomials of fungal species and their authorities follows Authors of Fungal Names by P.M. Kirk and A.E. Ansell, published by the International Mycological Institute, Kew, in 1992. However, the style of R.K. Brummitt and C.E. Powell (1992, Authors of Plant Names, Royal Botanic Gardens, Kew) has been followed in omitting gaps between initials and surnames. The inclusion of taxonomic details of the fungi referred to in the literature has helped to highlight and clarify discrepancies in the naming of fungi. Much synonymy exists and the organism index, researched and compiled by B.N. Brown, serves as an invaluable guide to the current state of nomenclature. Authorities and Australian common names for eucalypt species are listed in the Index. In Chapter 15, on phanerogamic parasites, much underlying ecology of the parasites is presented as a basis for their management in remnant eucalypt vegetation and on forest verges in Australia. Management of nutritional disorders requires knowledge of the physiological role and interactions of various nutrients (see Chapter 16). In Section III, the options and constraints for management of disease in both native forests and plantations are discussed (see Chapter 18). In Chapter 19, detailed approaches to management of disease in native forests are discussed, with particular emphasis on management of dieback caused by Phytophthora cinnamomi, which has been central to forest pathology in Australia for four decades. A particular instance of intensive management of eucalypt dieback in association with bauxite mining in the Eucalyptus marginata forests of southwest Australia is reviewed in Chapter 20. Finally, the more intensive disease management practices in eucalypt nurseries (see Chapter 21) and plantations (see Chapter 22) are reviewed from an international perspective.

xv

D I S E A S E S

A N D

P A T H O G E N S

O F

Although the book provides a comprehensive review of the state of knowledge of eucalypt diseases, it also shows that our knowledge of most diseases is preliminary—there is much to be learnt. We hope that this book will provide a basis for more intensive

xvi

E U C A L Y P T S

studies of the nutrition, adaptation and diseases of the eucalypts, leading to improved health, productivity and sustainability of these species in native eucalypt communities, and in both large plantations and smaller plantings around the world.

C O N T R I B U T O R S

D.H. Ashton Department of Botany, La Trobe University, Bundoora, Vic. 3083, Australia Email: [email protected]

David Ashton completed his PhD in 1956 at the University of Melbourne on the ecology of Eucalyptus regnans and then undertook further studies at Cambridge University, in Germany and in the USA. In 1960, he took up a lectureship in ecology in the School of Botany at the University of Melbourne, where he continued research on the ecology of E. regnans and diversified into studies of a wide range of ecosystems from coastal heath to alpine-antarctic. From 1975 to 1986 he collaborated on ecological studies of the forests of Chile and Argentina. He is an Associate of the School of Botany and also a Research Fellow in the Department of Botany, La Trobe University. C.L. Beadle Cooperative Research Centre for Sustainable Production Forestry and CSIRO Forestry and Forest Products, GPO Box 252-12, Hobart, Tas. 7001, Australia Email: [email protected]

Chris Beadle obtained his PhD in Botany from the University of Aberdeen in 1977. Since 1983 he has worked for CSIRO Forestry and Forest Products in Hobart, where he is now a Principal Research Scientist and Program Manager of the Sustainable Management Program in the Cooperative Research Centre for Sustainable Production Forestry. B.N. Brown 15 Harefield Street, Indooroopilly, Qld 4068, Australia Email: [email protected]

Bruce Brown obtained his BAgSc (Hons) from the University of Queensland in 1963 and his PhD from the University of Auckland in 1978. He was a Forest Pathologist with the Queensland Department of Forestry (subsequently the Forest Service of the

Queensland Department of Primary Industries) from 1963 until 1991. He studied a wide range of forest diseases in nurseries, plantations and natural forests. He was heavily involved in the control of nursery diseases, and investigated Phytophthora cinnamomi in forest nurseries, Pinus and Eucalyptus plantings and natural vegetation (including tropical rainforests) of Queensland. Recently he has worked as consultant on several projects. G.A. Chilvers 23 Keats Street, Byron Bay, NSW 2481, Australia Email: [email protected]

Graham Chilvers obtained his BScAgr from the University of Sydney, majoring in Plant Pathology under Professor N.H. White, and his PhD at the Australian National University, working on mycorrhizas of eucalypts under Professor L.D. Pryor. He spent two periods of sabbatical leave at the University of Oxford working on mycorrhizas with Professor J.L. Harley. For most of his career he was a Senior Lecturer in the Botany Department, Australian National University. His major research interest was in eucalypt mycorrhizas, but he also studied and lectured in diverse areas of plant-microbe relationships and microbial ecology. I.J. Colquhoun Alcoa of Australia, Booragoon, WA 6154, Australia Email: [email protected]

Ian Colquhoun is a Senior Research Scientist with the Environmental Department of Alcoa World Alumina Australia. He received his BSc in Botany from the University of Glasgow in 1976, and his PhD from the University of Western Australia in 1986 for a dissertation on the physiology of Australian native plants. In 1980, he joined Alcoa to supervise a project on the hydrological balance of revegetated minepits. In 1989, his responsibilities extended to the interaction between the hydrology of rehabilitated minepits, tree xvii

D I S E A S E S

A N D

P A T H O G E N S

O F

E U C A L Y P T S

physiology and Phytophthora root rot. His present responsibilities include the development of disease control measures for mining, coordinating plant pathology research projects and supervising plant physiology projects based in the jarrah forest and rehabilitated minepits.

Davis. Since 1971 he has lectured at the University of Brasilia where he is currently Professor and Chairman of the Department of Plant Pathology. He has conducted research on a wide range of diseases of agricultural and forest species, with an emphasis on diseases of eucalypts, especially guava rust and bacterial wilt.

P.W. Crous Department of Plant Pathology, University of Stellenbosch, Private Bag XI, Matieland 7602, South Africa Email: [email protected]

Pedro Crous did his MSc(Agric) on leaf diseases of Eucalyptus, which set the stage for much of his future research. He obtained his PhD(Agric) in 1992, dealing with Cylindrocladium and related fungi, with specific reference to woody hosts. He has since continued studies on this group, but also initiated projects on Mycosphaerella, Botryosphaeria and their anamorphs. His main interests are anamorph/ teleomorph connections, and the integration of DNA and morphological data in the phylogeny of fungi. He is Professor of Mycology and Chair of the Department of Plant Pathology at the University of Stellenbosch. He is also the President of the Southern African Society for Plant Pathology.

M.A. Dick New Zealand Forest Research Institute, Private Bag 3020, Rotorua, New Zealand Email: [email protected]

Margaret Dick obtained a BSc in Botany and has worked since 1972 as a forest pathologist with the New Zealand Forest Research Institute, concentrating on fungal diseases. She has studied foliage diseases of eucalypts in plantations, root diseases of pine, and more recently Cyclaneusma needle cast of Pinus radiata. She has also been involved in pest risk analysis, particularly of the threat posed by pine pitch canker to plantation forests in New Zealand. For over 20 years she has supervised the forest disease diagnostic service. This has included identification and monitoring of foliage diseases on eucalypt species during their testing for adaptation to local conditions. P.E. Elliott

E.M. Davison School of Environmental Biology, Curtin University, GPO Box U 1987, Perth, WA 6001, Australia Email: [email protected]

Elaine Davison received her BSc Honours from the University of Bristol in 1963 and her PhD from the same university in 1967. From 1968 to 1972 she worked as a Plant Pathologist at the Botanic Garden and at the Waite Agricultural Research Institute in Adelaide. In 1979, she was a post-doctoral research fellow at the University of Oxford. From 1979 to 1986 she worked as a Mycologist/Plant Pathologist with the Department of Conservation and Environment, and from 1986 to 1995 she was a Principal Research Scientist at the Department of Conservation and Land Management in Western Australia, concerned with diseases of eucalypts. She is now a Senior Research Associate and works as a consultant based at Curtin University of Technology.

WMC Resources Ltd, QV1 Building, 250 St George’s Terrace, Perth, WA 6000, Australia Email: [email protected]

Peter Elliott obtained his MSc in Natural Resource Management from the University of Western Australia. In 1990 he was the senior environmental scientist with Alcoa and coordinated the development of the intensive dieback management program. This involved him in developing strategies, policies and procedures for management of operations in jarrah forests, in consultation with a wide range of Alcoa employees and government agencies. As Corporate Manager—Environmental Systems, he was later responsible for the development of Environmental Management Systems for WMC Resources Ltd. He has recently been appointed Manager—Planning and System Services in the Corporate Human Resources and Development Group of the company. F.A. Ferreira

J.C. Dianese Departmento de Fitopatologia, Universidade de Brasilia, 70919 Brasilia, DF, Brazil Email: [email protected]

Jose Dianese obtained his BS in agronomy from the Universidade Federal de Viçosa and his MS and PhD in plant pathology from the University of California, xviii

Departmento de Fitopatologia, Universidade Federal de Viçosa, 36571.000 Viçosa, Minas Gerais, Brazil Email: [email protected]

Francisco Ferreira is a forest pathologist with over 25 years of experience in teaching, research and extension on the etiology and management of forest diseases in Brazil, including diseases on eucalypts, pines and

C O N T R I B U T O R S

rubber. He has been concerned with nursery diseases, rust diseases and defence mechanisms in the bark and xylem as they relate to the diagnosis and control of biotic and abiotic trunk diseases. He has undertaken extension activities related to the diagnosis and management of diseases of eucalypts for both private companies and public institutions in Brazil and other countries in South America and Europe. He is currently Professor of Forest Pathology at the Federal University of Viçosa. R.G. Florence Department of Forestry, Australian National University, GPO Box 4, Canberra, ACT 2601, Australia Email: [email protected]

Ross Florence graduated from the Australian Forestry School and the University of Queensland in 1953 and worked on silviculture of native forests with the Queensland Forest Service. He obtained his PhD from the University of Sydney in 1961 for studies on the ecology of native forests. He joined the Department of Forestry of the Australian National University in 1965 where he lectured in silviculture, forest ecology, and planning and policy. He wrote Ecology and Silviculture of Eucalypt Forests, published by CSIRO Publishing in 1996. P.D. Gadgil New Zealand Forest Research Institute, Private Bag 3020, Rotorua, New Zealand Email: [email protected]

Peter Gadgil obtained his PhD in the area of microbial ecology from the University of Cambridge in 1962 and has been a forest pathologist with the New Zealand Forest Research Institute since 1965. His main areas of work have been needle diseases of Pinus radiata (Dothistroma needle blight, Cyclaneusma needle cast), stem decay in Eucalyptus spp. and, with Ruth Gadgil, the influence of mycorrhizal fungi on litter decomposition in coniferous forests. More recently, he has concentrated on the eradication of Dutch elm disease from New Zealand, methods of forest health surveillance and the investigation of pathways by which forest pests and pathogens can reach New Zealand.

a research scientists with CSIRO Forestry and Forest Products in Clayton, Vic., where he worked for 21 years until 2000, specialising in decay of wood and natural durability of timber. P.J. Keane Department of Botany, La Trobe University, Bundoora, Vic. 3083, Australia Email: [email protected]

Philip Keane obtained a BAgSc(Hons), specialising in plant pathology, from the University of Adelaide, and a PhD from the University of Papua New Guinea for studies on the cause and control of a dieback disease of cocoa. Since 1975 he has lectured in botany, environmental biology, mycology and plant pathology at La Trobe University where he is now an Associate Professor. His research interests include foliar diseases of eucalypts and diseases of a wide range of agricultural crops, with a special interest in resistance to disease, biological control and plant diseases in the tropics. G.A. Kile CSIRO Forestry and Forest Products, PO Box E4008, Kingston, Canberra, ACT 2604, Australia Email: [email protected]

After completing his BAgrSc(Hons) and PhD at the University of Tasmania, Glen Kile undertook research on diseases in native forests in Australia, particularly Armillaria and stem rot fungi in eucalypts, Chalara australis in Nothofagus forests, and some dieback diseases of complex etiology. He identified Armillaria luteobubalina as a major pathogen in eucalypt forests, amenity plantings and horticulture in Australia and conducted taxonomic and population studies of Armillaria. He was appointed Director of the Cooperative Research Centre for Temperate Hardwood Forestry in 1991, Chief of CSIRO Division of Forestry in 1992 and Chief of CSIRO Forestry and Forest Products in 1996. He is a member of the Standing Committee on Forestry of the Australian Ministerial Council on Forestry, Fisheries and Aquaculture, and Chairman of its Committee on Forest Health. He is a member of the editorial boards of Australasian Plant Pathology and the European Journal of Forest Pathology.

G.C. Johnson 10 Glendowan Road, Mt Waverley, Vic. 3149, Australia

Gary Johnston completed his BScFor(Hons) and MSc(Forestry) at the University of British Colombia and obtained his PhD from the Australian National University where he studied under Professor D.M. Griffin and Dr W.A. Heather. He taught forestry at the University of Melbourne before taking up a position as

K.M. Old CSIRO Forestry and Forest Products, PO Box E4008, Kingston, Canberra, ACT 2604, Australia Email: [email protected]

Ken Old obtained his BSc(Hons) in agricultural botany from the University of Nottingham in 1961 and his PhD from the University of Minnesota in 1964. He lectured xix

D I S E A S E S

A N D

P A T H O G E N S

O F

E U C A L Y P T S

in plant pathology, mycology and soil microbiology at Dundee University from 1964 to 1978. He joined CSIRO Forestry and Forest Products in 1978 and was Assistant Chief from 1992 to 1999. He is currently a Chief Reseach Scientist. His main research interests have included genetic variation in Phytophthora cinnamomi, canker diseases of eucalypts, foliar pathogens of eucalypts and acacias in plantations in tropical Australia and south-east Asia, and stem defect in regrowth eucalypt forests in south-east Australia. R.F. Park University of Sydney, Plant Breeding Institute Cobbitty, PMB 11, Camden, NSW 2570, Australia Email: [email protected]

Robert Park obtained his BSc(Hons) and PhD from La Trobe University where he studied the pathology of Mycosphaerella species infecting eucalypts in southeast Australia. He is currently a Senior Research Fellow at the University of Sydney, Plant Breeding Institute, Cobbitty, where he works as a plant pathologist concerned mainly with ecological aspects of cereal rusts and breeding of cereals for resistance to rusts. He was awarded an Alexander von Humbolt Fellowship in 1995 and spent one year at the Technical University of Munich studying European populations of wheat leaf rust. Since his student days he has maintained an interest in the diversity of the foliar pathogens of eucalypts. L.A. Pederick 17 Yanigin Drive, Glen Waverley, Vic. 3150, Australia

Leon Pederick obtained his BScFor and PhD from the University of Melbourne and worked as a research scientist for the forest service of the Victorian Government from 1958 to 1993. He specialised in genetics of forest trees and for over 30 years led a breeding program for Pinus radiata. He also undertook extensive provenance and progeny trials with several eucalypt species, especially Eucalyptus nitens. He is a Fellow of the Institute of Foresters of Australia, and was awarded the Institute's N.W. Jolly Medal for 1991. F.D. Podger 19 Stanstead Crescent, Marangaroo, WA 6064, Australia

Frank Podger obtained a BSc(For) from the University of Western Australia, a DipFor from the Australian Forestry School, Canberra, an MScFor from the University of Melbourne, and a PhD from the University of Auckland. His early career with the WA Forests Department involved field training in forest management in eucalypt forests. In 1959, under federal employ he researched the cause of a destructive xx

epidemic of dieback in the jarrah forests, first reporting in 1964 its association with the exotic pathogen Phytophthora cinnamomi and publishing proof of its cause in 1972. For this he received an inaugural Scientific Achievement Award from IUFRO. He has since studied diseases of native vegetation in all States of Australia and has also had an interest in fire effects ecology and its interactions with Ph. cinnamomi. In the last decade he has consulted to governments in Tasmania and Western Australia on management for amelioration of disease in native forests and its sociopolitical implications. From 1993 to 1996 he chaired a review of management of Phytophthora root rot in Western Australia. In 1999, he produced a source document on which was based a National Threat Abatement Plan for amelioration of the threat posed to conservation values by the epidemic of Phytophthora root rot. B.M. Potts Cooperative Research Centre for Sustainable Production Forestry, School of Plant Science, University of Tasmania, GPO Box 252-55, Hobart, Tas. 7001, Australia Email: [email protected]

Brad Potts completed his PhD at the University of Tasmania in 1983 where he is currently a Senior Lecturer in the School of Plant Science and Manager of the Genetic Improvement Program of the Collaborative Research Centre for Sustainable Production Forestry. Within this program he is leader of the research project on the reproductive biology and genetics of eucalypts and works closely with quantitative and molecular geneticists at the University of Tasmania on the natural history and breeding of eucalypts. He has worked in and maintains active research collaboration with scientists in France, Chile and the USA and has specialised in studies of hybridisation, genetics and evolution of the eucalypts. N. Reid Ecosystem Management, University of New England, Armidale, NSW 2351, Australia Email: [email protected]

Nick Reid completed a BSc(Hons) and PhD in Botany at the University of Adelaide. His early research career spanned ornithology, rangeland ecology and the reproductive and population biology of arid zone mistletoes. An academic posting in Mexico led to ecological research on the vegetation dynamics, phenology and ethnobotany of subtropical thornscrub. He is currently Associate Professor and Convenor of Ecosystem Management in the School of Rural Sciences and Natural Resources at the University of New

C O N T R I B U T O R S

England, where he teaches agroforestry, park and wildland management, and sustainable land management. His current research includes the role of trees in farm ecosystems, native vegetation management in rural and wildland environments, revegetation technologies and mistletoe management. J.K. Sharma Kerala Forest Research Institute, Peechi Trichur 680 653, Kerala, India Email: [email protected]

Jyoti Sharma obtained his PhD in Botany (Plant Pathology) from Agra University and was a lecturer at Agra College for eight years. Later, he spent five years at the Australian National University, Canberra, doing post-doctoral research in forest pathology. He joined the KFRI in 1978 as the Scientist-in-Charge, Plant Pathology Division. He was appointed Research Coordinator of the Institute in 1996 and Director in July 2000. He is presently the IUFRO Working Party Coordinator on Diseases of Tropical Plantations. He has had extensive research and consulting experience on diseases and mycorrhizas in eucalypt plantations. He served as an Expert Member on an FAO/IPGRI committee to frame guidelines for the safe movement of eucalypt and pine germplasm and is a Fellow of the Indian Phytopathological Society. B.L. Shearer Department of Conservation and Land Management, 50 Hayman Road, Como, WA 6152, Australia Email: [email protected]

Bryan Shearer obtained a BScAgric(Hons) from the University of Western Australia and a PhD from the University of Minnesota, USA. He is a Principal Research Scientist in the CALM Science Division of the Department of Conservation and Land Management of Western Australia and Adjunct Associate Professor in the Division of Science at Murdoch University. He has investigated the impact, epidemiology and control of Phytophthora species, Armillaria luteobubalina and canker fungi in native plant communities for over 20 years. His current research interests centre on the ecology and control of plant diseases in conservation areas of south-west Western Australia. J.A. Simpson Forest Research and Development Division, State Forests of NSW, PO Box 100, Beecroft, NSW 2119, Australia Email: [email protected]

Jack Simpson is Senior Forest Pathologist with the Research and Development Division of State Forests of

New South Wales, where he has worked for almost 20 years. He obtained an MAgSc from the University of Adelaide for a thesis on mycological aspects of the decomposition of litter of Pinus radiata. During his career Jack has worked on diverse forest disease problems in South Australia, New South Wales, Western Australia, Papua New Guinea and Fiji. He is Chair of Research Working Group 7 (Forest Health), a member of the Forest Health Committee, and the forestry observer on the Plant Health Committee of the Standing Committee on Forestry. He is past president of the Australasian Mycological Society. His research interests include eucalypt foliage pathogens, stem decays in living trees, quarantine issues relating to management of incursions of quarantine pests and imports of wood, and forest declines. I.W. Smith Centre for Forest Tree Technology, Department of Natural Resources and Environment, PO Box 137, Heidelberg, Vic. 3084, Australia Email: [email protected]

Ian Smith obtained a BSc(Hons) from Monash University and is a forest pathologist in the Centre for Forest Tree Technology of the Department of Natural Resources and Environment. He is responsible for investigating the productivity and ecology of native forests, and the biology and control of diseases that threaten the productive capacity of native forests, softwood and hardwood plantations and nurseries. He has over 20 years of experience in the field of forest pathology research in Victoria, much of which was centred on eucalypt dieback caused by Phytophthora cinnamomi. P. Snowdon CSIRO Forestry and Forest Products, PO Box E4008, Kingston, Canberra, ACT 2604, Australia Email: [email protected]

Peter Snowdon is a Principal Research Scientist with the Plantation and Farm Forestry Program of CSIRO Forestry and Forest Products. He majored in plant pathology at the University of Sydney and gained his MSc from the Australian National University for a study of boron nutrition in pines. He has 40 years of experience in various aspects of forest nutrition, including the use of visible symptoms and chemical analyses of soil and foliage samples for identification of nutrient deficiencies and toxicities. He has also been involved in research into the effects of environmental factors such as drought and frost on the growth and health of plantation species. xxi

D I S E A S E S

A N D

P A T H O G E N S

O F

E U C A L Y P T S

J.W. Turnbull

M.J. Wingfield

CSIRO Forestry and Forest Products, PO Box E4008, Kingston, Canberra, ACT 2604, Australia Email: [email protected]

Forestry and Agricultural Biotechnology Institute, University of Pretoria, 74 Lunnon Road, Hillcrest, Pretoria, Republic of South Africa 0002 Email: [email protected]

John Turnbull has a BSc degree in forestry from the University of Wales and a PhD in eucalypt genecology from the Australian National University. As a Senior Principal Research Scientist at CSIRO Forestry and Forest Products he was involved for over 25 years in the exploration and utilisation of eucalypt genetic resources in Australia and many other countries. Subsequently he was Chief Scientist at the Center for International Forestry Research in Indonesia. He is currently based at the Australian Tree Seed Centre, CSIRO Forestry and Forest Products, Canberra.

Mike Wingfield has a PhD from the University of Minnesota and is the Director of the Forestry and Agricultural Biotechnology Institute, University of Pretoria, South Africa. He has 20 years of experience in research on diseases of forest trees and has specialised in the identification and management of diseases of eucalypts, pines and wattles grown as exotics in plantations. He has provided advisory services to forestry companies in South Africa, South and Central America, and south-east Asia.

T.J. Wardlaw Forestry Tasmania, GPO Box 207B, Hobart, Tas. 7001, Australia Email: [email protected]

Tim Wardlaw obtained a BScHons and is completing a PhD at the University of Tasmania. He is Senior Forest Pathologist with Forestry Tasmania. In a career spanning 20 years he has investigated a wide variety of forest diseases including eucalypt crown dieback diseases with complex etiologies, needle cast diseases of Pinus radiata and stem decay of eucalypts in native forests and plantations. Recently much of his work has been focused on quantifying the effects of diseases and developing management strategies to reduce disease losses. He has overseen the introduction and development of health surveillance of eucalypt and pine plantations in Tasmania.

xxii

Z. Yan Plant Research and Development Services, Agriculture Western Australia, Baron Hay Road, South Perth, WA 6151, Australia

Zhaogui Yan studied agricultural science at the Central China University of Agriculture and completed his PhD in mistletoe ecology at Flinders University, South Australia. He currently works for Agriculture Western Australia where his principal research interests are managing annual ryegrass toxicity through biological control, the population dynamics of rangeland plants under various climatic and grazing regimes, and the ecological interactions between mistletoes and their hosts and dispersers.

C H A P T E R

E CONOMIC E UCALYPTS

AND

S OCIAL I MPORTANCE

OF

1

J.W. Turnbull

S

U M M A R Y

For thousands of years eucalypts have been of critical importance in the economy of indigenous Australians. In the last 200 years eucalypts have passed from being a botanical curiosity and nuisance to the early European settlers in Australia, to trees of importance in the local economy, to one of the world’s most important and widely planted forest species. Eucalypts have valuable wood and pulp characteristics and many useful silvicultural properties including high growth rates, adaptability to a wide range of soils and climates, coppicing ability and a tendency not to spread as a weed. In Australia, eucalypt-dominated native forest and woodland communities cover about 124 million hectares but wood and pulp production is restricted to about 13 million hectares. It is estimated that there will be 20 million hectares of eucalypt plantations outside Australia by the year 2010. At present there are more than 10 million hectares in the tropics alone, mainly in South America and Asia. Since the early 1980s, eucalypt planting has expanded rapidly in many parts of the world, including Australia. This expansion has been driven by the world demand for pulpwood, but eucalypts are also being planted widely as a source of charcoal, fuelwood and building materials and for land conservation. The trees can provide a source of financial security for small farmers. Great benefits have accrued from clonal selection and breeding of eucalypts and from more intensive management practices, in which Brazil has led the way. However, it is important to recognise the increased risk of disease epidemics associated with the movement of pathogens to new areas and the establishment of densely planted, genetically homogeneous plantations. Outbreaks of disease in plantations and native forests have stimulated much recent research into the diseases of eucalypts.

1

D I S E A S E S

A N D

P A T H O G E N S

O F

1.1 Introduction The eucalypts (genera Eucalyptus, Corymbia, Angophora), being by far the dominant tree over most of the Australian landscape, have been critical to the economy of indigenous Australians, directly supplying fuel, building materials, medicine and resins, and being habitat for the animals that contributed greatly to their diet. In the late eighteenth century when eucalypts first came to the attention of the scientific world and the French botanist, Charles Louis L’Héritier De Brutelle, applied the name Eucalyptus to an Australian tree, there was little appreciation of the potential of eucalypts to become a major source of industrial forest products. The wood was difficult to saw and season and it was commonly considered to have value only as firewood or as poles. Remarkably, at the beginning of the twenty-first century the natural eucalypt forests are a major source of forest products, and eucalypts have become the most widely planted hardwood species in the world.

1.2 Eucalypts in native forests Eucalypts dominate 124 million hectares of Australia’s natural forests and woodlands (Australian Bureau of Agricultural and Resource Economics 1997) (see Chapter 4) and they have great cultural and environmental significance, as well as being a valuable source of wood products. Most of this area is eucalypt woodland. Only about 28 million hectares is potentially productive forest (Australian Forestry Council 1989). Production of wood for industrial purposes is restricted to about 13 million hectares by factors such as lack of accessibility and conservation reserves (Commonwealth of Australia 1997). Beyond Australia there are small areas of natural eucalypt forests in Indonesia, Papua New Guinea and the Philippines but these are of relatively little economic significance, even locally. When European settlement began in Australia in 1788, trees were considered to be a hindrance to development. Clearing of land for agriculture was essential and large areas of eucalypts were felled. About half of Australia’s forests have been cleared or severely modified by selective logging or uncontrolled fires (Wells et al. 1984; Resource Assessment Commission 1992). Attitudes to the forests changed markedly around the start of the

2

E U C A L Y P T S

twentieth century and State forest services were established to manage public forests for perpetual timber production. By the 1930s the concept of ‘multiple use forestry’ was recognised and forests were dedicated for watershed protection, recreational use and the conservation of native wildlife and flora, in addition to timber production (Carron 1985). The supply of eucalypt timber has generally exceeded demand in Australia and there has been little incentive to manage eucalypts intensively for wood production (Kerruish and Rawlins 1991). In most States the harvest of eucalypt sawlogs increased progressively from about 1930 but is now declining from peaks reached between 1955 and 1980. Today, eucalypt forests meet about half of Australia’s domestic requirements for forest products, the remainder being imported or derived from local plantations of softwood (mainly Pinus species). However, pulpwood production from eucalypt forests increased dramatically from the early 1970s, particularly in Tasmania, Western Australia and New South Wales, with the development of an export market for Australian eucalypt woodchips to meet increased demands for printing, writing and tissue papers. The volume harvested has remained fairly stable through the 1990s. In 1997–98 some 10.3 million cubic metres of native hardwoods (mainly eucalypts) were removed for timber and woodchips and it is predicted that this level will be maintained until 2005 (Australian Bureau of Agricultural and Resource Economics 1999). In 1997, exports of hardwood chips reached 2.5 million tonnes (bone dry). Woodchip, including softwood chips, has generally accounted for just over half of the value of Australian forest product exports in the 1990s and reached a record $646 million in 1997–98 (Australian Bureau of Agricultural and Resource Economics 1999). However, the wood and wood products industry contributes only about 1% of Australia’s gross domestic product. While the eucalypt wood industry is small within the overall Australian economy, the various sectors of the industry together employ about 40 000 people and have great significance in providing employment and economic activity in particular regions (Resource Assessment Commission 1991). Eucalypt growing, harvesting and processing are the major activities of several small rural communities.

E CON OMI C

A ND

There seems little doubt that the natural eucalypt forests will continue to have considerable economic significance in Australia. By the year 2005 the annual hardwood removals (mainly eucalypt) from Australia’s native forests will be 10.1 million cubic metres (Australian Bureau of Agricultural and Resource Economics 1999). There are also excellent opportunities for the more intensive management of some of the higher-yielding temperate forests in Australia, and a young regrowth eucalypt resource of about 300,000 ha is possibly amenable to intensive management (Wells 1991). The area under eucalypt plantations is being expanded to meet pulpwood needs and possibly some sawlog requirements. As a result of an active eucalypt plantation program with E. globulus and E. nitens, the area of hardwood plantations in Australia rose from 125,000 hectares in 1994 to 287,000 hectares in 1998 (Cromer et al. 1995; Wood et al. 1999). In addition to the economic value of the native eucalypt forests, they have great societal, cultural and environmental significance. Eucalypt forests and woodlands dominate the Australian landscape. They hold particular significance for Aboriginal peoples (Resource Assessment Commission 1991). They are critical for the protection of soil, maintenance of hydrological balance and the survival of wildlife. Excessive clearing of eucalypts and their associated communities has led to decline of remnant trees and salinity problems in many areas. The native forests and woodlands are also the ultimate repository of the great genetic diversity of the eucalypts. In response to community attitudes and changes in government policies, efforts are increasing to modify forest practices to better address conservation values and the maintenance of biological diversity (Turnbull 1996). Although many of the environmental effects of more intensive culture of eucalypts are incompletely understood, there is no doubt that environmental effects will result from the intensification of forestry practices. However, in most cases the costs imposed on the environment by sustainable harvesting and extension of eucalypt planting will be less than those associated with agriculture or other types of intensive land management on similar land. Benefits of intensive culture of eucalypt plantations will accrue from the reduced land area required for wood and pulp production, the use of a renewable resource and

S OCIA L I MPORTA NCE

OF

E UCA LYPTS

C H A P T E R

1

from the broader socioeconomic effects of such activity (Nambiar and Brown 1997).

1.3 Eucalypts as exotics Outside Australia, eucalypts were initially regarded as botanical curiosities and were sought by botanical gardens and private aboreta in Europe. Once in cultivation, the potential of some eucalypt species to grow rapidly and produce straight stems was recognised and the botanical gardens of southern Europe became centres for the secondary dispersal of eucalypts to other parts of the world, especially Latin America and Africa. Later in the nineteenth century, eucalypts were introduced directly from Australia to many parts of the world. Some were planted for their ornamental value, and others for windbreaks, land reclamation and leaf-oil production. In countries such as Brazil and South Africa, eucalypts were planted along railway lines to provide fuel for woodburning locomotives. The reasons for planting eucalypts have changed significantly, and the end uses to which the various species have been applied are diverse. Eucalypts provide sawn timber, mine props, poles, firewood, pulp, charcoal, essential oils, honey, tannin, shade and shelter (Hillis and Brown 1983). The eucalypt genera Eucalyptus and Corymbia have many favourable characteristics including high growth rates, wide adaptability to soils and climates, ease of management through coppicing, valuable wood properties and absence of any tendency to spread as weeds in most environments. Only a relatively few species from the many in the genera are preferred for fuelwood, pole or pulpwood plantations. The particular species planted depend on the climate. Reliable global estimates for areas of planted eucalypts are difficult to obtain, but published reports (e.g. Davidson 1995) suggest that there were close to 14 million hectares at the end of 1993. Over 90% of these forests have been established since 1955 and about 50% since the mid 1980s (Turnbull 1991). There were over 10 million hectares of tropical eucalypt plantations at the end of 1990, principally in tropical America (4 million ha) and tropical Asia (5 million ha) (Food and Agriculture Organization 1993). The American statistic is dominated by Brazil where there are 3.2 million hectares (EMBRAPA 1996), including part of an area of 2.9 million hectares

3

D I S E A S E S

A N D

P A T H O G E N S

O F

approved for plantation development using government incentives between 1967 and 1984 (Iuseum et al. 1988; Bazett 1993). In tropical Asia, India has over four million hectares including trees planted in various configurations on farms (Davidson 1995). In addition, there are substantial plantations in countries with more temperate climates including Chile 180,000 hectares, China 670,000 hectares, Morocco 200,000 hectares, Portugal 500,000 hectares, South Africa 538,000 hectares and Spain 350,000 hectares (Davidson 1995). Increased areas of eucalypt plantation are projected in several countries. Plantings will continue in Brazil but not at the very high rates of the recent past as there will be more effort to increase the productivity and quality of existing areas. In Portugal too, highly productive clonal plantations of E. globulus are being developed. Both China and India have active reforestation programs, and although there has been some resistance to eucalypt plantations in the latter, the great demand for wood and restrictions on harvesting in native forests will undoubtedly ensure that planting continues. In recent years, eucalypt planting has accelerated in several tropical countries, although extensive planting of eucalypts in the lowland humid tropics has been inhibited by a high incidence of pathogens and insect pests that reduce productivity. Only a few eucalypt species, such as E. deglupta, E. pellita and E. urophylla, are adapted to hot, humid conditions (Werren 1991). Planting of other species tends to result in severe damage by foliar diseases (e.g. Cylindrocladium spp.) associated with trees under stress (see Chapter 9). Despite this, about 200,000 hectares of E. camaldulensis have been established in Thailand (Pousajja 1996) and there are major planting programs in the Congo (Bouillet et al. 1999) and in Vietnam (Tran Xuan Thiep 1996). There are also active plantation programs in the more temperate areas such as those in South America especially in Chile, Paraguay and Uruguay. ‘Opportunities to increase world wood supply in the future will depend on plantations as a consequence of the likely static or decreasing supply from natural forests through deforestation, past overexploitation, greater reservation for nonwood uses or values, and increased costs of access and extraction’ (Kile 1999). If this scenario is 4

E U C A L Y P T S

correct, then the current trend to increase the area of eucalypt plantations will continue and the total area will exceed 20 million hectares by 2010.

1.4 Industrial eucalypt plantations There is no sector of world forestry that is expanding as rapidly as the industrial use of eucalypts. Most plantations are being established to provide mediumdensity to low-density short-fibred pulp for paper. Global short-fibre pulp consumption is about 13 million tons per annum and is growing at 3.9% annually (World Resources Institute 1998). Plantation-grown eucalypt wood is usually harvested after 5 to 10 years and provides a uniform material with high brightness, and good opacity and bulk which make the pulp very suitable for the production of copying, printing, writing and tissue papers. Demand for these products is rising and with it the demand for eucalypt pulp. Brazil is the largest producer of eucalypt pulp: its plantations, mainly of E. grandis, yield annually over two million tons of bleached pulp out of a total world production of about five million tons (World Resources Institute 1998). Portugal was the first country to produce eucalypt sulphite pulp in 1906 (Rolo 1988). Increasing interest over the past 20 years has brought E. globulus to prominence as a major source of income in the Portuguese economy. Portugal is the world’s second largest producer of eucalypt bleached pulp and the pulp industry accounts for the majority of Portuguese forestry exports. Other major eucalypt pulp producers are Chile (E. globulus), Morocco (E. camaldulensis), Spain (E. globulus) and South Africa (E. grandis). Very high levels of investment are required for the pulp and paper industry. In Chile, private investment in forestry was about US$4 billion in 1996 and 15% of these funds were invested in eucalypts. Another example of the high level of investment in the eucalypt pulp industry is the Brazilian company, Aracruz Celulose S.A. Since 1973 the company has invested heavily in research, plantation management and processing plant. Tree improvement with an emphasis on clonal forestry increased the productivity of plantations from 5.9 to 10.9 tonnes per hectare per annum (Bertolucci et al. 1995). The company invested US$1.15 billion in 1990 in an expansion of its pulp mill to lift production to one million tonnes per annum and is planning a 20%

E CON OMI C

A ND

expansion (Aracruz 1991; World Resources Institute 1998). It supplies 22% of the world’s bleached eucalypt pulp and 3% of the world’s total demand for pulp (Campinhos 1999). In 1995, Aracruz Celulose S.A. had a total revenue of US$796 million and is a major contributor to Brazil’s domestic economy. At the same time it contributes health care, housing, education and other benefits to the local communities in and around its plantations (World Resources Institute 1998). However, the greater part of the eucalypt plantations in Brazil is used to provide high quality industrial charcoal for iron and steel production. Minas Gerais State, the centre of Brazil’s iron and steel industry, uses 70% of the wood from its eucalypt forests for production of industrial charcoal. There are several private companies in the State, each managing 150,000 to 200,000 hectares of eucalypt plantations. The main species used in charcoal plantations is E. grandis but C. citriodora, E. camaldulensis, E. cloeziana and E. paniculata are also significant. The latter species yield more charcoal per kilogram than E. grandis but are generally slower growing. Forest managers have long recognised the potential to grow more wood per unit area through the application of tree breeding and more intensive management practices. In Brazil, the company Aracruz Celulose S.A. almost doubled yields from its plantations by species and provenance selection, breeding and the use of clones (Campinhos 1999); the company has 85% of its plantings from clonal cuttings (Bertolucci et al. 1995). Selected clones are also used routinely in eucalypt plantations in the Congo, Morocco and South Africa. Better land preparation, correct use of fertiliser, improved nutrient uptake with selected mycorrhizas and good weed control offer additional opportunities for productivity gains. Domestication of the eucalypts has proceeded faster in countries like Brazil that rely on plantations than in Australia, where industrial wood products have been derived almost entirely from native forests. The countries with long-standing eucalypt plantations (e.g. Brazil, Portugal, Spain, South Africa) are now an important source of eucalypt genotypes adapted for plantation use. Only since the early 1990s have more intensive methods of large-scale eucalypt plantation management been used on a wide scale in Australia, where declining production of wood products from the original native forest and woodland estate due to their

S OCIA L I MPORTA NCE

OF

E UCA LYPTS

C H A P T E R

1

degradation, clearing for agriculture or protection in conservation reserves has resulted in increasing reliance on plantations. Initially exotic Pinus species were planted over large areas in Australia, but increasingly eucalypts are now being planted (O’Connell and Grove 1999). Great economic benefits will accrue from clonal plantations and more intensive management practices. These potential benefits need to be balanced with the increased risks of loss by pests and diseases, fire, frost, storms or nutrient imbalances in plantations with a high value of investment per unit area. In particular, densely planted, uniform-aged plantations with a narrow genetic base are ecologically prone to outbreaks of pests and diseases. However, the greater economic investment and return involved in plantations allows more intensive control of diseases in the plantations, including selection and breeding for disease resistance which could reduce initially damaging diseases to insignificant levels (see Chapters 18 and 22).

1.5 Eucalypts in the rural landscape Population growth has led to a greater demand for fuelwood, poles, paper and other wood products. To meet these needs, forest exploitation has accelerated to unsustainable levels, resulting in degradation of land, forests and woodlands. In countries like India, where fuelwood is the main source of energy for the rural population, there is an annual shortfall in supply. Palanna (1996) states, ‘Today in India there is enough food for people, thanks to the green revolution, but there is not sufficient wood to cook it’. The scale of wood shortages in many countries is such that government-run, larger scale planting programs alone cannot meet the needs. Increasingly, farmers and other land holders are becoming involved in providing wood from new plantings on small farms. Farmers plant trees for a variety of reasons including: 1

shade and shelter

2

wood products

3

non-wood products such as fruit, fodder, honey, chemicals

4

savings and security. 5

D I S E A S E S

A N D

P A T H O G E N S

O F

Although fuelwood derived from prunings and thinnings is an important product, the trees are more valuable as a source of pulpwood, construction wood, poles and posts that can be sold for cash (Kerkhof 1990; Palanna 1996). Tree planting for shade, shelter and the marking of farm boundaries is also important for some farmers. The use of trees for shading crops like coffee and cocoa can provide an important secondary source of income. Trees are also widely used by smallholders as an important source of long-term financial investment, to be harvested when there is a need for cash. Eucalypts have characteristics that can meet most of these requirements and have proved attractive to farmers in many parts of the world. Some rural landscapes in countries such as Ethiopia, China, Vietnam, India and Peru are dominated by eucalypts established mainly by farmers on small holdings. In Ethiopia, farmers plant E. globulus on small areas of land and may subsequently manage the plot to yield a variety of products including leaves and small branches for fuelwood, and poles and posts for house building, fences and other farm uses. Farmers who have insufficient land to have woodlots nevertheless often grow a few trees which can be harvested and sold when they experience food shortages. Many people in Ethiopia are absolutely dependent on eucalypts as a source of fuel and house building material. Eucalypts are a prominent and important part of the rural landscape in southern China. There are largescale plantations as well as dispersed plantings on small farms and on the borders of roads, railways and waterways. In addition to the estimated 600,000 hectares of eucalypt plantations, some one billion individual trees are planted beside farm houses and along roads and waterways (Wang Huoran et al. 1994). The most widely planted species have been E. exserta, C. citriodora, E. globulus and a hybrid of unknown origin referred to as ‘E. leizhou No. 1’ but these are now being replaced by more desirable species such as E. grandis, E. urophylla and hybrids between the two. The eucalypts are favoured because they grow relatively fast and can tolerate the poor, degraded soils of southern China. The wood is used for posts and poles, pulpwood, furniture, farm tools and fuel; essential oils and tannins are extracted from the leaves, and the trees support honey production. Eucalypts are important in crop production by providing shelter from typhoons in coastal areas and 6

E U C A L Y P T S

make a significant contribution to the quality of life and income of the farmers (Zheng Haishui 1988). Eucalypts have been grown on an increasing scale by farmers in India since 1981 and have had a major effect on the rural landscape. As the Indian population approaches one billion, there is an immense requirement for wood for both industrial and domestic use but there is a substantial shortfall in production. The situation is little changed from 1990 when the demand for firewood was 306 million cubic metres and for industrial wood 32 million cubic metres compared with production of only 40 and 12 million cubic metres, respectively (Kumar 1991). Eucalyptus tereticornis, known locally as ‘Eucalyptus hybrid’ or ‘Mysore gum’, is the preferred species for planting in many areas. It is used extensively for village woodlots, on farms and along the boundaries of roads, canals and railways. It has also been planted widely on what are broadly termed ‘wastelands’ or degraded lands. Its popularity is based on its capacity for rapid growth, resistance to cattle browsing, great adaptability to varying environmental conditions, ready market at profitable prices and suitability of the wood for fuel, rural housing and fencing. Farmers have established block plantings and windbreaks on the margins of fields, and sometimes grow eucalypts combined with agricultural crops. Between 1981 and 1988 an estimated eight billion trees were planted on farms, more than 80% of them E. tereticornis, equivalent to about 2.5 million hectares of plantations (Saxena 1991). Eucalypts are often planted to meet future contingencies and have functioned as an important source of savings and long-term investment for the rural poor (Kumar 1991). Economic benefits have generally flowed from eucalypt plantations, although in some areas excessive planting by farmers (e.g. in Haryana and the Punjab) resulted in a local glut of fuelwood and small-sized poles, leading to falling prices. Farmers who planted early made large profits while those planting later did not get similar rewards. In most instances, the trees grown by farmers are to provide products and services to the rural population but there are plantations established by farmers primarily to supply wood to industrial enterprises. In Spain, farmers cooperated with a private pulp and paper company, Celulosas de Asturias, to grow eucalypts on their land for sale to the mill while also making money from the production of honey and essential oils (CEASA 1994). Similar schemes have

E CON OMI C

A ND

operated in Brazil (e.g. de Freitas 1996), the Philippines (Turnbull 1999) and elsewhere. In India, as in some other countries, there is continuing controversy over the use of eucalypts. There are questions about the diversion of crop land from food production to forestry, reduction in employment and the utilisation of common lands for eucalypt growing by the more powerful members of the community. While from the farmer’s or entrepreneur’s viewpoint eucalypt growing makes economic sense, the landless poor may endure increased hardship and reduced welfare when farmers grow eucalypts (Gregersen et al. 1989). Although the debate is frequently framed in terms of the beneficial and negative ecological effects of eucalypts, the major problem relates to land availability, tenure and management (Poore and Fries 1985; Raintree 1996). Hydrological studies of eucalypt plantings show a complex series of interactions, some of which may be seen as beneficial and others as detrimental (Calder 1992). According to an analysis by Raintree and Lantican (1993), ‘the real crux of the political controversy surrounding eucalyptus planting in India was the opportunity cost of a Social Forestry program which generated such dramatic benefits for the relatively better off segments of society while leaving the originally targeted beneficiaries of the Social Forestry program without benefit’. Clearly, if eucalypts are to realise their full potential to provide benefits to a community there will need to be much more careful analysis of ecological and, particularly, social factors before extensive planting programs are undertaken. While the native eucalypt forests and woodlands have always been a valuable source of fuelwood and building and fencing materials for Australian farmers, degradation of the original natural resources has now led to increasing planting of eucalypts on farmland, particularly to help rectify problems of soil degradation and salinity associated with loss of native vegetation (Marcar 1996). Eucalypts, especially E. globulus, are also now becoming an important source of income for farmers in southwest and south-east Australia who grow small plantations in collaboration with forestry companies interested in producing pulpwood (Butcher 1996).

1.6 Conclusion In the first decades of the new millennium, the shortfall in fuelwood and building materials will be

S OCIA L I MPORTA NCE

OF

E UCA LYPTS

C H A P T E R

1

desperate, especially in the densely populated countries of Africa, Latin America, and South and East Asia where much of the natural forest has disappeared or is severely degraded. Consumption of fuelwood and poles will increase substantially and natural forest will continue to be degraded by unsustainable harvesting or lost to agriculture. Trees, including eucalypts, will be critically important in providing wood products and assisting sustainable agriculture on the more marginal lands in these countries. Large-scale plantations of eucalypts in many countries, including Australia, will continue to supply a large proportion of the pulp used for paper manufacture, the demand for which continues to expand. The management of these plantations will continue to intensify with increasing selection of highly productive genotypes, clonal propagation, attention to land preparation, use of fertilisers, and use of intensive disease control measures, particularly selection and breeding of disease-resistant genotypes. Eucalypts, because of their adaptation to a wide range of environments, fast growth, ease of management, and the valuable properties of their wood and pulp, will continue to have a major and often expanding role in providing wood products, improved standards of living and environmental protection in many countries.

1.7 References Aracruz Celulose (1991). Aracruz Celulose S.A., Brazil, Annual Report 1990. Aracruz Celulose, Brazil. Australian Bureau of Agricultural and Resource Economics (1997). Australian Forest Products Statistics. June Quarter 1997. ABARE Project 1116. (Australian Bureau of Agricultural and Resource Economics: Canberra.) Australian Bureau of Agricultural and Resource Economics (1999). Forest products: outlook in regional markets to 2003–04. Australian Commodities, Forecasts and Issues 6, 91–102. Australian Forestry Council (1989). Australian Forest Resources Present Areas and Estimates of Future Availability. (Forestry Resources Committee of the Australian Forestry Council: Canberra.) Bazett, M.D. (1993). Industrial Wood. Study No. 3. Shell/ World Wide Fund For Nature Tree Plantation Review. (Shell and WWF: London.) Bertolucci, F.L.G., Demuner, B.J., Garcia, S.L.R. and Ikemori, Y.K. (1995). Increasing fiber yield and quality at Aracruz. In Eucalypt Plantations: Improving Fibre Yield and Quality. Proceedings of the CRCTHF–IUFRO Conference, Hobart, 19–24

7

D I S E A S E S

A N D

P A T H O G E N S

O F

February 1995. (Eds B.M. Potts, N.M.G. Borralho, J.B. Reid, R.N. Cromer, W.N. Tibbits and C.A. Raymond) pp. 31–34. (Cooperative Research Centre for Temperate Hardwood Forestry: Hobart.) Bouillet, J.P., Nzila, J.D., Ranger, J., Laclau, J.P. and Nizinski, G. (1999). Eucalyptus plantations in the Equatorial Zone, on the coastal plains of Congo. In Site Management and Productivity in Tropical Plantation Forests. (Eds E.K.S. Nambiar, C. Cossalter and A. Tiarks) pp. 13–21. (Center for International Forestry Research: Bogor, Indonesia.) Butcher, G. (1996). Establishment of a major hardwood resource in Western Australia. In Environmental Management: The Role of Eucalypts and Other Fast Growing Species. (Eds K.G. Eldridge, M.P. Crowe and K.M. Old) pp. 146–151. (CSIRO Division of Forestry and Forest Products: Canberra.) Calder, I.R. (1992). Water use of eucalypts—a review. In Growth and Water Use of Forest Plantations. (Eds I.R. Calder, R.L. Hall and P.G. Adlard) pp. 167–179. (J. Wiley: New York.) Campinhos, E. (1999). Sustainable plantations of high yield Eucalyptus trees for production of fiber: the Aracruz case. New Forests 17, 129–143. Carron, L.T. (1985). The History of Forestry in Australia. (Australian National University Press: Canberra.) CEASA (1994). Intelligent fibre. World Paper. Nov./Dec. 1994. 2 pp. Commonwealth of Australia (1997). Australia’s First Approximation Report for the Montreal Process. (Department of Primary Industries and Energy: Canberra.) Cromer, R., Smethurst, P., Turnbull, C., Misra, R., LaSala, A., Herbert, A. and Dimsey, L. (1995). Early growth of eucalypts in Tasmania in relation to nutrition. In Eucalypt Plantations: Improving Fibre Yield and Quality. Proceedings of the CRCTHF–IUFRO Conference, Hobart, 19–24 February 1995. (Eds B.M. Potts, N.M.G. Borralho, J.B. Reid, R.N. Cromer, W.N. Tibbits and C.A. Raymond) pp. 331–335. (Cooperative Research Centre for Temperate Hardwood Forestry: Hobart.) Davidson, J. (1995). Ecological aspects of Eucalyptus plantations. In Proceedings of the Regional Expert Consultation on Eucalyptus, Vol. I, pp. 35-72. RAPA Publication 1995/6. (Food and Agriculture Organization Regional Office for Asia and the Pacific: Bangkok.) de Freitas, M. (1996). Planted forests in Brazil. In Caring for the Forest: Research in a Changing World. IUFRO XX World Congress, Tampere, Finland, 6–12 August 1995. Congress Report, Vol. II, pp. 147–154. (International Union of Forestry Research Organizations: Tampare, Finland.) EMBRAPA (1996). Brasil tem banco estrategico de eucalipto. Folha da Floresta No. 8, 6–8.

8

E U C A L Y P T S

Food and Agriculture Organization (1991). Wood and Wood Products. Forestry Statistics Today for Tomorrow. 1961–89 to 2010. (Food and Agriculture Organization: Rome.) Food and Agriculture Organization (1993). Forest Resources Assessment 1990: Tropical Countries. Food and Agriculture Organization Forestry Technical Paper 112. (Food and Agriculture Organization: Rome.) Gregersen, H., Draper, S. and Elz, D. (1989). People and Trees—The Role of Social Forestry in Sustainable Development. (The World Bank: Washington DC.) Hillis, W.E. and Brown, A.G. (Eds) (1983). Eucalypts for Wood Production. 2nd edn. (CSIRO: Melbourne.) Iuseum, A.N., Correa de Lima, J.P. and Mercado, R.S. (1988). Brazil: the forest sector’s participation in international trade. In International Trade in Forest Products. (Ed. A. Nagy) pp. 37–46. (A.B. Academic Publishers: Bicester, UK.) Kerkhof, P. (1990). Agroforestry in Africa: a Survey of Project Experience. (Eds G. Foley and G. Bernard). (Panos: London.) Kerruish, C.M. and Rawlins, W.H.M. (Eds) (1991). The Young Eucalypt Report—Some Management Options for Australia’s Regrowth Forests. (CSIRO: Melbourne.) Kile, G.A. (1999). Planted forests for food, fibre, fuel and fulfillment. Paper to the Crawford Fund Seminar on The Food and Environment Tightrope, 24 November 1999, Canberra, Australia. Kumar, V. (1991). Eucalyptus in the forestry scene of India. In Proceedings of IUFRO Symposium on Intensive Forestry: The Role of Eucalypts. Durban, September 1991. (Ed. A.P.G. Schönau) Vol. 2, pp. 1105–1116. (South African Institute of Forestry: Pretoria, South Africa.) Marcar, N.E. (1996). Eucalypts for salt-affected and acid soils. In Environmental Management: The Role of Eucalypts and Other Fast Growing Species. (Eds K.G. Eldridge, M.P. Crowe and K.M. Old) pp. 90–99. (CSIRO Division of Forestry and Forest Products: Canberra.) Nambiar, E.K.S. and Brown, A.G. (1997). Management of Soil, Nutrients and Water in Tropical Plantations. ACIAR Monograph No. 43. (Australian Centre for International Agricultural Research: Canberra.) O’Connell, A.M. and Grove, T.S. (1999). Eucalypt plantations in south-western Australia. In Site Management and Productivity in Tropical Plantation Forests. (Eds E.K.S. Nambiar, C. Cossalter and A. Tiarks) pp. 53–59. (Center for International Forestry Research: Bogor, Indonesia.) Palanna, R.M. (1996). Eucalyptus in India. In Reports Submitted to the Regional Expert Consultation on Eucalyptus. Vol. II, pp. 46–57. RAP Publication 1996/ 44. (FAO Regional Office for Asia and the Pacific: Bangkok.)

E CON OMI C

A ND

Poore, M.E.D. and Fries, C. (1985). The Ecological Effects of Eucalyptus. Food and Agriculture Organization Forestry Paper No. 59. (Food and Agriculture Organization: Rome.) Pousajja, R. (1996). Eucalypt plantations in Thailand. In Reports Submitted to the Regional Expert Consultation on Eucalyptus. Vol. II, pp. 213–223. RAP Publication 1996/44. (FAO Regional Office for Asia and the Pacific: Bangkok.) Raintree, J.B. (1996). The great Eucalyptus debate: what is it all about? In Reports Submitted to the Regional Expert Consultation on Eucalyptus. Vol. II, pp. 64–74. RAP Publication 1996/44. (FAO Regional Office for Asia and the Pacific: Bangkok.) Raintree, J.B. and Lantican, C. (1993). Forestry economics research and MPTS development. In Forestry Economics Research in Asia. (Eds Songkram Thammincha, Ladawan Puangchit and H. Wood) pp. 15–31. (Faculty of Forestry, Kasetsart University: Thailand and IDRC: Canada.) Resource Assessment Commission (1991). Forest and Timber Inquiry. Draft Reports Vols 1 and 2. (Resource Assessment Commission, Australian Government Publishing Service: Canberra.) Resource Assessment Commission (1992). Forest and Timber Inquiry. Final Report. Vols 1, 2A and 2B. (Resource Assessment Commission, Australian Government Publishing Service: Canberra.) Rolo, L.B. (1988). The outlook of the Portuguese pulp industry. In Global Issues and Outlook in Pulp and Paper. (Ed. G.F. Schreuder) pp. 142–150. (University of Washington Press: Seattle.) Saxena, N.C. (1991). Marketing constraints for Eucalyptus in farmlands in India. Agroforestry Systems 13, 73–85. Tran Xuan Thiep (1996). Eucalyptus plantations in Vietnam: their history and development process. In Reports Submitted to the Regional Expert Consultation on Eucalyptus. Vol. II, pp. 254–277. RAP Publication 1996/44. (FAO Regional Office for Asia and the Pacific: Bangkok.) Turnbull, J.W. (1991). Future use of Eucalyptus: opportunities and problems. Proceedings of IUFRO Symposium on Intensive Forestry: The Role of Eucalypts. Durban, September 1991. (Ed. A.P.G.

S OCIA L I MPORTA NCE

OF

E UCA LYPTS

C H A P T E R

1

Schönau) Vol. 1, pp. 2–27. (South African Institute of Forestry: Pretoria, South Africa.) Turnbull, J.W. (1996). Biodiversity in Australian forest ecosystems. In Caring for the Forest: Research in a Changing World. IUFRO XX World Congress, Tampere, Finland, 6–12 August 1995. Congress Report, Vol. II, pp. 90–99. (International Union of Forestry Research Organizations: Tampere, Finland.) Turnbull, J.W. (1999). Eucalypt plantations. New Forests 17, 37–52. Wang Huoran, Jiang Zeping and Yan Hong (1994). Australian trees grown in China. In Australian Tree Species Research in China. (Ed. A.G. Brown) pp. 19–25. ACIAR Proceedings No. 48. (Australian Centre for International Agricultural Research: Canberra.) Wells, K.F. (1991). The young eucalypt resource. In The Young Eucalypt Report. (Eds C.M. Kerruish and W.H.M. Rawlins) pp. 19–27. (CSIRO: Melbourne.) Wells, K.F., Wood, N.H. and Laut, P. (1984). Loss of forests and woodlands in Australia: A summary by State based on rural local government areas. CSIRO Division of Water and Land Resources Technical Memorandum 84/4. (CSIRO: Canberra.) Werren, M. (1991). Eucalyptus plantation development in Sumatra. In Proceedings of IUFRO Symposium on Intensive Forestry: The Role of Eucalypts. Durban, September 1991. (Ed. A.P.G. Schönau) Vol. 2, pp. 1160–1166. (Southern African Institute of Forestry: Pretoria, South Africa.) Wood, M., Howell, C. and Jones, M. (1999). Australia’s national plantation inventory: an interim update. In Australian Forest Products Statistics, September Quarter, pp. 1–2. (Australian Bureau of Agricultural and Resource Economics: Canberra.) World Resources Institute (1998). Aracruz Celulose S.A. and Riocell S.A.: efficiency and sustainability on Brazilian pulp plantations. In The Business of Sustainable Forestry: Case Studies. pp. 5–1 to 5–31. (The John D. and Catherine T. MacArthur Foundation: Chicago.) Zheng Haishui (1988). The role of Eucalyptus plantations in southern China. In Multipurpose Tree Species for Small-Farm Use. (Eds D. Withington, K.D. MacDicken, C.B. Sastry and N.R. Adams) pp. 79–85. (Winrock International and IDRC: Canada.)

9

This Page Intentionally Left Blank

C H A P T E R

M ORPHOLOGY , P HYLOGENY , O RIGIN , D ISTRIBUTION AND G ENETIC D IVERSITY E UCALYPTS

OF

2

B.M. Potts and L.A. Pederick

S

U M M A R Y

Eucalypts are an assemblage of mainly tree species in the myrtaceous genera Eucalyptus, Corymbia and Angophora. They are generally long-lived, evergreen species that include some of the very tall, fast-growing hardwood species now in great demand for planting around the world. Most are endemic to Australia, with a few species extending into islands to the north, and have evolved largely in isolation in Australia. From north to south, the climate of the vast Australian continent changes from summer to winter rainfall and from warm to cooler seasons which, combined with the effect of variations in altitude, aspect and soils, has resulted in an immense diversity of habitats to which eucalypts have adapted. They show exceptional differentiation and there are often large genetic differences. This variation provides the basis for selection and breeding of variants adapted to a wide range of plantation environments. There are many examples of genetic variation in susceptibility to disease both between and within species and this variation can be exploited for disease management.

11

D I S E A S E S

A N D

P A T H O G E N S

O F

E U C A L Y P T S

2.1 Introduction Eucalypts belong to the predominantly southern hemisphere family, Myrtaceae (Johnson and Briggs 1984) and have traditionally encompassed the more than 700 species in the genus Eucalyptus L’Hér., as well as the 11 closely related taxa in the genus Angophora Cav. (Pryor and Johnson 1971; Pryor 1976; Pryor and Johnson 1981; Brooker and Kleinig 1994; Hill and Johnson 1995; Ladiges et al. 1995). Angophora has flowers with free sepals and petals whereas in Eucalyptus, with only rare exceptions, these are fused to form one or two opercula which cover the numerous stamens and single style (Ladiges 1997). The eucalypts are virtually all endemic to Australia and together with the monotypic genus Arillastrum from New Caledonia, form the Eucalyptus alliance (subfamily Leptospermoideae) of Johnson and Briggs (1984).

2.2 Morphology Eucalypts are generally long-lived, forest (30–50 m) or woodland (10–25 m) trees, or mallees (several stems 1–10 m high emerging from a common underground woody stock) (Pryor 1976). The genus Eucalyptus contains the tallest hardwood species in the world, E. regnans, which grows in the mountains of Victoria and Tasmania and has attained heights over 100 metres (Mace 1996). Other species such as E. deglupta, E. diversicolor and E. viminalis may grow to more than 70 metres (Boland et al. 1985). At the other extreme, some species are mere shrubs (e.g. E. vernicosa, Potts and Jackson 1986; E. fruticosa, Brooker and Kleinig 1994). Eucalypts are evergreen, except for several northern Australian species that shed most of their leaves during the northern dry season (e.g. Corymbia confertiflora; Brooker and Kleinig 1994). Species exhibit large differences in form, habit, reproductive and foliage characteristics. The foliage may also change dramatically through ontogeny (heteroblasty), with leaf morphology, anatomy, surface waxes, phyllotaxis and orientation often changing considerably between seedling (up to about the 10th node), juvenile and adult stages (Fig. 2.1; Boland et al. 1985; Brooker and Kleinig 1990a; Wiltshire et al. 1991; Hill and Johnson 1995). Ontogenetic changes may also occur in physiology (Cameron 1970; Battaglia and Reid 1993), leaf chemistry (Li et al. 1995), pest (autumn gum moth; Farrow et al. 1994) and disease susceptibility

12

Figure 2.1

Branch showing juvenile (larger, lower) and adult (narrow, uppermost) leaves of Eucalyptus globulus ssp. globulus.

(e.g. to Mycosphaerella (M.) spp., see Chapter 9). In some species (e.g. E. cinerea, E. perriniana, E. risdonii), the juvenile foliage type is maintained at reproductive maturity. While many species have a persistent dead outer bark, ranging in appearance from fibrous (‘stringy bark’) to scaly (‘box bark’), the bark of others is decorticating, resulting in smooth stems (‘gum bark’) of variable colour (Boland et al. 1985; Brooker and Kleinig 1990a, 1990b; Brooker and Kleinig 1994). The bark often protects numerous dormant vegetative buds. These sprout to form masses of leafy shoots (epicormic shoots) over the trunk and branches after trees are defoliated or damaged by fire (Fig. 2.2), drought or pests (Jacobs 1955; Pryor 1976). Eucalypts have very efficient mechanisms of branch shedding and occlusion of the resulting wound (Jacobs 1955). A protective layer of tannins or resins is deposited around the part of the moribund branch already included in the stem and kino may be secreted over branch stubs resulting in protection from fungal attack. Most species also

M O RP HO LO GY , P HYL OGENY , O R IGIN , D IST R I BU T I ON

A ND

G ENE TIC D IVE RSITY

Figure 2.3 Figure 2.2

A tree of Eucalyptus globulus ssp. globulus regenerating from epicormic shoots following wildfire.

have an unusual organ, the lignotuber, which develops as swellings in the axils of the cotyledons and sometimes the first few seedling leaves and comprises a mass of vegetative buds, vascular tissue and food reserves (Jacobs 1955; Pryor 1976; Fig. 2.3). The lignotuber generally becomes buried and is extremely important in survival where drought and fire are frequent, allowing plants (particularly seedlings) to regenerate after death or damage to the main stem. Continual damage to mature plants may result in the development of the mallee habit and large, clonal copses from underground lignotubers (Lacey and Johnston 1990; Kennington and James 1997). Other vegetative regeneration mechanisms, such as rhizomes or root suckering, are rare (Lacey 1974; Lacey and Johnston 1990; Hill and Johnson 1995). Regeneration is usually from seed which is

OF

E UCA LYPTS

C H A P T E R

2

Lignotubers developing on a sapling of Eucalyptus risdonii. Stem diameter immediately above the basal lignotuber is about 1.5 centimetres.

stored in woody, fire-protected capsules in the canopy and shed in mass, especially following wildfire (Boland et al. 1980). Seeds generally have no special mechanisms for dispersal, apart from the terminally winged seed of the red bloodwoods. Except for a few cases of water dispersal (e.g. E. camaldulensis) and a single report of bee dispersal (Wallace and Trueman 1995), seed dispersal is mainly by wind and gravity and normally occurs over short distances (Potts and Wiltshire 1997). The eucalypt flower is normally bisexual (Fig. 2.4), although rare male sterile individuals have been reported (Pryor 1976; Ellis and Sedgley 1993). The numerous stamens and the perigynous arrangement of the outer floral whorls are characteristic of the Myrtaceae. However, the operculum is unique to the group although its derivation differs and it appears

13

D I S E A S E S

Figure 2.4

A N D

P A T H O G E N S

O F

Flowers of Eucalyptus globulus ssp. globulus showing the inner operculum just about to be shed (right) and fully expanded anthers (left).

to have evolved independently several times (Ladiges 1997). The eucalypt flowers are occasionally solitary (e.g. E. globulus, Fig. 2.4), but generally occur in clusters of regular numbers of 3, 5, 7, 11, 15 or more in an inflorescence, which is effectively a reduced dichasial cyme, but is often called an ‘umbel’ (Johnson 1972; Pryor 1976). Flower clusters may arise singly in the leaf axils (simple axillary inflorescence), as paired axillary inflorescences or compound axillary or terminal inflorescences (Brooker and Kleinig 1990a), with the compound inflorescences developing in a manner unique to eucalypts (Pryor 1976). At anthesis, the operculum is shed and the stamens spread, resulting in a conspicuous floral display (House 1997). Pollination is undertaken by a variety of insects, birds and marsupials (Pryor 1976; Eldridge et al. 1993; House 1997; Potts and Wiltshire 1997). Eucalypts are generally preferential outcrossers with high levels of outcrossing maintained by protandry and various prezygotic and postzygotic barriers to self fertilisation (Pryor 1976; Potts and Wiltshire 1997), coupled with intense, post-dispersal selection against the products of self fertilisation in the regenerating forest (Hardner and Potts 1997).

2.3 Phylogeny As originally defined, the eucalypts are not a natural grouping of taxa. From the early 1990s there has been a major change from a classical to cladistic

14

E U C A L Y P T S

Figure 2.5

Proposed phylogenetic relationships in the Eucalyptus alliance (after Ladiges 1997).

based, phylogenetic treatment of the group (reviewed in Hill and Johnson 1995; Ladiges 1997). In an informal but widely used classification of eucalypts, Pryor and Johnson (1971) divided Eucalyptus into seven subgenera (Corymbia, Blakella, Eudesmia, Gaubaea, Idiogenes, Monocalyptus, Symphyomyrtus), with the genus Angophora considered of equal rank. An eighth subgenus (Telocalyptus) comprising four tropical eucalypts with truly terminal inflorescences (E. deglupta, E. howittiana, E. raveretiana, E. brachyandra) was later suggested by Johnson (1976). Johnson (1976) subsequently proposed that the eucalypts (and Angophora) be rearranged into nine groups or genera (one of which would retain the name Eucalyptus) and these would have about the same degree of distinctness as existed between Eucalyptus and Angophora. Pryor and Johnson (1981) later suggested that the bloodwoods (Blakella and Corymbia) were more closely related to Angophora than to the rest of Eucalyptus and that the eucalypts were polyphyletic, comprising three major evolutionary lineages (or suballiances): 1

Arillastrum, Angophora, Blakella and Corymbia

2

Symphyomyrtus, Telocalyptus and Eudesmia

3

Monocalyptus, Idiogenes and Gaubaea.

The most recent view of eucalypt phylogeny, which is relatively consistent across morphological (Hill and Johnson 1995; Ladiges et al. 1995) and molecular (Sale et al. 1993; Hill and Johnson 1995; Ladiges et al. 1995; Urdovic et al. 1995; Sale et al.

M O RP HO LO GY , P HYL OGENY , O R IGIN , D IST R I BU T I ON

TA BLE 2. 1

A ND

G ENE TIC D IVE RSITY

OF

E UCA LYPTS

C H A P T E R

2

Summary of the key characters differentiating Angophora, Corymbia and the major subgenera of Eucalyptus

After Ladiges (1997) with minor additions from Brooker and Kleinig (1994) and Hill and Johnson (1995). Characteristics of the minor Eucalyptus subgenera Gaubaea, Idiogenes and Telocalyptus are given in Ladiges (1997).

Group

No. of taxa

Angophora/ bloodwood lineage

Characteristics Pinnate venation; raised oil glands (bristle glands) with 4 cap cells of raised oil glands with micropapillae (conspicuous in seedlings); oxalate crystals in embryonic cotelydons; stemonophore absent; pith oil ducts; solitary vessels in the xylem; hemitropous ovules not in regular rows; seed with 2 integuments

Angophora

11–13

Free sepals and petals; corymbioid inflorescences; mop-like stigma with long papillae; pinnate venation; opposite disjunct phyllotaxy; multicellular hairs; cotyledons large and unfolded in embryo; fruits with ridges

Corymbia

113

Calycine operculum; stigmas mop-like or tapering with short papillae; conflorescences terminal corymbioid to axillary; stigmas mop-like with long papillae or tapering with short papillae; opposite disjunct phyllotaxy but alternate adult leaves; unicellular hairs associated with raised oil glands; cotyledons entire, either folded in embryo or not; fruits woody or thin walled

600+

Sepals and petals free or flowers with 1 or 2 opercula; taxa with corolline operculum develop a stamonophore; adult leaves usually with wide spaced, more irregular secondary veins than bloodwoods; opposite disjunct phyllotaxy; if present raised oil glands have 3 cap cells and no micropapillae; stigmas usually with relatively short papillae; regular arrangement of ovules in vertical rows on the placenta; embryos with folded, emarginate or bilobed cotyledons; fruits woody

Subgenus Eudesmia

20

Free sepals (sometimes not obvious); corolline operculum; in some species stemonophore lobed and stamens appear to be in 4 bundles; some subgroups with characteristic hairs radiating from oil glands; hemitropous ovules in 2–4 rows per loculus; seed with 2 integuments

Subgenus Monocalyptus

120+

Single operculum (thought to be derived from petals, lacking sepals); stemophore; axillary conflorescences; anatropous ovules; usually in 2 rows per loculus; seed with 2 integuments; lacking crystalliferous layer in outer integument; reniform cotyledons

Subgenus Symphyomyrtus

300+

Calycine and corolline operculum; stemophore; conflorescences usually axillary; hemitropous ovules in 4–10 rows; seed with 1 integument; emarginate cotyledons

Eucalyptus s. str. lineage

1996) studies, is of two major lineages, one including Angophora, subgenus Corymbia (bloodwoods) and subgenus Blakella (paper fruited bloodwoods or ghost gums), and the other comprising all other subgenera of Eucalyptus (Fig. 2.5). The subgenera Corymbia and Blakella of Pryor and Johnson (1971) have now been formally separated from the rest of Eucalyptus in a new genus, Corymbia K.D.Hill and L.A.S.Johnson (Hill and Johnson 1995), containing 113 species. A detailed classification of these species is provided by Hill and Johnson (1995). Key characteristics of Angophora, Corymbia and Eucalyptus s. str. (and subgenera) are summarised in Table 2.1. In the non-bloodwood eucalypts (Eucalyptus s. str.), the adult leaves have opposite disjunct phyllotaxis,

but with secondary venation more widely spaced and more irregular than in the bloodwoods (Ladiges 1997; Table 2.1). In Eucalyptus, the sepals and/or the petals are also fused into one or two opercula, which appear to have evolved independently from that in the bloodwoods. Within the non-bloodwood eucalypts, three major lineages are recognised (see Ladiges et al. 1995; Ladiges 1997; Fig. 2.5): 1

Eudesmia (eudesmids)

2

Monocalyptus (monocalypts)

3

Symphyomyrtus (symphyomyrts).

The Symphyomyrtus lineage is characterised by the seed coat comprising one integument, rather than two (Table 2.1). Virtually all species have two

15

D I S E A S E S

A N D

P A T H O G E N S

O F

Transversaria Maidenaria Exsertaria Adnataria Dumaria Bisectaria Figure 2.6

Proposed phylogenetic relationship among the major sections in the subgenus Symphyomyrtus (after Chappill and Ladiges 1996; Ladiges 1997).

opercula, although they may be closely fused in some species (e.g. section Adnataria, boxes and iron barks) (Pryor and Johnson 1971). Symphyomyrtus is the largest subgenus and includes more than 300 species in six major sections (Fig. 2.6). Most species used in plantation forestry, particularly outside Australia, are from Pryor and Johnson’s (1971) sections Maidenaria (e.g. E. globulus, E. nitens, E. viminalis), Exsertaria (northern and eastern red gums) (e.g. E. camaldulensis, E. tereticornis) and Transversaria (eastern blue gums, red mahoganies, grey gums) (e.g. E. diversicolor, E. saligna, E. grandis, E. urophylla) (Eldridge et al. 1993). The Monocalyptus lineage includes the subgenera Gaubaea, Idiogenes and Monocalyptus. It is characterised by ovules being orientated with the micropile facing the placenta (anatropous) and arranged in two or rarely four rows, and seeds which do not have a crystalliferous layer (Ladiges 1997). The subgenus Gaubaea comprises two species, E. curtisii and E. tenuipes, which have unique features. This subgenus may not be monophyletic and a separate subgenus for E. curtisii has been suggested (Brooker and Kleinig 1994). The subgenus Idiogenes consists only of E. cloeziana, which appears to be the sister taxon to the subgenus Monocalyptus. These three species have small free sepals. In the subgenus Monocalyptus, the sepals are believed to be reduced or absent and the subgenus is characterised by a single operculum derived from

16

E U C A L Y P T S

early fusion of the petals (Drinnan and Ladiges 1989, cf. Pryor and Knox 1971). Monocalyptus is the second largest subgenus and includes groups commonly known as the peppermints (Ladiges et al. 1983), mahoganies, stringy barks (Ladiges and Humphries 1986) and green (Ladiges et al. 1989) and blue (Ladiges et al. 1992) ashes. Many of the monocalypts are important timber species, at least in native forests in Australia (e.g. E. delegatensis, E. diversifolia, E. fastigata, E. obliqua, E. regnans; Eldridge et al. 1993). Cladistic studies of the various Monocalyptus subgroups are reviewed by Ladiges (1997).

2.4 Origins The eucalypt fossil record is reviewed in Hill (1994), Rozefelds (1996) and Ladiges (1997). The ancestors of the Myrtaceae are thought to have migrated into the Australian region of Gondwana from Antarctica, as myrtaceous-like pollen in sediments of the Antarctic Peninsula from the Late Cretaceous [about 90–65 million years ago (MYa)] appears to predate the earliest New Zealand and Australian records from the Paleocene (65–55 MYa) (Dettmann 1994; Specht 1996). This migration was followed by an explosion of myrtaceous genera through the Tertiary, with most extant genera now occurring in the Australasian–Oceanian region and Central and South America (Johnson and Briggs 1981; Johnson and Briggs 1984; Specht 1996). Eucalypts are thought to have evolved from a rainforest or rainforest margin ancestor (Gill et al. 1985; Brooker 1986; Eldridge et al. 1993). Australia has traditionally been accepted as the place of origin and diversification of eucalypts (Carr 1973; Pryor 1976; Pryor and Johnson 1981) and Barlow (1981) considers they originated at least 40 million years ago, in the early Tertiary, on the fragment of Gondwana that formed Australia. This view was held because of the almost total restriction of the extant distribution to Australia, the distribution of related genera in New Guinea and New Caledonia, and the lack of fossil evidence from other countries. However, there are now several reports of eucalyptlike macrofossils occurring in Patagonia, South America (Miocene or Eocene; Frenguelli 1953) and Central Otago, New Zealand (Early Miocene; Pole 1989; Pole 1993 ) which, if correct, provide the first clues that eucalypts may not have been restricted to Australia (Fig. 2.7) and may have a more ancient

M O RP HO LO GY , P HYL OGENY , O R IGIN , D IST R I BU T I ON

Figure 2.7

A ND

G ENE TIC D IVE RSITY

OF

E UCA LYPTS

C H A P T E R

2

The natural distribution of: a) Angophora, b) Corymbia, and the Eucalyptus s. str. subgenera c) Eudesmia, d) Idiogenes and Gaubaea, e) Monocalyptus and f) Symphyomyrtus. Subgenera follow Pryor and Johnson (1971) whereas Corymbia and Angophora follow Hill and Johnson (1995).

17

D I S E A S E S

A N D

P A T H O G E N S

O F

origin. In both cases, the fossils appear to be Symphyomyrtus-like. An ancient, extra-Australian distribution is given further credence by the finding of fossils of another typically Australian group, the she-oaks (Casuarinaceae), in South America and in New Zealand (with the eucalypt fossils); as for Eucalyptus, this group is presently absent from both regions (Hill and Carpenter 1990). Acacia, Casuarina and Eucalyptus-like pollen has also been recorded in Miocene–Early Pleistocene deposits in New Zealand (Mildenhall 1980), suggesting relatively recent extinction of these taxa in New Zealand (Hill 1994). The oldest eucalypt-like macrofossils in Australia appear to be fruits from a Palaeocene or Eocene (65–35 MYa) deposit in south-east Queensland that have affinities to Corymbia or Angophora (Rozefelds 1996). Although evidence is still sparse, eucalypts are believed to have been components of the more xeric vegetation in the interior of Australia during the Early Tertiary (Lange 1982; Martin 1982; Hill 1994). The frequent periods of aridity through the Miocene resulted in expansion of the xerophytic components of the Australian flora and evolution and diversification of xerophytic genera such as Eucalyptus (Martin 1978; Barlow 1981; Martin 1982; Specht 1996; Wardell-Johnson et al. 1997). With the progression of aridity in central Australia, eucalypts were displaced to the continental margins. Indeed, Victorian and New South Wales macrofossil deposits are consistent with a mosaic of eucalypt/ sclerophyllous and rainforest communities in southeast Australia during the Miocene (Holmes et al. 1983; Pole et al. 1993). However, pollen records suggest that the modern eucalypt flora did not become widespread until the Pleistocene (5–1.5 MYa; Martin 1981; Kershaw et al. 1994). The dominance of the Australian landscape by eucalypts appears to be relatively recent. The increase in eucalypt pollen over this period is associated with increased levels of charcoal, suggesting that the genus has undertaken a major spatial radiation in about the last 200,000 years as a response to increasing fire frequency due to the arrival of humans in Australia, coupled with increasing aridity and a remarkable preadaptation to fire (Singh et al. 1981; Kershaw 1986; Hill 1994). An important factor in the evolution of eucalypts is believed to be their adaptation to the nutrient-poor soils of the ancient land surfaces that dominate much

18

E U C A L Y P T S

of the Australian continent (Eldridge et al. 1993). Less oligotrophic environments appear to have become available to eucalypts only after the area of closed forest was reduced by climatic and other changes. Within Corymbia, for example, taxa with the more derived characters tend to occur on less nutrient-deficient soils (Hill and Johnson 1995). Late Miocene (5–10 MYa) fossils from Bacchus Marsh, Vic., provide the first unequivocal evidence of the subgenus Monocalyptus, as well as Symphyomyrtus (Ladiges 1997). However, biogeographical evidence would suggest that the divergence of Monocalyptus and Symphyomyrtus (Specht 1996), and even major lineages within Monocalyptus (Ladiges and Brooker 1987) and the genus Corymbia (Hill and Johnson 1995, p. 210), had occurred much earlier, prior to the Eocene–Miocene marine transgressions into the Eucla and Murray Basins and continental drying that would have isolated eastern and western floras. Geographical isolation appears to have been important in speciation within the genus (Pryor 1976; Pryor and Johnson 1981; Brooker and Hopper 1991; Ladiges 1997). The species of the south-west of Western Australia, particularly from the wetter zones, are very distinct from those of the eastern half of the continent. Most of the south-western species are endemic and have decorative features, including coloured stamens and large sculptured fruits, which are almost absent in eastern Australian species (Brooker and Kleinig 1990b).

2.5 Distribution Only five tropical eucalypts are endemic to areas outside Australia—C. papuana, E. deglupta, E. orophila, E. urophylla and E. wetarensis (Hill and Johnson 1995; Pryor et al. 1995; Ladiges 1997). A small group of species of Symphyomyrtus (E. alba, E. brassiana, E. tereticornis) and Corymbia (C. disjuncta, C. latifolia, C. novoguinensis, C. tessellaris) also extend outside Australia into Papua New Guinea (Chippendale 1988; Hill and Johnson 1995). The latter occurrences are northerly extensions of Australian populations on Cape York Peninsula, which were no doubt continuous across Torres Strait during periods of lower sea levels (Carr 1973; Pryor 1976). Corymbia papuana is endemic to the southern parts of the island of New Guinea and is closely related to the newly described species C. paracolpica from Cape York Peninsula (Hill and

M O RP HO LO GY , P HYL OGENY , O R IGIN , D IST R I BU T I ON

A ND

Johnson 1995), previously considered conspecific with C. papuana (Brooker and Kleinig 1994). Eucalyptus urophylla and the two recently described species, E. orophila and E. wetarensis, occur in Timor and adjoining islands of the Lesser Sunda Islands (House and Bell 1994; Pryor et al. 1995). These three species are related to Australian species such as E. pellita which occurs on Cape York Peninsula (Pryor and Johnson 1981). In contrast, E. deglupta is unlike any other Australian eucalypt. Eucalyptus deglupta is the species with the most northerly distribution, has extremely large disjunctions through its geographical range and has apparently evolved in isolation from the Australian eucalypts. It occurs in northern New Guinea and New Britain in Papua New Guinea, on the Indonesian islands of Sulawesi and Ceram and in the southern Philippines (Eldridge et al. 1993). Cataclysmic wind dispersal is one explanation for the eucalypt distributions that occur beyond the stable edge of the Australian continent (Carr 1973; Pryor and Johnson 1981). However, Ladiges (1997) argues that they could be explained by geological events during the Miocene (for E. deglupta) and Pliocene (e.g. for E. urophylla). Within Australia, eucalypts are ubiquitous and dominate nearly all types of vegetation except rainforest, central arid and high montane vegetation (Pryor 1976; Pryor and Johnson 1981; Specht 1996; Wardell-Johnson et al. 1997). They occur from sea level to the alpine tree line, from high rainfall to semiarid zones, and from the tropics to latitudes as low as 42° south (Pryor and Johnson 1981; Specht 1996; Wardell-Johnson et al. 1997). They occur in tall forest above developing rainforest understoreys in both tropical (e.g. C. torelliana, E. deglupta, E. urophylla) and temperate (e.g. E. obliqua, E. regnans; Jackson 1968) regions. They are the dominant component of open forests and woodlands throughout Australia, and in lower rainfall areas the mallees, with low multistemmed habit and large woody lignotubers, predominate. Several species also extend into the central, arid zone of Australia (e.g. E. rameliana; Sampson et al. 1995), where they may be confined to watercourses (e.g. E. camaldulensis, E. microtheca) or rock outcrops (e.g. E. crucis) (Brooker and Kleinig 1990b). However, while usually originating from Australia, eucalypts are now widely planted throughout the world for timber, fuel and pulp production, and land races and even

G ENE TIC D IVE RSITY

OF

E UCA LYPTS

C H A P T E R

2

stabilised hybrids have developed in many countries (Eldridge et al. 1993). The natural distributions of Angophora, Corymbia and the major subgenera of Eucalyptus s. str. are shown in Figure 2.7. Monocalyptus species are restricted to the east, south-east and south-west regions and appear to be more competitive than Symphyomyrtus species on less fertile sites (Florence 1981; Pryor and Briggs 1981; Wardell-Johnson et al. 1997). The subgenus Monocalyptus and the section Maidenaria of the subgenus Symphyomyrtus have radiated in the temperate climate of the south-east of the continent and together contain most of the cool temperate species. The more recently evolved species within the Monocalyptus lineage occur in the southeast and south-west of the continent (Ladiges 1997), with species in Tasmania and at high altitudes on the mainland being considered the most specialised (Pryor and Johnson 1981). The most primitive species from this lineage occur in north-east Australia (including the subgenera Gaubaea and Idiogenes; Ladiges 1997). The subgenus Symphyomyrtus is the most widespread, with species occurring throughout Australia. Within Symphyomyrtus, the section Adnataria (boxes, iron barks) is widespread, but predominates in the subtropics. Transversaria (eastern blue gums, red mahoganies, grey gums) is mainly an eastern section, with E. diversicolor (karri) the only species in the south-west (Brooker and Kleinig 1990b). The sections Bisectaria (mallees and gums) and Dumaria (mallees) are centred on the south-west and include many species of mallee habit. Bisectaria is the more diverse and includes species of moister forest sites. Its species dominate or codominate eucalypt communities in a large portion of the medium to dry parts of south-west Australia. Younger and more fertile soils have developed on the inland slopes of ranges both in New South Wales/ Victoria and the Darling Range in Western Australia. In the east these soils are occupied by species from the section Adnataria, but in the west they are occupied by species mainly from Bisectaria and to some extent Dumaria (Pryor and Johnson 1981). The section Exsertaria (northern red gums, eastern red gums) includes mainly tropical and eastern species and, except for E. rudis, is absent from south-west Australia.

19

D I S E A S E S

A N D

P A T H O G E N S

O F

E U C A L Y P T S

The subgenus Eudesmia is a small but diverse group of 20 species, several of which are widespread (Pryor and Johnson 1981). The eudesmid species are mostly tropical, or occur in drier regions of the south-west and across the interior of northern Australia, but are absent from non-tropical regions of the east. Corymbia (bloodwoods) are also relatively diverse and widespread. Tropical and subtropical species predominate, but several red bloodwood species (section Rufaria) extend into the winter rainfall areas of south-west (C. ficifolia, C. calophylla) and southeast (C. maculata) Australia. Within Corymbia, there is a trend for more primitive groups to occur in regions of relatively humid climate and groups with more recently evolved characteristics to occur in more drought-prone regions (Hill and Johnson 1995). At the higher taxonomic level, diversity is greatest in the north-east of the continent, where five subgenera of Eucalyptus s. str. occur along with Corymbia and Angophora (Ladiges 1997). Diversity is low in the south-west where only three subgenera and Corymbia occur, and on the island of Tasmania where only one section of both Symphyomyrtus and Monocalyptus are represented (Williams and Potts 1996; Wardell-Johnson et al. 1997). On a continental scale, eucalypt species richness is greatest in a broad band along the temperate, subcoastal regions of south-east Australia, with secondary concentrations of species in the semiarid south-west and west, and tropical north and north-east regions (Gill et al. 1985; Wardell-Johnson et al. 1997). The transitional rainfall zone of south-west Australia may also prove to be one of the more diverse areas. Species richness is highest in the open forests of south-east Australia, where up to 10 different species may occur per hectare, as species often grow in mixtures and species replacement across the landscape is high (Wardell-Johnson et al. 1997). Within this region, species richness increases on warmer, drier sites (Margules et al. 1987). In natural forests, species frequently occur in a mosaic distribution with their boundaries following a similar mosaic of often fine-scale, environmental variation (e.g. Hogg and Kirkpatrick 1974; Ashton 1976; Kirkpatrick 1981; Austin et al. 1983a; Davidson 1987; Specht 1996). Replacement series often occur along environmental gradients (e.g. altitude, drought) with relatively sharp boundaries delimiting species (Ashton 1981a). Some natural eucalypt forests are dominated

20

by a single species, as with E. regnans in the south-east and E. diversicolor in the south-west (Ashton 1981b). However, eucalypts mostly occur in mixtures of two or more species. Species may co-occur in intermediate, transitional environments (Ashton 1981a) or where fine-scale environmental patchiness occurs (e.g. Battaglia and Williams 1996). In south-east Australia and Tasmania, forests comprising an intimate mix of species from both the Symphyomyrtus and Monocalyptus subgenera are relatively common and species from different subgenera co-occur more frequently than species from the same subgenera (Pryor 1976; Austin et al. 1983b). This trend is believed to be associated with niche displacement because the two subgenera differ in numerous ecological and biological attributes (Noble 1989), including disease susceptibility (see Chapter 9), coupled with complete reproductive isolation between, but not within, the two subgenera (Griffin et al. 1988). An important feature of eucalypt distribution patterns is that many of the recognised taxa intergrade, resulting in species complexes where no clear morphological discontinuity is apparent (Pryor and Johnson 1971; Pryor 1976). Taxa are often separated along altitudinal, continental or simply geographical, gradients. Classic examples of such clinal variation with altitude include the E. pauciflora–niphophila complex in the mountain ranges of south-east Australia (Pryor 1957; reviewed in Pryor 1976; Potts and Wiltshire 1997) and the transition from the tall forest tree E. johnstonii, through E. subcrenulata, to the alpine shrub, E. vernicosa, which occurs on several Tasmanian mountains (Potts and Jackson 1986). Some species have large geographical ranges; for example E. camaldulensis is distributed over most of Australia except for the south-west (Eldridge et al. 1993). Eucalyptus tereticornis also occurs in an extended north-south distribution from Papua to eastern Victoria (Eldridge et al. 1993). However, there are many species with very restricted distributions (e.g. Crisp 1988; Prober et al. 1990a, 1990b; Wiltshire et al. 1990; Sampson et al. 1995; Kennington and James 1997) and many of these are threatened (Pryor and Briggs 1981). There is ample evidence for major changes in species ranges and extinctions through recent geological time (e.g. Pryor 1976; Potts 1986; Martin and Gadek 1988; Potts 1990). Using changes in pollen proportions, Churchill (1968), for example, detailed

M O RP HO LO GY , P HYL OGENY , O R IGIN , D IST R I BU T I ON

A ND

G ENE TIC D IVE RSITY

OF

E UCA LYPTS

C H A P T E R

2

fluctuations in the ranges of three forest species, C. calophylla, E. diversicolor and E. marginata, in south-west Australia over the last 7000 years which were believed to be due to changing rainfall patterns. About 16% of eucalypt species have major disjunctions of more than 140 kilometres in their range (Chippendale and Wolf 1981). With such poor seed dispersal mechanisms, these disjunctions suggest that extant populations are remnants of former, more widespread distributions (Pryor and Johnson 1971; Parsons 1986). Eucalyptus perriniana, for example, occurs as several small populations in the Australian Alps and in three small populations on the island of Tasmania (Wiltshire and Reid 1987). In this case, genetic differentiation across the disjunction is relatively small, although populations can be differentiated. In some other species occurring both in Tasmania and on the mainland, variation appears to be continuous, as in the case of E. obliqua (Brown et al. 1976) and E. regnans (Griffin et al. 1982). However, the Tasmanian and mainland forms of E. delegatensis have distinct morphological differences which have led to subspecific recognition (Boland and Dunn 1985). About 59% of the Tasmanian eucalypts are endemic and concentrated in the south-east of the island (Williams and Potts 1996). The island would have been linked to the mainland of Australia when Pleistocene glacial sea levels were low. The south-east of the island appears to have been a major area of eucalypt speciation in Tasmania (Ladiges et al. 1983), and the endemic groups and relict distributions of species with mainland affinities suggest periods of isolation and reciprocal invasion (Jackson 1965). Other disjunctions in the southern Australian flora appear to be associated with the major geographical and/or ecological barrier arising from the incursion of the Early Miocene sea into the Eucla and Murray Basins (Parsons 1969; Specht 1996). Indeed, the patterns of species distributions within the various eucalypt lineages is consistent with relictual distributions overlaid with distributions suggesting recent radiation and vicariant (allopatric) speciation events (Prober et al. 1990a; Hill and Johnson 1995).

Johnson 1971; Pryor and Johnson 1981; Griffin et al. 1988; Hill and Johnson 1995). Although the importance of hybridisation in eucalypt evolution has yet to be fully understood, there is little doubt that reticulate (anastomosing) evolution is common at lower taxonomic levels and that both vicariant differentiation and hybridisation (secondary intergradation) have been important in shaping extant variation patterns (Pryor and Johnson 1971; Parsons and Kirkpatrick 1972; Ashton 1981a; Pryor and Johnson 1981; Potts and Jackson 1986; Potts and Reid 1988; Potts 1990; Potts and Wiltshire 1997; Steane et al. 1998). Artificial and natural hybridisation in eucalypts has been reviewed by Pryor and Johnson (1971), Pryor (1976), Griffin et al. (1988) and Potts and Wiltshire (1997). In most cases, morphological and physiological traits are inherited in a more-or-less intermediate manner in first generation (F1) hybrids (Fig. 2.8), although there are exceptions and the exact degree of dominance may vary between traits and species combinations. Hybrids may occur:

2.6 Hybridisation

Griffin et al. (1988) analysed records of hybridisation from herbaria and the literature and found that the extent of natural hybridisation between species varies considerably, depending upon numerous factors, including the degree of spatial, ecological and taxonomic separation between putative parents. Using

Hybridisation between recognised eucalypt taxa is frequently reported and, along with often marked clinal variation within species, contributes to difficulties in species identification (Pryor and

1

along species boundaries, as sporadic individuals

2

in hybrid swarms where hybridisation has extended beyond the first generation

3

in zones of introgression.

Some taxonomically intermediate populations, which are isolated from one or both putative parents, are often considered to be the genetic remnants of a past distribution of one or both putative parental species and are termed ‘phantom hybrids’ (Pryor and Johnson 1971; Parsons and Kirkpatrick 1972). For example, a population that is morphologically intermediate between E. cypellocarpa and E. globulus at Mallacoota, Vic., is believed to be a remnant of the E. globulus distribution in this area (Kirkpatrick et al. 1973). However, in other cases such intermediate populations are believed to result from long-distance dispersal (Ashton and Sandiford 1988; Potts and Reid 1988), or to be the remnants of ancestral lineages or other taxa (Watson et al. 1987, cf. Parsons and Kirkpatrick 1972).

21

D I S E A S E S

Figure 2.8

A N D

P A T H O G E N S

O F

Leaves and capsules of Eucalyptus urnigera (left), E. globulus (right) and their F1 hybrid (centre).

Pryor and Johnson’s (1971) classification, they found that within subgenera the frequency of natural hybrid combinations decreased with increasing taxonomic distance between the two parents (i.e. intersectional < interseries < intraseries). Important exceptions were recorded in the subgenus Monocalyptus and the former subgenus Corymbia where intersectional hybrids were as common as intrasectional hybrids, signalling taxonomic problems (see Ladiges and Brooker 1987; Sale et al. 1993; Hill and Johnson 1995; Ladiges 1997). Across the genus, natural hybridisation was relatively restricted, with only 15% of actual combinations expected on geographical grounds having been recorded. The main subgenera do not hybridise either naturally or artificially (Pryor and Johnson 1971; Griffin et al. 1988; Ellis et al. 1991). However, there are reports of natural intersubgeneric hybrids between the two sister subgenera Idiogenes and Monocalyptus (E. cloeziana × E. acmenoides; Brooker and Kleinig 1994; Hill and Johnson 1995) and between species previously classified in the subgenus Blakella and subgenus Corymbia (Wardell-Johnson et al. 1997). Estimates of the background rate of natural F1 hybridisation in 11 ‘pure’ eucalypt species range from 0.06% to 3.48%

22

E U C A L Y P T S

(mean 1.3%) (Potts and Wiltshire 1997), but this rate may markedly increase in multispecies plantations and ornamental plantings. Differences in flowering time (Drake 1980; Potts and Reid 1985; Williams and Potts 1996), style size (Gore et al. 1990), physiological incongruity (Ellis et al. 1991) and reduced hybrid fitness (Pryor and Johnson 1971; Drake 1981; Potts 1986; Morrow et al. 1994) have all been shown to be important in maintaining species integrity. An important component of reduced hybrid fitness appears to be their increased susceptibility to pests and diseases. Several studies have demonstrated that insect herbivores and fungal pathogens concentrate on natural hybrids (Drake 1981; Whitham et al. 1991; Morrow et al. 1994; Whitham et al. 1994), due to rarity per se (Drake 1981) or increased genetic susceptibility (Dungey et al. 1994) of host trees. The severity of Mycosphaerella leaf blotch in a field trial in north-west Tasmania was higher on juvenile leaves of F1 hybrids between E. nitens and E. globulus than on either pure species, but severity on adult leaves was intermediate between that on the parents (Dungey et al. 1997).

M O RP HO LO GY , P HYL OGENY , O R IGIN , D IST R I BU T I ON

A ND

2.7 Genetic variation The exceptional differentiation observed among eucalypts may be unparalleled for woody plants (Wardell-Johnson et al. 1997). From north to south, the Australian continent changes from summer to winter rainfall and from warm to cooler seasons which, combined with the effect of variations in altitude, aspect and soils, has resulted in an immense diversity of habitats to which eucalypts have adapted (see Eldridge et al. 1993; Specht 1996). Broad ecological trends are evident at higher taxonomic levels (reviewed by Pryor and Johnson 1981; Noble 1989; Specht 1996). Closely related taxa often exhibit marked ecological segregation (e.g. Williams and Potts 1996) and many groups have specialised taxa restricted to unique environments, such as serpentine outcrops (Specht 1996) and saline soils (Wardell-Johnson et al. 1997) over all, or parts, of their range. Within species, marked genetic differentiation between populations is normal rather than the exception (Pryor and Johnson 1971; Pryor 1976; Eldridge et al. 1993; Potts and Wiltshire 1997) and assessment of the performance of a species will often require sampling from throughout its geographical and ecological range (Pederick 1979; Eldridge et al. 1993; Potts and Jordan 1994). Studies of allozyme variation have shown the level of differentiation between populations of eucalypt species to be more than twice that of wind-pollinated conifers and northern hemisphere angiosperm tree species (Moran 1992). Widespread eucalypt species have greater overall and within-population genetic diversity than species with regional and localised distributions, yet population differentiation is greatest in regional species (Moran and Hopper 1987; Moran 1992; Potts and Wiltshire 1997). Variation between populations in quantitative traits is mostly continuous and is often clinal, paralleling environmental gradients associated with changes in, for example, latitude, continentality or altitude (see Pryor 1976; Potts and Jackson 1986; Potts and Wiltshire 1997). Steep environmental gradients may elicit rapid changes in phenotype over short distances, often involving many characters. In E. urnigera, for example, a transition from populations with completely green foliage to populations with completely glaucous foliage occurs over an altitude range of 200 metres on

G ENE TIC D IVE RSITY

OF

E UCA LYPTS

C H A P T E R

2

Mt Wellington, Tas. (Barber and Jackson 1957; Potts and Jackson 1986). When the progeny of trees selected from E. regnans populations at different altitudes on the southern slopes of Mt Erica, Vic., were grown together on a common test site, their growth rate decreased clinally with increasing altitude of origin (Eldridge 1972) and frost resistance, as determined in the laboratory, increased with increasing altitude of the selected parents (Eldridge 1968). Clinal variation may be more gradual where broadscale climatic changes occur over the geographical range of widespread species. Genetic variation in the widespread E. camaldulensis, for example, has been extensively studied from field trials established around the world for breeding purposes (reviewed in Midgley et al. 1989; Eldridge et al. 1993). A northern and southern form of this species has been detected in several studies, although no distinct boundary exists between them. The northern form has rounded or conical opercula, broad glaucous juvenile leaves, relatively straight stems and white bark. In contrast, the southern form has ‘beaked’ opercula, narrow and non-glaucous juvenile leaves, relatively crooked stems, mottled grey bark and rarely produces lignotubers. Longitudinal clines in several traits have also been demonstrated across northern Australia (Grunwald and Karschon 1982) and E. camaldulensis intergrades with E. tereticornis in northern Queensland (Doran and Burgess 1996) and E. rudis in south-west Western Australia (Pryor and Byrne 1969). Marked climatic adaptation is demonstrated by the better performance in tropical countries of northern provenances from summer rainfall areas such as Katherine, NT, and Petford, Qld, whereas a southern provenance from Lake Albacutya, Vic., with winter rainfall, is best in Mediterranean countries. There is also variation in the polyphenolic constituents of leaves (Banks and Hillis 1969). For example, an unusually high concentration of 1,8-cineole occurs in eucalypt oil distilled from certain populations from Queensland (Doran and Brophy 1991). Intraspecific variation in 1,8-cineole is highly heritable in E. camaldulensis (Doran and Matheson 1994) and is associated with resistance to insect herbivory (Stone and Bacon 1994). The extent and pattern of genetic variation in quantitative traits (i.e. the genetic architecture) is usually determined from common environment

23

D I S E A S E S

A N D

P A T H O G E N S

O F

progeny trials based on open-pollinated seed collected from trees growing in native stands (reviewed in Eldridge et al. 1993; Potts and Wiltshire 1997). The heritability of traits can be estimated where family identity is maintained (see Eldridge et al. 1993). The use of open-pollinated progeny is a cheap and expedient means of studying genetic variation in eucalypts. However, in such cases, the male pedigree is unknown and there may be variable levels of inbreeding due to selfing (e.g. Hardner and Potts 1995a; Hardner and Potts 1997) or the crossing of related neighbours (Eldridge et al. 1993; Hardner et al. 1997) and natural outcrossing may not be random. Open-pollinated progenies may thus yield poor estimates of genetic parameters such as narrow-sense heritability and breeding values (Griffin and Cotterill 1988; Hardner and Potts 1995b; Potts et al. 1995b; Borralho and Potts 1996; Hodge et al. 1996). Accurate estimation of genetic parameters requires the use of controlled pollinated progenies (e.g. Hodge et al. 1996), although for some traits reasonably good estimates may be obtained from open-pollinated progenies. For example, Dungey et al. (1997) demonstrated that breeding values for damage by Mycosphaerella leaf blotch estimated from native stand open-pollinated progenies and controlled crosses (factorial) of E. globulus were highly correlated and heritability estimates were comparable. The level of genetic variability within a species determines the potential gain that can be achieved in breeding programs. Breeding programs are now established throughout the world for numerous tropical and temperate eucalypt species (see Eldridge et al. 1993; Potts et al. 1995a; Dieters et al. 1996b). In some species the emphasis is on use of vegetative propagation by cuttings to establish clonal plantations (e.g. E. grandis, van Wyk 1985; Eldridge et al. 1993; E. gunnii, Potts and Potts 1986; hybrids, Campinhos and Ikemori 1989). In species which are more difficult to clone, genetically improved seed is produced in seed orchards (e.g. E. globulus, Eldridge et al. 1993; E. nitens, de Little et al. 1993).

2.8 Genetic variation in susceptibility to disease Management of diseases and breeding for disease resistance requires a detailed understanding of the genetic variation and taxonomic relationships among and within both the eucalypt hosts and the

24

E U C A L Y P T S

pathogens and ultimately of the genetic control of the host-pathogen interaction. There are increasing numbers of examples that demonstrate genetic variation in disease susceptibility of eucalypts at the species level, as well as within species where differences in susceptibility between populations and between trees within populations have been reported (Alfenas et al. 1983; Dianese et al. 1984; Dungey et al. 1997). In some cases the pathogen can infect many eucalypt species, but in other cases its host range may be limited to a few closely related species. For example, Mycosphaerella cryptica (Cooke) Hansf., a cause of leaf necrosis and defoliation, has been recorded on 38 eucalypt species from both the Monocalyptus and Symphyomyrtus subgenera, and infects both juvenile and adult leaves (Park and Keane 1982a, 1982b, 1984; see Chapter 9). In contrast, Mycosphaerella nubilosa (Cooke) Hansf. was found to infect only juvenile foliage of three related species in the subgenus Symphyomyrtus (E. bridgesiana, E. cypellocarpa, E. globulus) (Park and Keane 1982a). The fungus Sporothrix pitereka (J.Walker & Bertus) U.Braun & Crous, which causes a shoot blight and leaf spot on seedlings of C. maculata in nurseries (see Chapters 8 and 9), and is possibly the same fungus causing canker on naturally occurring C. calophylla and cultivated C. ficifolia in Western Australia, also has a relatively narrow host range (Walker and Bertus 1971). Inoculation experiments showed that only species in the genus Corymbia were susceptible, along with the only species of Angophora tested, Angophora costata. The similarity in response to this pathogen was cited by Pryor and Johnson (1971) as support for the taxonomic association of Angophora and Corymbia. The soilborne pathogen, Phytophthora (Ph.) cinnamomi Rands, is able to infect the fine roots of most eucalypt species, although the disease develops particularly in species of the subgenus Monocalyptus (Podger and Batini 1971; Marks 1979; Marks and Smith 1991; see Chapter 11). Important forest species within Monocalyptus, E. marginata and E. sieberi, are highly susceptible and are associated with severe disease outbreaks in south-west and south-east Australia, respectively. Generally, species of the other main subgenus, Symphyomyrtus and the genus Corymbia, are resistant. A further example illustrates interspecific and intraspecific variation in resistance of eucalypts to a

M O RP HO LO GY , P HYL OGENY , O R IGIN , D IST R I BU T I ON

A ND

pathogen where both are exotics. The stem canker pathogen, Cryphonectria cubensis (Bruner) Hodges, has caused losses in eucalypt plantations in central and northern coastal regions of Brazil and in Cuba, Surinam and Hawaii, on sites with high temperature and humidity throughout the year (see Chapter 10) (Hodges and Reis 1976). Cryphonectria cubensis has been identified as conspecific with Endothia eugeniae (Nutman & F.M.Roberts) J.Reid & C.Booth, a weak pathogen of the myrtaceous species, clove [Syzygium aromaticum (L.) Merr. & L.M.Perry], which is native to the Moluccas area of Indonesia (Hodges et al. 1986). When clove plants were transported to Brazil and other countries to establish commercial plantations, it appears that the pathogen was distributed with its host and has been able to infect susceptible eucalypts when they have been introduced to the same area. Cryphonectria cubensis appears to have a fairly limited host range, with the most susceptible eucalypts being C. maculata and E. saligna (Hodges et al. 1986). Eucalyptus grandis is moderately susceptible but shows intraspecific variation in resistance. This eucalypt species is widely planted as an exotic in the subtropics. In the large plantations on coastal sites in Brazil, freedom from cankers caused by Cryphonectria cubensis is an important selection criterion for breeding and deployment of eucalypts by the Aracruz company (Campinhos and Ikemori 1989). The plantations, managed on a seven-year rotation, have been reported to be now 100% resistant. This has been achieved by the selection of resistant clones which are vegetatively propagated as cuttings. Some of the clones used in the plantation are hybrids between E. urophylla and E. grandis (Campinhos and Ikemori 1989). Eucalyptus urophylla is very resistant to Cryphonectria cubensis and the hybrids have more resistance than E. grandis. Another aspect of the breeding program at Aracruz is based on the finding that selections from the northern-most natural stands of E. grandis in Australia, on the Atherton Tableland in Queensland, are resistant to the disease when grown in Brazil (even though the disease is not known to occur in Australia). Accordingly, collections of seeds of E. grandis in the Atherton district have been grown at Aracruz to provide an additional genetic resource for the breeding program (Campinhos and Ikemori 1989). Intraspecific variation in the disease resistance of eucalypts has been reported for other diseases.

G ENE TIC D IVE RSITY

OF

E UCA LYPTS

C H A P T E R

2

Several of the 36 provenances of E. regnans in a large trial in New Zealand were severely damaged by M. cryptica, causing heavy defoliation and leader dieback of the young trees (Wilcox 1982). The most susceptible provenance was one that was also the least frost hardy. The author commented that badly frosted trees sometimes resprouted from the base and thus may have been additionally susceptible because of the high proportion of juvenile foliage in the crown. Another of the more susceptible provenances originated from a site north of the Great Dividing Range in Victoria (Rubicon) near stands of E. delegatensis. Wilcox (1982) speculated that the poor disease resistance of this provenance may have been due to some degree of hybridisation with the highly susceptible E. delegatensis, although there was no supportive morphological evidence. Occasional putative hybrids of E. regnans × E. delegatensis that occurred in one of the other provenances were more heavily diseased than pure E. regnans individuals. Provenance variation in the severity of Mycosphaerella leaf blotch has also been reported in field trials of E. globulus (Carnegie et al. 1994; Dungey et al. 1997), E. nitens (Purnell and Lundquist 1986) and E. delegatensis (Dick and Gadgil 1983). In E. globulus, there is evidence that some of the provenance variation results from natural selection favouring genes that confer resistance in disease-prone areas. Outbreaks of Mycosphaerella leaf blotch are favoured by warm, wet weather (Park 1988a, 1988b; Carnegie et al. 1994) and provenances of E. globulus originating from higher summer rainfall areas have greater resistance to the disease than provenances from drier or cooler areas (Carnegie et al. 1994; Dungey et al. 1997). Within populations of E. globulus, the severity of Mycosphaerella leaf blotch in field trials has a low to moderate level of genetic control, with individual narrow-sense heritabilities ranging from 0.1 to 0.3 (Dungey et al. 1997). In a study of controlled crosses, Dungey et al. (1997) showed that heritabilities were consistently higher for disease in adult foliage than juvenile foliage and the variation due to dominance genetic effects was less than half that due to additive genetic effects. Such field assessments may provide reasonably good ranking of families or parental breeding values for breeding purposes as these are based on the average response of progeny, randomly distributed throughout the

25

D I S E A S E S

A N D

P A T H O G E N S

O F

trial. However, studies of natural infection pose problems, firstly, for predicting resistance at the individual level and, secondly, for accurately studying the genetic basis of resistance. Infection levels may not be uniform and susceptible individuals may escape infection. The expression of genetic variation in disease resistance, and hence heritability estimates, may also depend on the overall level of infection (Dieters et al. 1996a; Dungey et al. 1997). Further, in the above examples, damage to the juvenile foliage of E. globulus is due to the combined effects of two pathogens, M. cryptica and M. nubilosa, which usually co-occur on juvenile foliage in south-east Australia and are difficult to distinguish in the field (Carnegie et al. 1994; Dungey et al. 1997; see Chapter 9). The presence of both pathogens may mask a close genetic association between host and pathogen and could explain the generally lower heritabilities and higher levels of damage recorded on juvenile than on adult foliage, in which damage is due only to M. cryptica, recorded in E. globulus by Dungey et al. (1997). Inoculation experiments clearly are required to partition the response to either pathogen. Nevertheless, positive genetic correlations do occur in disease severity between adult and juvenile foliage (Dungey et al. 1997) and seasons (Carnegie et al. 1994), suggesting that similar selections would be made against the different pathogens. Increased disease severity on the juvenile canopy of E. globulus in field trials was found to be genetically correlated with delayed transition from juvenile to adult foliage (rg = 0.54, Dungey et al. 1997). This probably resulted from greater opportunity for disease increase within the larger and longer-lived juvenile canopy. Selection for early transition to adult foliage may thus be one means of reducing damage from Mycosphaerella leaf blotch (Dungey et al. 1997). In Australia, most work has focused on selection and breeding for resistance to Ph. cinnamomi, and this eucalypt–pathogen interaction has been studied more than any other (e.g. Marks 1979; McComb et al. 1987; McComb et al. 1991; Cahill et al. 1992; Cahill and McComb 1992; Cahill et al. 1993; McComb et al. 1994; Stukely and Crane 1994; Bunny et al. 1995; Irwin et al. 1995; see Chapter 11). Genetic variation in susceptibility to Ph. cinnamomi has been reported within many eucalypt species. For example, significantly different rates of disease development occurred in young trees from different families in a

26

E U C A L Y P T S

seedling seed orchard of E. regnans (Harris et al. 1983) and trunk inoculations of trees of similar age and size showed lesions that varied greatly in size from tree to tree depending upon tree genotype (Marks et al. 1981). Such genetic variation is the basis for breeding for disease resistance. There are large differences in the physiological, biochemical and anatomical responses of resistant and susceptible genotypes. Mechanisms of resistance have been best studied in jarrah, E. marginata (McComb et al. 1991; Cahill and McComb 1992; Cahill et al. 1993), in which resistance is under strong genetic control (Stukely and Crane 1994). There is also considerable genetic variation within the pathogen itself (see Irwin et al. 1995) and different isolates have been shown to differ significantly in their pathogenicity against clones of E. marginata and seedlings of several monocalypt species (E. globoidea, E. muelleriana, E. obliqua, E. regnans) (Dudzinski et al. 1993). Significant clone by isolate and species by isolate interactions were detected. In the case of E. marginata, it was only the more pathogenic isolates that allowed resistant and susceptible clones to be distinguished. Different isolates appear to exhibit a differential response to eucalypt host genotypes, but the extent to which gene-for-gene interactions (Keen 1982; Wolfe and McDermott 1994) occur are presently unknown. Nevertheless, Irwin et al. (1995) note that where resistance to Ph. cinnamomi has been detected in native plant species, it is a general or partial resistance.

2.9 Factors affecting disease risk in plantations The risk of disease in plantations is usually considered to be greater than that in natural forests because: 1

there may be less genetic variation present in planted stands

2

site conditions may not suit the requirements of the species, with the result that the trees may grow under stress for all or part of the year.

The main cause of reduced genetic variation in plantations is the use of seed from a limited number of parents or the planting of a limited number of clones. The risk of major losses through disease becomes greater as the genetic base of a plantation is reduced. However, tree breeding does not necessarily reduce genetic variability in deployed populations,

M O RP HO LO GY , P HYL OGENY , O R IGIN , D IST R I BU T I ON

A ND

although a change in the frequency of some genes as a response to selection for desired traits is expected. Most tree breeding programs, involving the production of seed in seed orchards, are designed to maintain genetic variability, partially at the expense of higher gains in economically important characters. A seed orchard with trees derived from several natural populations could produce seed with more genetic variability than would be present in collections from any one natural population, where there may be a degree of inbreeding and limited genetic variation (e.g. Chaisurisri and El-Kassaby 1994). This will provide stability of the crop in the face of risks over long rotations. Nevertheless, growers attracted to the higher yields obtainable from clonal plantations need to be aware of the higher risks of disease due to genetic uniformity. The use of multiclonal plantings has been recommended, particularly if rotations are long (Libby and Ahuja 1993). Indeed, the deployment of a limited number of clones in plantations should be backed by a large, variable breeding population from which alternative clones can be selected to combat various stresses that may occur unexpectedly, including attack by pests and diseases. The environment is also important in determining whether infection is likely to occur. In natural forests an equilibrium is thought to exist between the pathogen, the host species (genotype) and site (environment—both biotic and abiotic), such that disease normally is restricted to fairly low levels, otherwise the host species would be unable to occupy the site. Indeed, disease could be a factor in eliminating species from many potentially suitable sites. Eucalypt plantations, however, have often been planted on sites which differ in some important features, edaphic and/or climatic, from those of the natural distribution of the species involved. As a result, the trees may be growing under stress and are likely to be more susceptible to disease caused by non-specialised pathogens (see Chapter 9). When grown as exotics they may also be exposed to pathogens not present in their natural distribution, as illustrated by Cryphonectria cubensis and the eucalypt rust, Puccinia psidii G.Winter, in Brazil. Plantation managers need to be alert to the many risks. However, there is clear evidence of genetic variation in resistance within eucalypt species with which to combat disease. Selection of well-adapted resistant provenances of a eucalypt species from local

G ENE TIC D IVE RSITY

OF

E UCA LYPTS

C H A P T E R

2

trials, followed by collection of seeds from the best and healthiest trees in each generation, would be a simple method of developing lines with improved resistance. Many tree improvement programs concentrate on selection for growth rate and form, and assume that in doing so a degree of pest and disease resistance is also selected. More rapid progress to resistance could be obtained from designed breeding programs specifically targeting resistance to diseases as a breeding objective for particular breeding populations. Molecular technology is now being used to find DNA markers associated with quantitative trait loci (QTL) that control disease resistance. This will potentially allow selection for disease resistance in the absence of epidemics and without recourse to complex bioassays (e.g. Young 1996). Nevertheless, the interactions between genotypes of the eucalypt and pathogen, and environmental factors are likely to be complex and understanding these interactions is the challenge for future research and breeding.

2.10 Acknowledgments We thank Dr René Vaillancourt and Dr Greg Jordan for their valued comments on the manuscript.

2.11 References Alfenas, A.C., Jeng, R. and Hubbes, M. (1983). Virulence of Cryphonectria cubensis on Eucalyptus species differing in resistance. European Journal of Forest Pathology 13, 197–205. Ashton, D.H. (1976). The vegetation of Mount Piper, Central Victoria: A study of a continuum. Journal of Ecology 64, 463–483. Ashton, D.H. (1981a). The ecology of the boundary between Eucalyptus regnans F. Muell. and E. obliqua L’Herit. in Victoria. Proceedings of the Ecological Society of Australia 11, 75–94. Ashton, D.H. (1981b). Tall open-forests. In Australian Vegetation. (Ed. R.H. Groves) pp. 121–151. (Cambridge University Press: Cambridge.) Ashton, D.H. and Sandiford, L.M. (1988). Natural hybridisation between Eucalyptus regnans F. Muell. and E. macrorhyncha F. Muell. in the Cathedral Range, Victoria. Australian Journal of Botany 36, 1–22. Austin, M.P., Cunningham, R.B. and Good, R.B. (1983a). Altitudinal distribution of several eucalypt species in relation to other environmental factors in southern New South Wales. Australian Journal of Ecology 8, 169–180. Austin, M.P., Cunningham, R.B. and Wood, J.T. (1983b). The subgeneric composition of eucalypt forest stands

27

D I S E A S E S

A N D

P A T H O G E N S

O F

in a region of south-eastern Australia. Australian Journal of Botany 31, 63–71. Banks, J.C.G. and Hillis, W.E. (1969). The characterization of populations of Eucalyptus camaldulensis by chemical features. Australian Journal of Botany 17, 133–146. Barber, H.N. and Jackson, W.D. (1957). Natural selection in action in Eucalyptus. Nature 179, 1267–1269. Barlow, B.A. (1981). The Australasian flora: its origin and evolution. In Flora of Australia. (Eds R. Robertson, B.G. Briggs, H. Eichler, L. Pedley, J.H. Ross, D.F. Symon and P.G. Wilson) pp. 25–75. (Australian Government Publishing Service: Canberra.) Battaglia, M. and Reid, J.B. (1993). Ontogenetic variation in frost resistance of Eucalyptus delegatensis RT Baker. Australian Journal of Botany 41, 137–141. Battaglia, M. and Williams, K. (1996). Mixed species stands of eucalypts as ecotones on a water supply gradient. Oecologia 108, 518–528. Boland, D.J., Brooker, M.I.H., Chippendale, G.M., Hall, N., Hyland, B.P.M., Johnston, R.D., Kleinig, D.A. and Turner, J.D. (1985). Forest Trees of Australia. (Australian Government Publishing Service: Melbourne.) Boland, D.J. and Dunn, A.T. (1985). Geographic variation in Alpine Ash (Eucalyptus delegatensis R.T. Baker). Australian Forest Research 15, 155–171. Boland, D.J., Brooker, M.I.H., Turnbull, J.W. and Kleinig, D.A. (1980). Eucalyptus Seed. (CSIRO: Melbourne.) Borralho, N.M.G. and Potts, B.M. (1996). Accounting for native stand characteristics in genetic evaluations of open pollinated progeny from Eucalyptus globulus base population. New Forests 11, 53–64. Brooker, M.I.H. (1986). An introduction to the study of characters in Eucalyptus. In Proceedings of a Workshop on Seed Handling and Eucalypt Taxonomy. pp. 119–142. (Eds R.D. Ayling and B.R.T. Seward) (International Development Research Centre: Ottawa.) Brooker, M.I.H. and Hopper, S.D. (1991). A taxonomic revision of Eucalyptus wandoo, E. redunca, and allied species (Eucalyptus series Leucispermae MaidenMyrtaceae) in Western Australia. Nuytsia 8, 1–189. Brooker, M.I.H. and Kleinig, D.A. (1990a). Field Guide to Eucalypts. Volume 1. South-eastern Australia. (Inkata Press: Melbourne.) Brooker, M.I.H. and Kleinig, D.A. (1990b). Field Guide to Eucalypts. Volume 2. South-western and Southern Australia. (Inkata Press: Sydney.) Brooker, M.I.H. and Kleinig, D.A. (1994). Field Guide to Eucalypts. Volume 3. Northern Australia. (Inkata Press: Sydney.) Brown, A.G., Eldridge, K.G., Green, J.W. and Matheson, A.C. (1976). Genetic variation of Eucalyptus obliqua in field trials. New Phytologist 77, 193–203. Bunny, F.J., Crombie, D.S. and Williams, M.R. (1995). Growth of lesions of Phytophthora cinnamomi in

28

E U C A L Y P T S

stems and roots of jarrah (Eucalyptus marginata) in relation to rainfall and stand density in mediterranean forest of Western Australia. Canadian Journal of Forest Research 25, 961–969. Cahill, D.M. and McComb, J.A. (1992). A comparison of changes in phenylalanine ammonialyase activity, lignin and phenolic synthesis in the roots of Eucalyptus calophylla (field resistant) and E. marginata (susceptible) when infected with Phytophthora cinnamomi. Physiological and Molecular Plant Pathology 40, 315–332. Cahill, D.M., Bennett, I.J. and McComb, J.A. (1992). Resistance of micropropagated Eucalyptus marginata to Phytophthora cinnamomi. Plant Disease 76, 630–632. Cahill, D.M., Bennett, I.J. and McComb, J.A. (1993). Mechanisms of resistance to Phytophthora cinnamomi in clonal, micropropagated Eucalyptus marginata. Plant Pathology 42, 865–872. Cameron, R.J. (1970). Light intensity and the growth of Eucalyptus seedlings I. Ontogenetic variation in E. fastigata. Australian Journal of Botany 18, 29–43. Campinhos, E. and Ikemori, Y.K. (1989). Selection and management of the basic population Eucalyptus grandis and E. urophylla established at Aracruz for the long term breeding programme. In Breeding Tropical Trees: Population Structure and Genetic Improvement Strategies in Clonal and Seedling Forestry. Proceedings of the IUFRO Conference, Pattaya, Thailand, November 1988. (Eds G.L. Gibson, A.R. Griffin and A.C. Matheson) pp. 169–175. (Oxford Forestry Institute; Winrock International: Oxford, UK; Arlington, USA.) Carnegie, A.J., Keane, P.J., Ades, P.K. and Smith, I.W. (1994). Variation in susceptibility of Eucalyptus globulus provenances to Mycosphaerella leaf disease. Canadian Journal of Forest Research 24, 1751–1757. Carr, S.G.M. (1973). Problems of the geography of the tropical eucalypts. In Bridge and Barrier: The Natural and Cultural History of Torres Strait. (Ed. D. Walker) pp. 153–182. (Australian National University: Canberra.) Chaisurisri, K. and El-Kassaby, Y.A. (1994). Genetic diversity in a seed production population vs natural populations of Sitka spruce. Biodiversity and Conservation 3, 512–523. Chappill, J.A. and Ladiges, P.Y. (1996). Phylogenetic analysis of Eucalyptus Informal Subgenus Symphyomyrtus Section Maidenaria. Australian Systematic Botany 9, 71–93. Chippendale, G.M. (1988). Eucalyptus, Angophora (Myrtaceae). Flora of Australia. Vol. 19 (Australian Government Publishing Service: Canberra.) Chippendale, G.M. and Wolf, L. (1981). The Natural Distribution of Eucalyptus in Australia. Special Publication No. 6 (Australian National Parks and Wildlife Service: Canberra.)

M O RP HO LO GY , P HYL OGENY , O R IGIN , D IST R I BU T I ON

A ND

Churchill, D.M. (1968). The distribution and prehistory of Eucalyptus diversicolor F. Muell., E. marginata Donn ex Sm., and E. calophylla R.Br. in relation to rainfall. Australian Journal of Botany 16, 125–151. Crisp, M.D. (1988). Eucalyptus recurva (Myrtaceae), a new species from the Southern Tablelands of New South Wales. Telopea 3, 223–230. Davidson, N.J. (1987). Ecophysiological studies of factors determining the distribution of subalpine eucalypts at Snug Plains, southern Tasmania. Australian Journal of Ecology 12, 197–199. de Little, D.W., Tibbits, W.N., Rasmussen, G.F. and Ravenwood, I.C. (Eds) (1993). Genetic improvement strategy for APPM eucalypt tree farms in Tasmania. Mass production technology for genetically improved fast growing forest tree species. Proceedings of the AFOCEL/IUFRO Conference, Bordeaux, France, 14–18 September 1992 (Association Fôret-Cellulose: Nangis, France.) Dettmann, M.E. (1994). Structure and floristics of Cretaceous vegetation of southern Gondwana: implications for angiosperm biogeography. Palaeobotanist 41, 224–233. Dianese, J.C., Moraes, T.S. de A. and Silva, A.R. (1984). Response of Eucalyptus to field infection by Puccinia psidii. Plant Disease 68, 314–316. Dick, M. and Gadgil, P.D. (1983). Eucalyptus Leaf Spots. Forest Pathology in New Zealand 1. New Zealand Forest Service, Forest Research Institute, Rotorua, New Zealand. Dieters, M.J., Hodge, G.R. and White, T.L. (1996a). Genetic parameter estimates for resistance to rust (Cronartium quercuum) infection from full-sib tests of slash pine (Pinus elliottii), modelled as functions of rust incidence. Silvae Genetica 45, 235–242. Dieters, M.J., Matheson, A.C., Nikles, D.G., Harwood, C.E. and Walker, S.M.e. (Eds) (1996b). Tree Improvement for Sustainable Tropical Forestry. Proceedings of the QFRI–IUFRO Conference, Caloundra, Queensland, Australia, 27 October– 1 November 1996. (Queensland Forestry Research Institute: Gympie.) Doran, J.C. and Brophy, J.J. (1991). Tropical red gums— source of 1,8-cineole-rich Eucalyptus oil. New Forests 4, 157–178. Doran, J.C. and Burgess, I.P. (1996). Variation in floral bud morphology in the intergrading zones of Eucalyptus camaldulensis and E. tereticornis in northern Queensland. Commonwealth Forestry Review 72, 198–202. Doran, J.C. and Matheson, A.C. (1994). Genetic parameters and expected gains from selection for monoterpene yields in Petford Eucalyptus camaldulensis. New Forests 8, 155–167. Drake, D.W. (1980). Contrasting success of natural hybridization in two Eucalyptus species pairs. Australian Journal of Botany 28, 167–191.

G ENE TIC D IVE RSITY

OF

E UCA LYPTS

C H A P T E R

2

Drake, D.W. (1981). Reproductive success of two Eucalyptus hybrid populations. II Comparison of predispersal seed parameters. Australian Journal of Botany 29, 37–48. Drinnan, A.M. and Ladiges, P.Y. (1989). Operculum development in Eucalyptus cloeziana and Eucalyptus informal subg. Monocalyptus (Myrtaceae). Plant Systematics and Evolution 166, 183–196. Dudzinski, M.J., Old, K.M. and Gibbs, R.J. (1993). Pathogenic variability in Australian isolates of Phytophthora cinnamomi. Australian Journal of Botany 41, 721–732. Dungey, H.S., Potts, B.M., Whitham, T.G. and Morrow, P.A. (1994). Plant hybrid zones as centres of biodiversity: evidence from Eucalyptus. In Conserving Biological Diversity in Temperate Forest Ecosystems—Towards Sustainable Management. pp. 67–68. (Centre for Resource and Environmental Studies, ANU: Canberra.) Dungey, H.S., Potts, B.M., Carnegie, A.J. and Ades, P.K. (1997). Mycosphaerella leaf disease: Genetic variation in damage to Eucalyptus nitens, E. globulus and their F1 hybrid. Canadian Journal of Forest Research 27, 750–759. Eldridge, K.G. (1968). Physiological studies of altitudinal variation in Eucalyptus regnans. Proceedings of the Ecological Society of Australia 3, 70–76. Eldridge, K.G. (1972). Genetic variation in the growth of Eucalyptus regnans from an altitudinal transect of Mount Erica, Victoria. (Forestry and Timber Bureau: Canberra.) Eldridge, K., Davidson, J., Harwood, C. and van Wyk, G. (1993). Eucalypt Domestication and Breeding. (Clarendon Press: Oxford.) Ellis, M.F. and Sedgley, M. (1993). Gynodioecy and male sterility in Eucalyptus leucoxylon F. Muell. (Myrtaceae). International Journal of Plant Sciences 154, 314–324. Ellis, M.F., Sedgley, M. and Gardner, J.A. (1991). Interspecific pollen–pistil interaction in Eucalyptus L’Hér. (Myrtaceae); the effect of taxonomic distance. Annals of Botany 68, 185–194. Farrow, R.A., Floyd, R.B. and Neumann, F.G. (1994). Inter-provenance variation in resistance of Eucalyptus globulus juvenile foliage to insect feeding. Australian Forestry 57, 65–68. Florence, R.G. (1981). The biology of the eucalypt forest. In The Biology of Australian Plants. (Eds J.S. Pate and A.J. McComb) pp. 147–180. (University of Western Australia Press: Nedlands.) Frenguelli, J. (1953). Restos del genero Eucalyptus en el Mioceno de Neuquen. Notas Museo Planta 16, 209–213. Gill, A.M., Belbin, L. and Chippendale, G.M. (1985). Phytogeography of Eucalyptus in Australia. Australian Flora and Fauna Series Number 3. (Australian Government Publishing Service: Canberra.)

29

D I S E A S E S

A N D

P A T H O G E N S

O F

Gore, P.L., Potts, B.M., Volker, P.W. and Megalos, J. (1990). Unilateral cross-incompatibility in Eucalyptus : the case of hybridisation between E. globulus and E. nitens. Australian Journal of Botany 38, 383–394. Griffin, A.R. and Cotterill, P.P. (1988). Genetic variation in growth of outcrossed, selfed and open-pollinated progenies of Eucalyptus regnans and some implications for breeding strategy. Silvae Genetica 37, 124–131. Griffin, A.R., Burgess, I.P. and Wolf, L. (1988). Patterns of natural and manipulated hybridisation in the genus Eucalyptus L’Herit.—a review. Australian Journal of Botany 36, 41–66. Griffin, A.R., Williams, E.R. and Johnson, K.W. (1982). Early height growth and frost hardiness of Eucalyptus regnans provenances in twelve field trials in south-east Australia. Australian Forest Research 12, 263–279. Grunwald, C. and Karschon, R. (1982). Leaf xylem water potentials and water saturation deficits as related to seed origin of Eucalyptus camaldulensis Dehn. Australian Forest Research 12, 165–173. Hardner, C.M. and Potts, B.M. (1995a). Inbreeding depression and changes in variation after selfing Eucalyptus globulus subsp. globulus. Silvae Genetica 44, 46–54. Hardner, C.M. and Potts, B.M. (1995b). The influence of mortality and stand age on the estimation of genetic parameters in Eucalyptus regnans. In Eucalypt Plantations: Improving Fibre Yield and Quality. Proceedings of the CRCTHF–IUFRO Conference, Hobart, 19–24 February 1995. (Eds B.M. Potts, N.M.G. Borralho, J.B. Reid, R.N. Cromer, W.N. Tibbits and C.A. Raymond) pp. 208–211. (Cooperative Research Centre for Temperate Hardwood Forestry: Hobart.) Hardner, C.M. and Potts, B.M. (1997). Post-dispersal selection under mixed-mating in Eucalyptus regnans. Evolution 51, 103–111. Hardner, C.M., Potts, B.M. and Gore, P.L. (1997). The relationship between cross success and spatial proximity of Eucalyptus globulus ssp. globulus parents. Evolution 52, 614–618. Harris, J.A., Kassaby, F.Y., Smith, I.W. and Marks, G.C. (1983). Intra-specific variation in resistance to Phytophthora cinnamomi in Eucalyptus regnans. Australasian Plant Pathology 12, 20–22. Hill, K.D. and Johnson, L.A.S. (1995). Systematic studies in the eucalypts 7. A revision of the bloodwoods, genus Corymbia (Myrtaceae). Telopea 6, 185–504. Hill, R.S. (1994). The history of selected Australian taxa. In History of the Australian vegetation: Cretaceous to Recent. (Ed. R.S. Hill) pp. 390–419. (Cambridge University Press: Cambridge.) Hill, R.S. and Carpenter, R.J. (1990). Extensive past distributions for major Gondwanic floral elements: macrosfossil evidence. In Aspects of the Tasmanian Botany—a Tribute to Winifred Curtis. (Eds M.R.

30

E U C A L Y P T S

Banks, S.J. Smith, A.E. Orchard and G. Kantvilas) (Royal Society of Tasmania: Hobart.) Hodge, G.R., Volker, P.W., Potts, B.M. and Owen, J.V. (1996). A comparison of genetic information from open-pollinated and control-pollinated progeny tests in two eucalypt species. Theoretical and Applied Genetics 92, 53–63. Hodges, C.S. and Reis, M.S. (1976). A canker disease of Eucalyptus in Brazil caused by Diaporthe cubensis. Brazilian Institute for Forestry Development, United Nations Development Programme and Food and Agriculture Organisation of the United Nations, DP/ BRA/71/545 Field Document No 14. (Food and Agriculture Organization of the United Nations: Rome.) Hodges, C.S., Alfenas, A.C. and Ferreira, F.A. (1986). The conspecificity of Cryphonectria cubensis and Endothia eugeniae. Mycologia 78, 343–350. Hogg, A. and Kirkpatrick, J.B. (1974). The phytosociology and synecology of some Tasmanian eucalypt forests and woodlands. Journal of Biogeography 1, 227–245. Holmes, W.B.K., Holmes, F.M. and Martin, H.A. (1983). Fossil Eucalyptus remains from the middle Miocene chalk mountain formation, Warrumbungle Mountains, New South Wales. Proceedings of the Linnean Society of New South Wales 106, 299–310. House, A.P.N. and Bell, J.C. (1994). Isozyme variation and mating system in Eucalyptus urophylla S. T. Blake. Silvae Genetica 43, 167–176. House, S.M. (1997). Reproductive biology of eucalypts. In Eucalypt Ecology: Individuals to Ecosystems. (Eds J. Williams and J. Woinarski) pp. 30–55. (Cambridge University Press: Cambridge.) Irwin, J.A.G., Cahill, D.M. and Drenth, A. (1995). Phytophthora in Australia. Australian Journal of Agricultural Research 46, 1311–1337. Jackson, W.D. (1965). The Vegetation. In Atlas of Tasmania. (Ed. J.L. Davies) pp. 30–35. (Government Printer: Hobart.) Jackson, W.D. (1968). Fire, air, water and earth—an elemental ecology of Tasmania. Proceedings of the Ecological Society of Australia 3, 9–16. Jacobs, M.R. (1955). Growth Habits of the Eucalypts. (Commonwealth of Australia Forestry and Timber Bureau: Canberra.) Johnson, L.A.S. (1972). Evolution and classification in Eucalyptus. Proceedings of the Linnean Society of New South Wales 97, 11–29. Johnson, L.A.S. (1976). Problems of species and genera in Eucalyptus (Myrtaceae). Plant Systematics and Evolution 125, 155–167. Johnson, L.A.S. and Briggs, B.G. (1981). Three old southern families—Mytraceae, Proteaceae and Restionaceae. In Ecological Biogeography of Australia. (Ed. A. Keast) pp. 427–469. (W. Junk: The Hague.)

M O RP HO LO GY , P HYL OGENY , O R IGIN , D IST R I BU T I ON

A ND

Johnson, L.A.S. and Briggs, B.G. (1984). Myrtales and Myrtaceae—a phylogenetic analysis. Annals of the Missouri Botanical Gardens 71, 700–756. Keen, N.T. (1982). Specific recognition in gene-for-gene host parasite systems. Advances in Plant Pathology 1, 35–82. Kennington, W.J. and James, S.H. (1997). Contrasting patterns of clonality in two closely related mallee species from Western Australia, Eucalyptus argutifolia and E. obtusiflora (Myrtaceae). Australian Journal of Botany 45, 679–689. Kershaw, A.P. (1986). Climatic change and aboriginal burning in north-east Australia during the last two glacial interglacial cycles. Nature 322, 47–49. Kershaw, A.P., Martin, H.A. and McEwen Mason, J.R.C. (1994). The Neogene: a period of transition. In History of the Australian vegetation: Cretaceous to Recent. (Ed. R.S. Hill) pp. 299–327. (Cambridge University Press: Cambridge.) Kirkpatrick, J.B. (1981). A transect study of forests and woodlands on dolerite in the Eastern Tiers, Tasmania. Vegetatio 44, 155–163. Kirkpatrick, J.B., Simmons, D. and Parsons, R.F. (1973). The relationship of some populations involving Eucalyptus cypellocarpa and E. globulus to the problem of phantom hybrids. New Phytologist 72, 867–876. Lacey, C.J. (1974). Rhizomes in tropical eucalypts and their role in recovery from fire damage. Australian Journal of Botany 22, 29–38. Lacey, C.J. and Johnston, R.D. (1990). Woody clumps and clumpwoods. Australian Journal of Botany 38, 299–334. Ladiges, P.Y. (1997). Phylogenetic history and classification of eucalypts. In Eucalypt Ecology: Individuals to Ecosystems. (Eds J. Williams and J. Woinarski) pp. 16–29. (Cambridge University Press: Cambridge.) Ladiges, P.Y. and Brooker, M.I.H. (1987). Cladistic and biogeographic analysis of Western Australian species of Eucalyptus L’Herit., informal subgenus Monocalyptus Pryor & Johnson. Australian Journal of Botany 35, 251–281. Ladiges, P.Y. and Humphries, C.J. (1986). Relationships in the stringybarks, Eucalyptus L’Herit. informal subgenus Monocalyptus series Capitellatae and Olsenianae: phylogenetic hypotheses, biogeography and classification. Australian Journal of Botany 34, 603–632. Ladiges, P.Y., Humphries, C.J. and Brooker, M.I.H. (1983). Cladistic relationships and biogeographical patterns in the peppermint group of Eucalyptus (informal subseries Amygdalinae, subgenus Monocalyptus) and the description of a new species, E. willisii. Australian Journal of Botany 31, 565–584. Ladiges, P.Y., Newnham, M.R. and Humphries, C.J. (1989). Systematics and biogeography of the

G ENE TIC D IVE RSITY

OF

E UCA LYPTS

C H A P T E R

2

Australian ‘green ash’ eucalypts (Monocalyptus). Cladistics 5, 345–364. Ladiges, P.Y., Prober, S.M. and Nelson, G. (1992). Cladistic and biogeographic analysis of the ‘Blue Ash’ eucalypts. Cladistics 8, 103–124. Ladiges, P.Y., Udovic, F. and Drinnan, A.N. (1995). Eucalypt phylogeny—molecules and morphology. Australian Systematic Botany 8, 483–497. Lange, R.T. (1982). Australian Tertiary vegetation. In A History of Australasian Vegetation. (Ed. J.M.B. Smith) (McGraw-Hill: Sydney.) Li, H., Madden, J.L. and Potts, B.M. (1995). Variation in volatile leaf oils of the Tasmanian Eucalyptus species. 1. Subgenus Monocalyptus. Biochemical Systematics and Ecology 23, 299–318. Libby, W.J. and Ahuja, M.R. (1993). Clonal Forestry. In Clonal Forestry II—Conservation and Application. (Eds M.R. Ahuja and W.J. Libby) pp. 1–8. (SpringerVerlag: Berlin.) Mace, B. (1996). Mueller—champion of Victoria’s giant trees. The Victorian Naturalist 113, 198–207. Margules, C.R., Nicholls, A.O. and Austin, M.P. (1987). Diversity of Eucalyptus species predicted by a multivariable environmental gradient. Oecologia 71, 229–232. Marks, G.C. (1979). Review of the host-parasite relations of Eucalyptus spp. infected by Phytophthora cinnamomi Rands. In Phytophthora and Forest Management in Australia. (Ed. K.M. Old) pp. 28–42. (Division of Forest Research, CSIRO: Canberra.) Marks, G.C. and Smith, I.W. (1991). The Cinnamon Fungus in Victorian Forests. Lands and Forests Bulletin No. 31, Department of Conservation and Environment: Melbourne. Marks, G.C., Smith, I.W. and Kassaby, F.Y. (1981). Trunk infection of Eucalyptus species by Phytophthora cinnamomi Rands: a preliminary report. Australian Forest Research 11, 257–267. Martin, H.A. (1978). Evolution of the Australian flora and vegetation through the Tertiary: evidence from pollen. Alcheringa 2, 181–202. Martin, H.A. (1981). The Tertiary flora. In Ecological Biogeography of Australia. (Ed. A. Keast) pp. 391–406. (W. Junk: The Hague.) Martin, H.A. (1982). Changing Cenozoic barriers and the Australian palaeobotanical record. Annals of the Missouri Botanical Gardens 69, 625–667. Martin, H.A. and Gadek, P.A. (1988). Identification of Eucalyptus spathulata pollen and its presence in the fossil record. Memoirs of the Association of Australasian Palaeontologists 5, 311–27. McComb, G., Hinch, J. and Clarke, A.E. (1987). Expression of field resistance in callus tissue inoculated with Phytophthora cinnamomi. Phytopathology 77, 346–351. McComb, J.A., Bennett, I.J., Stukely, M.J.C. and Crane, C. (1991). Selection and propagation of jarrah for

31

D I S E A S E S

A N D

P A T H O G E N S

O F

E U C A L Y P T S

dieback resistance. Combined Proceedings of the International Plant Propagators’ Society 40, 86–90. McComb, J.A., Stukely, M. and Bennett, I. (1994). Future ecosystems—use of genetic resistance. Journal of the Royal Society of Western Australia 77, 179–180. Midgley, S.J., Eldridge, K.G. and Doran, J.C. (1989). Genetic resources of Eucalyptus camaldulensis. Commonwealth Forestry Review 68, 295–308. Mildenhall, D.C. (1980). New Zealand late Cretaceous and Cenozoic plant biogeography: a contribution. Palaeogeography, Palaeoclimatology, Palaeoecology 31, 197–233. Moran, G.F. (1992). Patterns of genetic diversity in Australian tree species. New Forests 6, 49–66. Moran, G.F. and Hopper, S.D. (1987). Conservation of the genetic resources of rare and widespread eucalypts in remnant vegetation. In Nature Conservation: The Role of Remants of Native Vegetation. (Eds D.A. Saunders, G.W. Arnold, A.A. Burbidge and A.J.M. Hopkins) pp. 151–162. (Surrey Beatty and Sons: NSW.) Morrow, P.A., Whitham, T.G., Potts, B.M., Ladiges, P., Ashton, D.H. and Williams, J.B. (1994). Gall-forming insects concentrate on hybrid phenotypes of Eucalyptus hosts. In The Ecology and Evolution of Gall-Forming Insects. (Eds P.W. Price, W.J. Mattson and Y.N. Baranchikov) pp. 121–134. Technical Report NC: 174. (USDA Forest Service: Washington, DC.) Noble, I.R. (1989). Ecological traits of the Eucalyptus L’ Herit. subgenera Monocalyptus and Symphomyrtus. Australian Journal of Botany 37, 207–224. Park, R.F. (1988a). Effect of certain host, inoculum and environmental factors on infection of Eucalyptus species by two Mycosphaerella species. Transactions of the British Mycological Society 90, 221–228. Park, R.F. (1988b). Epidemiology of Mycosphaerella nubilosa and M. cryptica on Eucalyptus spp. in southeastern Australia. Transactions of the British Mycological Society 91, 261–266. Park, R.F. and Keane, P.J. (1982a). Three Mycosphaerella species from leaf diseases of Eucalyptus. Transactions of the British Mycological Society 79, 95–100. Park, R.F. and Keane, P.J. (1982b). Leaf diseases of Eucalyptus associated with Mycosphaerella species. Transactions of the British Mycological Society 79, 101–115. Park, R.F. and Keane, P.J. (1984). Further Mycosphaerella species causing leaf diseases of Eucalyptus. Transactions of the British Mycological Society 83, 93–105. Parsons, R.F. (1969). Distribution and palaeogeography of two mallee species of Eucalyptus in Southern Australia. Australian Journal of Botany 17, 323–330. Parsons, R.F. (1986). Disjunctions in the distribution of Eucalyptus species between Western Victoria and the Mount Lofty-Flinders Ranges area, South Australia.

32

Proceedings of the Royal Society of Victoria 86, 29–34. Parsons, R.F. and Kirkpatrick, J.B. (1972). Possible phantom hybrids in Eucalyptus. New Phytologist 71, 1213–1219. Pederick, L.A. (1979). Natural variation in Shining Gum (Eucalyptus nitens). Australian Forest Research 9, 41–63. Podger, F.D. and Batini, F. (1971). Susceptibility to Phytophthora cinnamomi root-rot of thirty six species of Eucalyptus. Australian Forest Research 5, 9–20. Pole, M. (1989). Early Miocene floras from Central Otago, New Zealand. Journal of the Royal Society of New Zealand 19, 121–127. Pole, M.S. (1993). Early flora of the Manuherikia Group New Zealand. 7. Myrtaceae, including Eucalyptus. Journal of the Royal Society of New Zealand 23, 313–328. Pole, M.S., Hill, R.S., Green, N. and Macphail, M.K. (1993). The Oligocene Berwick Quarry flora— rainforest in a drying environment. Australian Systematic Botany 6, 399–427. Potts, B.M. (1986). The population dynamics and regeneration of a hybrid zone between Eucalyptus risdonii and E. amygdalina. Australian Journal of Botany 34, 305–329. Potts, B.M. (1990). The response of eucalypt populations to a changing environment. Tasforests 2, 179–193. Potts, B.M. and Jackson, W.D. (1986). Evolutionary processes in the Tasmanian high altitude eucalypts. In Flora and Fauna of Alpine Australasia. Ages and Origins. (Ed. B.A. Barlow) pp. 511–527. (CSIRO: Melbourne.) Potts, B.M. and Jordan, G.J. (1994). Spatial pattern and scale of variation in Eucalyptus globulus Labill. ssp. globulus: Variation in seedling abnormalities and early growth. Australian Journal of Botany 42, 471–492. Potts, B.M. and Potts, W.C. (1986). Eucalypt breeding in France. Australian Forestry 49, 210–218. Potts, B.M. and Reid, J.B. (1985). Analysis of a hybrid swarm between Eucalyptus risdonii Hook.f. and E. amygdalina Labill. Australian Journal of Botany 33, 543–562. Potts, B.M. and Reid, J.B. (1988). Hybridisation as a dispersal mechanism. Evolution 42, 1245–1255. Potts, B.M. and Wiltshire, R.J.E. (1997). Eucalypt genetics and genecology. In Eucalypt Ecology: Individuals to Ecosystems. (Eds J. Williams and J. Woinarski) pp. 56–91. (Cambridge University Press: Cambridge.) Potts, B.M., Borralho, N.M.G., Reid, J.B., Cromer, R.N., Tibbits, W.N. and Raymond, C.A. (Eds) (1995a). Eucalypt Plantations: Improving Fibre Yield and Quality. Proceedings of the CRCTHF–IUFRO Conference, Hobart, 19–24 February 1995. (Cooperative Research Centre for Temperate Hardwood Forestry: Hobart.)

M O RP HO LO GY , P HYL OGENY , O R IGIN , D IST R I BU T I ON

A ND

Potts, B.M., Volker, P.W., Hodge, G.R., Borralho, N.M.G., Hardner, C.H. and Owen, J.V. (1995b). Genetic limitations to the exploitation of base populations of Eucalyptus globulus ssp. globulus. In Eucalypt Plantations: Improving Fibre Yield and Quality. Proceeings of the CRCTHF–IUFRO Conference, Hobart, 19–24 February 1995. (Eds B.M. Potts, N.M.G. Borralho, J.B. Reid, R.N. Cromer, W.N. Tibbits and C.A. Raymond) pp. 217–221. (Cooperative Research Centre for Temperate Hardwood Forestry: Hobart.) Prober, S., Bell, J.C. and Moran, G.F. (1990a). A phylogenetic and allozyme approach to understanding rarity in three ‘green ash’ eucalypts (Myrtaceae). Plant Systematics and Evolution 172, 99–118. Prober, S.M., Tompkins, C., Moran, G.F. and Bell, J.C. (1990b). The conservation genetics of Eucalyptus paliformis L. Johnson et Blaxell and E. parvifolia Cambage, two rare species from south-eastern Australia. Australian Journal of Botany 38, 79–95. Pryor, L.D. (1957). Variation in Snow Gum (Eucalyptus pauciflora Sieb.). Proceedings of the Linnean Society of New South Wales 81, 299–305. Pryor, L.D. (1976). The Biology of Eucalypts. (Edward Arnold: London.) Pryor, L.D. and Briggs, J.D. (1981). Australian Endangered Species: Eucalypts. (Australian National Parks and Wildlife Service: Canberra.) Pryor, L.D. and Byrne, O.R. (1969). Variation and taxonomy in Eucalyptus camaldulensis. Silvae Genetica 18, 64–71. Pryor, L.D. and Johnson, L.A.S. (1971). A Classification of the Eucalypts. (Australian National University Press: Canberra.) Pryor, L.D. and Johnson, L.A.S. (1981). Eucalyptus, the universal Australian. In Ecological Biogeography of Australia. (Ed. A. Keast) pp. 499–536. (W. Junk: The Hague.) Pryor, L.D. and Knox, R.B. (1971). Operculum development and evolution in eucalypts. Australian Journal of Botany 19, 143–171. Pryor, L.D., Williams, E.R. and Gunn, B.V. (1995). A morphometric analysis of Eucalyptus urophylla and related taxa. Australian Systematic Botany 8, 57–70. Purnell, R.C. and Lundquist, J.E. (1986). Provenance variation of Eucalyptus nitens on the eastern Transvaal highveld in South Africa. South African Forestry Journal 138, 23–31. Rozefelds, A. (1996). Eucalyptus phylogeny and history: a brief summary. Tasforests 8, 15–26. Sale, M.M., Potts, B.M., West, A.K. and Reid, J.B. (1993). Relationships within Eucalyptus using chloroplast DNA. Australian Systematic Botany 6, 127–138. Sale, M.M., Potts, B.M., West, A.K. and Reid, J.B. (1996). Relationships within Eucalyptus (Myrtaceae) using PCR-amplification and southern hybridisation of

G ENE TIC D IVE RSITY

OF

E UCA LYPTS

C H A P T E R

2

chloroplast DNA. Australian Systematic Botany 9, 273–282. Sampson, J.F., Hopper, S.D. and James, S.H. (1995). The mating system and genetic diversity in the Australian arid zone mallee, Eucalyptus rameliana F. Muell. Australian Journal of Botany 43, 461–474. Singh, G., Kershaw, A.P. and Clark, R. (1981). Quaternary vegetation and fire history in Australia. In Fire and the Australian Biota. (Eds A.M. Gill, R.H. Groves and I.R. Noble) pp. 23–54. (Australian Academy of Science: Canberra.) Specht, R.L. (1996). The influence of soils on the evolution of the eucalypts. In Nutrition of Eucalypts. (Eds P.M. Attiwill and M.A. Adams.) pp. 31–60. (CSIRO: Melbourne.) Steane, D.A., Byrne, M., Vaillancourt, R.E. and Potts, B.M. (1998). Chloroplast DNA polymorphism signals complex interspecific interactions in Eucalyptus (Myrtaceae). Australian Journal of Systematic Botany 11, 25–40. Stone, C. and Bacon, P.E. (1994). Relationships among moisture stress, insect herbivory, foliar cineole content and the growth of river red gum Eucalyptus camaldulensis. Journal of Applied Ecology 31, 604–612. Stukely, M.J.C. and Crane, C.E. (1994). Genetically based resistance of Eucalyptus marginata to Phytophthora cinnamomi. Phytopathology 84, 650–656. Urdovic, F., McFadden, G. and Ladiges, P.Y. (1995). Phylogeny of Eucalyptus and Angophora based on 5S rDNA spacer sequence data. Molecular Phylogenetics and Evolution 4, 247–256. van Wyk, G. (1985). Tree breeding in support of vegetative propagation of Eucalyptus grandis (Hill) Maiden. South African Forestry Journal 135, 33–39. Walker, J. and Bertus, A.L. (1971). Shoot blight of Eucalyptus spp., caused by an undescribed species of Ramularia. Proceedings of the Linnean Society of New South Wales 96, 108–115. Wallace, H. and Trueman, S.J. (1995). Dispersal of seeds of Eucalyptus torelliana by the stingless bee, Trigona carbonaria. Oecologia 104, 12–16. Wardell-Johnson, G., Williams, J.E., Hill, K. and Cumming, R. (1997). Evolutionary biogeography and contemporary distribution of Eucalyptus. In Eucalypt Ecology: Individuals to Ecosystems. (Eds J. Williams and J. Woinarski) pp. 92–128. (Cambridge University Press: Cambridge.) Watson, R.J., Ladiges, P.Y. and Griffin, A.R. (1987). Variation in Eucalyptus cypellocarpa L. Johnson in Victoria, and a new taxon from the Grampian Ranges and Anglesea. Brunonia 10, 159–176. Whitham, T., Morrow, P. and Potts, B.M. (1991). The conservation of hybrid plants. Science 254, 779–780. Whitham, T.G., Morrow, P.A. and Potts, B.M. (1994). Plant hybrid zones as centers of biodiversity: the

33

D I S E A S E S

A N D

P A T H O G E N S

O F

herbivore community of two endemic Tasmanian eucalypts. Oecologia 97, 481–490. Wilcox, M.D. (1982). Preliminary selection of suitable provenances of Eucalyptus regnans for New Zealand. New Zealand Journal of Forestry Science 12, 468–479. Williams, K. and Potts, B.M. (1996). The natural distribution of Eucalyptus species in Tasmania. Tasforests 8, 39–164. Wiltshire, R., Potts, B.M. and Reid, J.B. (1990). Phenetic affinities, variability and conservation status of a rare Tasmanian endemic, Eucalyptus morrisbyi R. G. Brett. In Aspects of Tasmanian Botany—A Tribute to Winifred Curtis. (Eds S.J.S.M.R. Banks, A.E. Orchard and G. Kantvilas) pp. 213–229. (Royal Society of Tasmania: Hobart.)

34

E U C A L Y P T S

Wiltshire, R.J.E., Potts, B.M. and Reid, J.B. (1991). A paedomorphocline in Eucalyptus: Natural variation in the E. risdonii/E. tenuiramis complex. Australian Journal of Botany 39, 545–566. Wiltshire, R.J.E. and Reid, J.B. (1987). Genetic variation in the Spinning Gum, Eucalyptus perriniana F. Muell. ex Rodway. Australian Journal of Botany 35, 33–47. Wolfe, M.S. and McDermott, J.M. (1994). Population genetics of plant pathogen interactions: the example of the Erysiphe graminis-Hordeum vulgare pathosystem. Annual Review of Phytopathology 32, 89–113. Young, N.D. (1996). QTL mapping and quantitative disease resistance in plants. Annual Review of Phytopathology 34, 479–501.

C H A P T E R

G ROWTH H ABITS E UCALYPTS

AND

S ILVICULTURE

OF

3

R.G. Florence

S

U M M A R Y

Since European settlement of Australia, eucalypts have been largely cleared from vast areas for agriculture, and residual eucalypt forests subjected to exploitative harvesting. Over the last 50 years much effort has been devoted to restoring damaged landscapes and to developing sustainable forest management and utilisation procedures. Sustainable silviculture is based on an understanding of the unusual growth habits of eucalypts such as their tiny seeds and vulnerable seedlings which require special seedbeds, and their sensitivity to competition (for light, and soil nutrients and water resources). The various alternative silvicultural methods that have been developed and tested experimentally and in practice are reviewed. New directions in eucalypt silviculture for sustainable production and environmental conservation in native forests, and for production in the rapidly expanding plantations, are discussed.

35

D I S E A S E S

A N D

P A T H O G E N S

O F

3.1 Introduction Over many thousands of years, eucalypts have become adapted to the environmental effects, especially the fire regimes, associated with habitation by Australia’s indigenous peoples. Eucalypt forests have provided the bulk of Australian wood and sawn timber needs since first European settlement in 1788. The early European settlers saw the eucalypt forests and woodlands as an impediment to agricultural development and the forest resource as vast and unlimited. Hence, the forests and woodlands were subject to extensive clearing; elsewhere early logging was essentially exploitative. Recurrent wildfires are a feature of the hot, dry environment of the south-east and south-west forests and these degraded both the unlogged forest and residual trees within the harvested forests. Thus, when formed early in the twentieth century, Australian forest services faced three critical tasks: 1

protecting the forests from fire

2

regulating cutting in order to sustain sawlog supply to industry

3

improving the forest condition by removing the ‘overburden’ of commercially useless trees.

A large part of the more accessible forest had been brought under management in this way by World War II. The demand for timber expanded greatly during the post-World War II decades of rapid economic growth and technological advances in logging. This meant it was now possible to extend logging to the hitherto inaccessible escarpment and mountain forests and to the tall wet sclerophyll (tall open) forests of southern Australia. Generally, these forests were logged at rates well in excess of sustainable yields in order to avoid escalating wood import costs, and to maintain rural industries and communities. The expansion of wood production in this way generated social conflict about the role and management of the native eucalypt forests. This has led, in turn, to the present programs designed to achieve a socially acceptable balance between the production and conservation functions of forests, through the ‘Comprehensive Regional Assessment’ process, and to ensure wood production is sustainable in both ecological and economic terms.

36

E U C A L Y P T S

The development of ecologically sustainable forest management requires both an appreciation of the ecological principles that underpin silvicultural practice and the formulation of silvicultural methods which integrate a wider range of objectives than previously. This chapter develops this theme by examining growth habits of the eucalypts, silvicultural methods that have been used in the eucalypt forests, matters to be considered in formulating ecologically sustainable practice, and silvicultural directions for the forests.

3.2 Growth habits of the eucalypts There are several attributes of eucalypts that determine appropriate silvicultural regimes for the forests. These relate to the requirements for obtaining seedling regeneration (see Chapter 4), the way regrowth responds to competition from residual trees, the effects of species and site on stand dynamic processes, and patterns of stand volume production within even-aged regrowth. These attributes are considered briefly.

3.2.1

The seedbed for seedling regeneration

Regeneration may occur within the eucalypt forest where an opening of sufficient size has been created within the canopy. Regeneration develops from newly establishing seedlings, existing lignotubers and other advance growth or from coppice. New seedlings will normally establish and develop in useful quantities only where there has been sufficient disturbance to the forest floor to expose soil and create a biological environment in the soil favourable for rapid seedling development. A wildfire or a prescribed slash-disposal burn will create such a seedbed. A seedbed may also be produced where the soil has been exposed and disturbed by machinery working during or after logging. A disturbed seedbed is needed as eucalypt seed is small, there is no endosperm and the radicle needs to find its way quickly into moist soil in order to take up water and nutrients. Even when the radicle reaches soil, further seedling growth may be restricted by an unfavourable biological condition that has been noted in many eucalypt forests soils. Within blackbutt (Eucalyptus pilularis) forest this has been attributed by Florence and Crocker (1962) to the long-term incorporation into soil of the more

G R OW T H H A BITS

refractory (lignified) components of nutritionally poor litter, leading to a decline in the availability of microbial energy sources, low microbial diversity, the dominance of inhibitory soil organisms [e.g. Cylindrocarpon destructans (Zinssm.) Scholten; Evans et al. 1967] and a breakdown in normal processes of nutrient mineralisation. Ashton and Willis (1982) also implicated several soil biological factors in the poor development of E. regnans seedlings in undisturbed forest soil. These include leachates from insect frass, difficulties in competing for a limited pool of ammonium ions before the seedling root has developed a mycorrhizal association, the inhibiting influence of the ubiquitous Cylindrocarpon destructans, and contact between plant roots and lipids in the soil. Waxy lipids of cuticular origin make up as much as 16% of the organic matter in the soil of E. regnans forests. Again, from studies on high altitude soils in Tasmania, it was concluded that ‘late successional’ vegetation is ‘antagonistic’ to eucalypt seedlings through progressive and increasingly unfavourable changes in the soil biological condition with increasing time since fire (Ellis and Pennington 1992). The response of the eucalypt seedlings may have much to do with the effect of fire on the biological condition of the soil. Following an intense fire, an increase in soluble carbon within the soil organic matter will stimulate soil microbial processes, and release nutrients through soil mineralisation (‘the partial sterilisation effect’). Soil heating or drying may also directly affect the microbial populations in the soil. Launonen et al. (1999) suggest that undried and unheated forest soil adversely affects development of effective mycorrhizas on the roots of E. regnans. Whatever the cause, a seedbed favourable for the establishment and vigorous growth of new seedlings is created by fire. Mechanical disturbance of the litter and mineral soil may have an effect on biological processes within the soil comparable to that of fire, providing an alternative means of creating an effective seedbed.

3.2.2

Sensitivity to competition

A dominant eucalypt may be an aggressive competitor for site resources, but where the same species is in a subordinate stand position, it can be highly sensitive to competition. By world standards, eucalypts would be classed as ‘intolerant’ to ‘very intolerant’ of competition. Eucalypts cannot develop

A ND

S ILVICULTURE

OF

E UCA LYPTS

C H A P T E R

3

strongly where the amount of light reaching the leaves is reduced appreciably, or where access to water and nutrients is limited by competition from overtopping or adjacent trees (root competition). Because there is some range in tolerance of competition, there is a tendency to refer to ‘intolerant’ and ‘tolerant’ eucalypts. However, no eucalypt can be classed as ‘tolerant’ in terms of recognised criteria for trees in this category (Jacobs 1955; Florence 1996). It may be more appropriate to refer to some eucalypt species as ‘intolerant but persistent’ rather than ‘tolerant’. Eucalypts do not develop crowns with dense foliage, conforming with the general criterion that intolerant species have thin foliage and open crowns and canopies (Daniel et al. 1979). The intolerance of the eucalypt may also be evident through the accumulation of ‘growth restricted’ trees in the forest, particularly on sites of low to moderate quality. Trees growing in close proximity may bend away from each other, lignotuberous seedlings responding to a small canopy opening may develop weak and unbalanced crowns, and where there is abrasion between the crown of a subordinate tree and the overwood canopy, continuing apical growth ceases. While trees may persist in a growth restricted condition for some time, they quickly lose the capacity to respond appreciably to release.

3.2.3

Growth rates, crown segregation and self-thinning

Compared with many other tree species, most eucalypts are capable of rapid early height growth. This is a particular characteristic of the more intolerant eucalypts such as E. camaldulensis, E. grandis and E. regnans. Within stands of vigorous, fast-growing, intolerant species on high quality sites, there will normally be rapid segregation of stems into dominance or crown classes, and rapid reduction in stocking as suppressed trees die (‘self-thinning’). The death of suppressed trees provides a food base for wood rotting fungi in such native forests (see Chapters 12 and 13). Stands of E. delegatensis, E. diversicolor, E. globulus, E. grandis and E. regnans will self-thin rapidly. For example, the stocking of E. regnans regrowth might decline from around 1700 live stems per hectare at eight years of age to 400 by age 40 (Ashton 1976). Expression of dominance within the canopy trees is not as strong in E. pilularis and E. sieberi stands on

37

D I S E A S E S

A N D

P A T H O G E N S

O F

sites of average quality, and hence the rate of selfthinning is less. The rate of self-thinning of the slower growing or more tolerant or persistent eucalypts will be lower still. For example, the stocking of an E. obliqua stand had declined from 22,000 stems per hectare at age seven to 7000 at age 18 (Borough et al. 1978), far more than the anticipated stocking of around 1300 stems per hectare in an E. regnans stand at the same age.

3.2.4

Volume growth patterns

Eucalypt species also differ appreciably in patterns of stand volume production, often reflecting the relative tolerance and early vigour of the species (Florence 1996). Stands of faster growing eucalypts may have a particularly rapid early growth phase, reaching an early peak in current annual volume production (Current Annual Increment, CAI). For example, on a high quality site, the peak in CAI for E. globulus may be around 12 years when 50 to 60 cubic metres per hectare per annum of wood volume will be produced. However, by 30 years, the CAI will have declined to around 20 cubic metres per hectare per annum. Eucalyptus regnans may not reach a peak in CAI until around 20 years, but at this point a high annual volume production will be achieved. The growth pattern of E. pilularis is similar to that of E. regnans, but the volume of wood produced is much less. The more tolerant or persistent eucalypt species will not only be slower growing than the intolerant species, but also they will lack the distinctive rapid growth phase and early production peak of the fast growing species. Thus, the volume production of an E. obliqua stand on a relatively dry site will build up slowly to only 15 cubic metres per hectare per annum by age 20 to 25 years. However, it will maintain that production over a much greater time than the fast-growing intolerant species. In this way the annual volume production of a 60-year old to 90-year-old E. obliqua stand may exceed that of an E. regnans stand of the same age.

3.3 Sivicultural practice in natural forests The many silvicultural systems or methods described in the literature can be thought of as representing a gradational series in the extent to which the forest floor is exposed to solar radiation and wind, in the degree of root competition to which the developing

38

E U C A L Y P T S

seedlings are subjected and in the supply of seed from the residual stand. The series can be represented by the selection, shelterwood and clearfelling methods, although it is not always possible to place a silvicultural practice into one of these conventional categories.

3.3.1

Selection method

The selection method involves removal at any one harvest of only part of the existing growing stock. The method is normally, although not invariably, applied where there is a range of tree sizes and ages already present within the stand. In its classic or ‘narrow’ sense, the selection method involves the maintenance of a high level of growing stock, a near complete range of tree ages on each hectare of forest, and harvest of sawlogs and thinnings on a short cutting cycle. Because of their growth habits, the eucalypt forests are not amenable to the classic selection system. In Australian practice, the term is applied in a much broader sense, that is, to almost any harvest that creates or maintains some range in tree ages. The method often involves the removal of trees in patches or groups large enough to produce conditions similar to those associated with clearfelling or shelterwood methods. Management of native forests in two States (New South Wales, Queensland) has been based predominantly on selection-type silviculture. Initially, selection was based on ‘diameter-limit cutting’, which involved harvesting only those trees above a prescribed diameter. This was later modified by creating specific openings (or groups) within the forest to encourage regeneration of preferred species in even-aged patches (the ‘Australian Group Selection System’) (Jacobs 1955; Florence 1996). From the 1970s greater industry acceptance of smaller and more defective trees permitted an important modification to the selection prescription. Tree marking could now focus on the retention of trees with good growth potential through a range of sizes, and the harvest of substandard trees that would previously have been retained. This achieved the short-term objectives of sustaining sawlog supply to industry from a limited resource, improving productivity of the growing stock and maintaining a good level of structural and biological diversity throughout the forests. While highly effective use of existing growing stock has been achieved in this way, since the 1970s little emphasis was placed on stand

G R OW T H H A BITS

regeneration or on establishment of the full range of size classes needed to service industry needs in the long term. It is difficult to maintain full site stocking under the selection method, particularly where the forest is ecologically diverse. More positive steps are needed to ensure complete site regeneration, particularly where the forests continue to be managed in a conservative way.

3.3.2

The shelterwood method

The shelterwood method traditionally has been applied where species require protection from climatic extremes at the regeneration phase (low temperatures, high levels of insolation, strong winds). Under this method the mature timber is removed in a series of cuttings extending over a relatively short part of the rotation, and essentially even-aged regeneration is established under the partial shelter of the residual overwood. Under Australian conditions the shelterwood method has been used in its classic sense only on the high altitude plateaux in northern and central Tasmania where regrowth develops poorly in response to clearfelling (Keenan and Candy 1983; Webb et al. 1983; Ellis et al. 1985; Keenan 1986; Battaglia and Wilson 1990). The term has been used elsewhere in Australia where a shelterwood-type pattern of cutting aims to meet several other objectives, for example, continuing wood increment on the higher quality trees of the stand (Squire and Edgar 1975) and the accumulation of lignotuberous and other advance growth before the final harvest of the overwood (Bradshaw 1986).

3.3.3

Clearfelling

Clearfelling involves removal of all useable elements of the stand, thus increasing site exposure to the maximum and decreasing root competition to the minimum. The technology for large coupe clearfelling was developed in the 1950s and 1960s in Tasmania (Gilbert 1958), Victoria (Cunningham 1960) and Western Australia (White 1971), primarily to cope with the tall wet sclerophyll forests of the temperate region where the species are among the most intolerant of the eucalypts, and intensive seedbed preparation is essential. Clearfelling is by far the most technically efficient method for harvesting and regenerating these forests. An intense slash-disposal burn following clearfelling is widely used to produce a seedbed and to reduce

A ND

S ILVICULTURE

OF

E UCA LYPTS

C H A P T E R

3

the sometimes massive accumulation of logging slash. A seedbed may also be created by mechanically disturbing a large proportion of the surface soil within a logging coupe. Mechanical site disturbance may be more costly than slash burning within larger coupes but can be a viable alternative to slash burning on most sites. The seed source for regeneration may be provided by residual trees retained at a suitable spacing (the ‘seed tree’ method) or seed may be collected and sown onto a disturbed forest floor. Direct seeding may be more expensive but, operationally, is generally more efficient. Planting of nursery raised seedling stock is another option and is used, for example, as one strategy for regenerating the E. diversicolor forest of Western Australia. Clearfelling practice has been subject to continuing investigation in order to develop more efficient clearfelling and seeding technologies and alternative silvicultural methods. The development of more efficient technologies has involved investigation of the effect of seed provenance and appropriate seeding mixtures (Forestry Commission of Tasmania 1991a), seed treatment (Neumann and Kassaby 1986), aerial sowing of seed (Forestry Commission of Tasmania 1991b; Wilson 1993), and different coupe sizes and seedbed preparation methods as well as the relative costs of using helicopters and fixed wing aircraft in seed distribution (King 1991; Wilson 1993; Sharp 1993). Studies on alternative silvicultural methods have been a response to environmental concerns about the effects of clearfelling. For example, Victoria’s ‘Silvicultural Systems Project’ (Squire et al. 1987) has compared clearfelling with seed tree, group selection, shelterwood and strip felling regimes in several forest types. This has demonstrated clear limits to the use of alternative methods in tall wet sclerophyll forest. A range of environmental stresses affect plants in gaps less than about one to two hectares, resulting in suppression and death of seedlings (Walters 1991). Moreover, there are serious operational problems including operational health and safety concerns associated with alternative methods in these forests (King and Cook 1992; Mitchell 1993; Burgess 1993; Dignan 1993). It has been possible to modify the practice of clearfelling in more open forests. Within the Eden area of New South Wales some tree components are

39

D I S E A S E S

A N D

P A T H O G E N S

O F

retained in cut-over coupes, including saplings, poles, larger trees with sawlog potential, seed trees and wildlife habitat trees. In Tasmania, diversity in silvicultural practice is based on structural diversity within the forest, particularly the presence of trees with sawlog potential and useful patches of advance growth (saplings and poles). Similarly, in Victoria’s Otway Ranges, substandard trees may be retained within the coupe where there is no market for pulpwood, and there is environmental benefit in so doing (Bartlett 1983).

3.4 Ecologically sustainable silviculture The major influences on silvicultural practice have been the priority given to maintenance of wood supply for the short term (e.g. through selection regimes), and achievement of technically efficient and low-cost harvesting and regeneration operations (through clearfelling regimes). While these wood supply strategies have served Australia well, circumstances relating both to wood supply and forest management have changed. Now, environmental conservation has become a dominant factor in forest management, and appropriate silvicultural methods need to be developed to address this. There are two requirements for silvicultural practice that need to be met: 1

ecological sustainability

2

an ability to respond to a wider range of social and economic circumstances.

The concept of ‘ecological sustainability’ provides the foundation upon which modern forest management needs to be built. This envisages that the naturally occurring species and community patterns will be maintained within the forest, that soil resources will not be depleted to such an extent that the health and productivity of a forest will be jeopardised, that ecosystem processes will be consistent with those of the natural forest environment and that susceptibility to pests and diseases will not be increased.

3.4.1

Natural species and community patterns

Until the 1960s, conventional wisdom held that fire frequency was the primary factor that created ecological patterns in the Australian forests. While there are more specialised situations where fire is

40

E U C A L Y P T S

very important, for example, in the vegetation of the peat soils in south-west Tasmania (Brown and Podger 1982) and the high elevation forest in the same State (Ellis 1985), under most circumstances the pattern represents the outcome of a sensitive ‘ecological sifting’ of species by several site factors (Florence 1981). Within the one forest, eucalypt subgenera and species will be responding to variations in soil fertility, physical properties of soils affecting water storage and availability (which in turn may affect pathogen activity), aspect (through differences in evapotranspiration and soil depth), and position on slope (integrating soil fertility, shelter, water status and, in some situations, the activity of pathogens in the soil). An appreciation of these complex species–site relationships may place constraints on the extent to which the distributions of commercially preferred species might be extended beyond the immediate limits of their natural occurrences, or their frequencies greatly increased within mixed species communities. Where site disturbance is not excessive, and no attempt has been made to alter the species composition, community patterning within the eucalypt forest appears to be robust and resistant to change. The control exerted by site factors on the distribution and association patterns of species might be expected to buffer the forest against undue changes in those patterns. Concerns about the ecological consequences of more radical silvicultural practices (e.g. clearfelling, burning, direct seeding) may be valid where there is little opportunity for ecological sifting of species within the regrowth. This could happen, for example, within a mixed species forest where a single preferred species is encouraged under a seed tree or direct seeding regime, and where there is little advance growth of other species, or that advance growth was largely destroyed in an intense slash-burn.

3.4.2

Forest structure

Although the structure of the natural eucalypt forest and its influence on the health, dynamics and productivity of the forest has been little considered in the silvicultural literature, there are circumstances where this may be important. It has been widely held that before European settlement occasional fires of great intensity maintained eucalypt forests in an even-aged condition. This may be largely true where stands of

G R OW T H H A BITS

fire sensitive species are killed and replaced within a few years by vigorous, even-aged regrowth, but even in these forests individual mature to senescent trees or patches of trees would normally survive a wildfire. Alternatively, where the species are more fire resistant (and this includes the greater number of eucalypts), regrowth may have developed occasionally within gaps created by the death or senescence of individual trees or small patches of trees. In this case the natural forest would have been uneven-aged, although this might be obscured by the way large-boled trees remain in mature to senescent growth stages for 200 years or more. Where an uneven-aged forest is clearfelled and regenerated, the even-aged regrowth will make a much greater demand on site resources than the natural forest subject only to progressive gap-phase replacement. This demand will be particularly great at the time of peak annual volume production, for example, 20 to 40 years after clearfelling. Where this demand cannot be met from the site resources, expression of dominance within the developing stand might be weak, and the rate of self-thinning slow. There could be circumstances where the forest also becomes susceptible to decline, diseases and dieback as seen in some of the diseases of complex etiology (see Chapter 17).

3.4.3

Loss of nutrients

Inevitably, wood harvesting and the use of an intense fire to create a seedbed will result in loss of part of the nutrient capital of the site. These losses may be compensated for, wholly or in part, by natural inputs to the site where the stand is largely undisturbed during the subsequent rotation. There will also be important inputs of nitrogen through biological fixation by free-living bacteria in the soil and by nodulated plants, particularly in the early fire successional stage which in eucalypt forests is often dominated by Acacia and other nodulated species. Only a small amount of nitrogen is fixed annually in dry sclerophyll forest (e.g. 0.1–1.6 kg/ha in E. marginata forest, Hansen et al. 1987). In contrast, 10 kilograms per hectare was added to an E. pauciflora forest (Raison et al. 1993), and 14 kilograms per hectare to a mature E. diversicolor forest (Grove and Malajczuk 1992). The critical questions concerning these processes are: will nutrient inputs balance outputs over the rotation,

A ND

S ILVICULTURE

OF

E UCA LYPTS

C H A P T E R

3

and if not, will the deficit lead to any reduction in site productivity in the short or long term? There have been several nutrient balance sheets produced for harvested eucalypt forests in Australia. One for an E. regnans forest (Stewart et al. 1985) is based on the effects of clearfelling, an intense slashburn to prepare a seedbed, and a 50-year regrowth rotation. Despite the severity of this regime, net losses of nitrogen and phosphorus were estimated to be relatively small (around 400 kg/ha of N and 4 kg/ha of P, compared with the total available reserves of these elements of 7876 and 323 kg/ha, respectively). Both the available nutrient reserve and the harvesting losses will be smaller within mixed species forest of lower site quality (Turner and Lambert 1986; Stewart et al. 1990). However, the proportionate loss of nutrient capital will be greater on lower quality sites, for example, 18% of the ‘forest accessible’ soil phosphorus. This suggests the lower quality forest might not be as resilient as the higher quality forest in the long term, and should be managed more conservatively in order to avoid any breakdown in ecosystem processes, stand stagnation or increased susceptibility to pests and diseases.

3.4.4

Plant successional processes

Plant and soil processes associated with the early stages of secondary succession, particularly following a fire, may contribute to the long-term health, productivity and stability of a forest. Nitrogen-fixing species commonly make up a large part of the postfire community, and these will contribute, in time, to the organic matter and nitrogen content of the soil. Where the successional crop is dense, it will also help protect the exposed soil from erosion, and take up rapidly the soluble nutrients released in appreciable quantities following a fire. Subsequently, the postfire successional species will cycle a number of nutrients important in eucalypt nutrition, accelerate the decomposition of the eucalypt litter and, through the greater nutrient status of the soil organic matter, help maintain a more diverse and active soil microflora. It follows that periodic fire of at least moderate intensity could help maintain the health and productivity of the eucalypt forest. For example, it has been argued that occasional moderate to intense fire in jarrah (E. marginata) forest can stimulate the development of a crop of the nitrogen-fixing Acacia pulchella R.Br. and, through this, either directly inhibit the root pathogen Phytophthora cinnamomi

41

D I S E A S E S

A N D

P A T H O G E N S

O F

E U C A L Y P T S

Rands, or restrict its spread and activity through the influence of the acacia on the biological condition of the soil (Shea and Kitt 1976) (see Chapter 19).

3.4.5

Pests and diseases

The decline, dieback and death of trees in eucalypt forests will sometimes be a consequence of historical events that have exposed the environmental threshold of a species or plant community. For example, ‘southern regrowth dieback’ in Tasmania (Podger et al. 1980) (see Chapter 17) and Armillariaassociated death of trees in central Victoria (Edgar et al. 1976; Kile 1981) (see Chapter 12), both involving species of the Eucalyptus subgenus Monocalyptus, might have their origins in unusually severe disturbances to natural ecosystems, the subsequent development of highly stocked even-aged stands and limiting site resources to support them (Florence 1996). Thus, in evaluating any incidence of stand decline or disease, it is necessary to take account of the ecological relationships between species and sites, historical influences on the forest, changes in stand structure these may have generated, and the current stand dynamic processes and tree crown conditions.

delineation of protected and special management zones within the multiple use forest, through greater diversity in silvicultural practice within general wood production zones, and through adoption of silvicultural practices which mimic natural processes in the forests. As a result, natural levels of genetic and structural diversity could be maintained within the forests, thus contributing to avoidance of problems of decline and dieback and outbreaks of pests and diseases, at least on a wide scale. Greater silvicultural diversity will mean determining an appropriate practice for each unit of forest which is more or less homogeneous in composition, structural components and growing stock condition. Biological and structural diversity throughout a forest which has been subject conventionally to a clearfelling regime might be enhanced in the following ways. 1

Planning across the landscape—it is appropriate to plan protection zones, coupe size and shape, and tree and community retention patterns across the landscape. For example, the use of a standard coupe design over a large area might be questioned where wildlife conservation is a management objective, and animals have different habitat requirements, home ranges and minimum population sizes. The retention of wildlife corridors between unlogged areas may have to be considered.

2

Protection of specific patches of vegetation within coupes—patches of forest of some vegetational or structural interest might be recognised and protected within coupes (e.g. patches of lower slope forest, or patches with an interesting aspect effect or with a high level of species complexity or diversity).

3

General tree retention within coupes—trees and associated understorey may be retained where appropriate (e.g. where light to moderate regeneration burns or mechanical site disturbance can be used). This may include useful advance growth, larger trees that might make sawlogs at a future harvest, seed trees and wildlife habitat trees. These patterns might be arranged so that unimpeded development of substantial areas of eucalypt regrowth is provided.

Similarly, an enhanced susceptibility of the forest to insect attack may reflect excessive disturbance to forest ecosystems, changes in natural species patterns and frequencies (including changes in populations of predators), loss of plant diversity and decline in the health and vigour of trees (Florence 1996). With current knowledge of, and further research into, patterns and processes in eucalypt forests, it should be possible to recognise those situations where problems may arise and establish the silvicultural and operational limits within which production forestry can be practised without increasing the incidence and severity of pests and diseases.

3.5 New directions in silviculture Silvicultural practice needs to be not only ecologically sustainable but also responsive to a much wider range of circumstances than previously. Notably, conservation objectives embodied in the National Forest Policy Statement (Commonwealth of Australia 1992) and Regional Forest Agreement documents (e.g. Independent Expert Working Group 1998) will be fully realised only where the wood production forest makes a significant contribution to environmental conservation. This can be achieved through the

42

G R OW T H H A BITS

4

Diversity in seedbed preparation—diversity within the understorey may be maintained where several methods are used to create seedbeds (e.g. slash fires of varying intensity and mechanical disturbance of the forest floor and soil).

5

Silviculture for wet sclerophyll forest—it will be more difficult, but not impossible, to develop areas of productive regrowth within the taller wet sclerophyll forest, and yet maintain some biological and structural diversity throughout the forest. Individual trees, or patches of trees, might be left undisturbed during harvesting. In some circumstances the overwood within a mixed eucalypt–rainforest community might be selectively harvested, and the stand left unburnt (favouring growth of temperate rainforest species), or lightly burned in a mosaic pattern to encourage patches of eucalypt regrowth within a vegetationally diverse forest (Hickey and Wilkinson 1994).

6

7

Use of several silvicultural methods—greater ecological and structural diversity might be sought by using several distinct silvicultural methods rather than simply modifying the one (clearfelling) method. There will inevitably be some structural diversity within previously uncut or lightly cutover forests, providing a framework within which use of alternative silvicultural methods might be considered. Silviculture within even-aged regrowth—some diversity in silvicultural practice will be appropriate within large areas of even-aged regrowth. Silvicultural diversity might be based on a careful appreciation of diversity in stand conditions. Some sections may be retained (and thinned if possible) to provide high quality sawlogs for the future, others harvested under shelterwood or patch cutting regimes, and yet others clearfelled and re-established immediately. Not only will greater structural and environmental diversity be created in this way, but the forest may continue to meet the demand for a wider range of forest products, including those at the high-quality end of the market.

3.6 Eucalypt plantations There is a widespread perception that just as we have developed a large plantation softwood resource in Australia, so might we also develop a large

A ND

S ILVICULTURE

OF

E UCA LYPTS

C H A P T E R

3

hardwood plantation program in order to enhance prospects for conserving native forests. However, the extent to which this is possible may be subject to both ecological and economic constraints. The ubiquity of eucalypts in Australia, and their occupancy of an infertile and largely arid land, may obscure the fact that the eucalypt can be more site demanding than Pinus and other coniferous taxa, at least in terms of producing forests of commercial quality. The eucalypt has been described as a ‘drought tolerant mesophyte’ (Florence 1981). This means it must open stomata and transpire for some part of each day, and must be able, through various means, to tolerate the consequences of this. Eucalypt species differ in their capacities to regulate water use or to ‘maximise access to water supply’. This is an important factor contributing to the complexity of species and community patterns within the forests. The more productive species are normally those with inherently fast early rates of growth, relatively early peaks in stand volume production, and consequently high rates of water use. Because of their attributes, these species may occupy only sites within the vegetation and environmental mosaic which have adequate rainfall, soil water storage capacity and shelter from excessive insolation and wind. It follows that planting of eucalypts, particularly for sawlogs, may be justified economically only where faster growing species are used, and ecologically, only where sites are generally consistent with those of their natural environments. There can be some site flexibility with the more environmentally tolerant of the faster growing species (mainly species of Eucalyptus in the subgenus Symphyomyrtus) but tree form, bole quality and site production of any species may be adversely affected, and susceptibility to pests and diseases increased, where species are planted too far off-site. For example, where the Monocalyptus species, E. pilularis, is planted off-site, it becomes more susceptible to termite attack and the early formation of a central ‘pipe’ (Greaves and Florence 1966). And although E. globulus appeared to have wide environmental tolerance when planted on the dry Mediterranean coast of southern Spain, it was all but decimated by the introduced insect Phoracantha semipunctata (Fabricius) as demands on site water resource grew and drought stress developed. Hence, where rainfall and edaphic factors are likely to limit growth, it could be better to err on the side of

43

D I S E A S E S

A N D

P A T H O G E N S

O F

caution in selecting species for planting, at least until there is experience of the performance of species extending over a substantial part of a proposed rotation. This becomes especially critical where sawlog production is planned.

3.7 Conclusion The long-term role in wood production of native forests, particularly the more environmentally significant of those forests, remains uncertain. What is certain, however, is that a diverse and viable forest industry will be possible only where a socially acceptable balance between the production and conservation functions of the forests is established. Undoubtedly, the management of the native forests is moving in this direction, although whether far or fast enough remains a matter of debate. Most silvicultural regimes and harvesting practices are now designed to minimise adverse environmental effects, and to achieve some level of biological, structural and aesthetic diversity throughout the forest. Nevertheless, there is still some way to go in generating public confidence that harvesting of the forest is consistent with multiple use objectives and principles of ecologically sustainable forest management. An extension of more basic ecological research is needed to firmly underpin the case for continuing wood production within native forests. This is despite the fact that the greater part of the forests appears to be ecologically robust and free of epidemic disease. If this is to continue, it will be essential to appreciate, much more than we do currently, the ‘environmental threshold’ of the more site-sensitive species and communities, and the extent to which tree decline and expression of disease may be a consequence of historical events that have exposed that threshold. Thus, ecologically sustainable silviculture demands a more critical understanding of the relationships between the composition and structure of forest stands, the availability of site resources to those stands, the effects of logging and fire on those resources, and the continuing health, dynamics and productivity of the regrowth forests.

3.8 References Ashton, D.H. (1976). The development of even-aged stands of Eucalyptus regnans F. Muell. in central Victoria. Australian Journal of Botany 24, 397–414.

44

E U C A L Y P T S

Ashton, D.H. and Willis, E.J. (1982). Antagonisms in the regeneration of Eucalyptus regnans in the mature forest. In The Plant Community as a Working Mechanism. (Ed. E.I. Newman) pp. 113–128. Special Publications Series of the British Ecological Society. (Blackwell Scientific Publications: Oxford.) Bartlett, A.G. (1983). Multiple use hardwood forest management in the Otway Ranges. Australian Forestry 46, 278–286. Battaglia, M. and Wilson, L.P. (1990). Effect of shelterwoods on stocking and growth of regeneration in dry high altitude Eucalyptus delegatensis. Australian Forestry 53, 259–265. Borough, C.J., Incoll, W.D., May, J.R. and Bird, T. (1978). Yield statistics. In Eucalypts for Wood Production. (Eds W.E. Hillis and A.G. Brown) pp. 201–205. (CSIRO: Melbourne.) Bradshaw, F.J. (1986). Silvicultural guidelines for virgin southern jarrah forest. Technical Report No. 4. (Department of Conservation and Land Management, Western Australia: Perth.) Brown, F.J. and Podger, F.D. (1982). Floristics and fire regimes of a vegetation sequence from sedgelandheath to rainforest at Bathurst Harbour, Tasmania. Australian Journal of Botany 30, 659–676. Burgess, J.S. (1993). A block level simulation study of the application of single silvicultural systems. VSP Internal Report No. 15. (Department of Conservation and Natural Resources, Victoria: Melbourne.) Commonwealth of Australia (1992). National Forest Policy Statement. December 1992. (Government Printer: Canberra.) Cunningham, T.M. (1960). The natural regeneration of Eucalyptus regnans. Bulletin No. 1. (School of Forestry, University of Melbourne: Melbourne.) Daniel, T.W., Helms, J.A. and Baker, S.F. (1979). Principles of Silviculture. McGraw Hill Series in Forest Resources. (McGraw-Hill: New York.) Dignan, P. (1993). Wood production in mountain ash forests: implications of alternative systems for harvesting operations. VSP Technical Report No. 22. (Department of Conservation and Natural Resources, Victoria: Melbourne.) Edgar, J.G., Kile, G.A. and Almond, C.A. (1976). Tree decline and mortality in a selectively logged eucalypt forest in central Victoria. Australian Forestry 39, 288–303. Ellis, R.C. (1985). The relationship among eucalypt forest, grassland and rainforest in a highland area in northeastern Tasmania. Australian Journal of Ecology 20, 297–314. Ellis, R.C. and Pennington, P.I. (1992). Factors affecting the growth of Eucalyptus delegatensis seedlings in inhibitory forest and grassland soils. Plant and Soil 145, 93–105. Ellis, R.C., Webb, D.C., Graley, A.M. and Rout, A.F. (1985). The effect of weed competition and nitrogen

G R OW T H H A BITS

nutrition on the growth of seedlings of Eucalyptus delegatensis in a highland area of Tasmania. Australian Forest Research 15, 395–408. Evans, G., Cartwright, J.B. and White, N.H. (1967). Nectrolide, a phytotoxic compound produced by some root surface isolates of Cylindrocarpon radicicola. Plant and Soil 26, 253–260. Florence, R.G. (1981). The biology of the eucalypt forest. In The Biology of Australian Plants. (Eds J.S. Pate and A.J. McComb) pp. 147–180. (University of Western Australia Press: Perth.) Florence, R.G. (1996). Ecology and Silviculture of Eucalypt Forests. (CSIRO: Melbourne.) Florence, R.G. and Crocker, R.L. (1962). Analysis of blackbutt (Eucalyptus pilularis Sm) seedling growth on a blackbutt forest soil. Ecology 43, 670–679. Forestry Commission of Tasmania (1991a). Eucalypt seed and sowing. Technical Bulletin No. 1. (Native Forest Silviculture: Hobart.) Forestry Commission of Tasmania (1991b). Aerial Sowing Manual. (Forestry Commission of Tasmania: Hobart.) Gilbert, J.M. (1958). Eucalypt-rainforest relationships and the regeneration of the eucalypts. Report of work carried out under the first Australian Newsprint Mills Forestry Fellowship 1955–58. (Forestry Commission of Tasmania: Hobart.) Greaves, T. and Florence, R.G. (1966). Termite incidence in living blackbutt regrowth and possible relations of termite attack to soil properties and tree vigour. Australian Forestry 30, 153–161. Grove, T.S. and Malajczuk, N. (1992). Production and nitrogen fixation (acetylene reduction) by an understorey legume (Bossiaea laidlawiana) in eucalypt forest. Journal of Ecology 80, 303–314. Hansen, A.P., Pate, J.S., Hansen, A. and Bell, D.T. (1987). Nitrogen economy of post-fire stands of shrub legumes in jarrah (Eucalyptus marginata Donn ex Sm) forest in S.W. Australia. Journal of Experimental Botany 38, 26–41. Hickey, J.E. and Wilkinson, G.R. (1994). Silvicultural options for the maintenance of biodiversity in mixed forest used for wood production in Tasmania. Abstract in Conserving Biological Diversity in Temperate Forest Ecosystems—Towards Sustainable Development. (Centre for Resource and Environmental Studies, Australian National University: Canberra.) Independent Expert Working Group (1998). Assessment of management systems and processes for achieving ecologically sustainable forest management in New South Wales. NSW CRA/RFA Steering Committee Project NA 18/ESFM. (Department of Urban and Regional Planning: Sydney.) Jacobs, M.R. (1955). Growth Habits of the Eucalypts. (Government Printer: Canberra.)

A ND

S ILVICULTURE

OF

E UCA LYPTS

C H A P T E R

3

Keenan, R.J. (1986). Review of the shelterwood system and its potential for application in Tasmanian eucalypt forests. Australian Forestry 49, 226–235. Keenan, R.J. and Candy, S. (1983). Growth of young Eucalyptus delegatensis in relation to variation in site factors. Australian Forest Research 13, 197–205. Kile, G.A. (1981). Armillaria luteobubalina: a primary cause of decline and death of trees in mixed species eucalypt forest in central Victoria. Australian Forest Research 11, 63–77. King, M.R. (1991). An evaluation of regeneration costs under alternative silvicultural systems in mountain ash forests. Silvicultural Systems Project. (Department of Conservation and Environment, Victoria: Melbourne.) King, M. and Cook, J. (1992). The regeneration of Eucalyptus regnans under alternative silvicultural systems. 2. Seedbed descriptions. Value Adding and Silvicultural Systems Program, Internal Report No. 7. (Department of Conservation and Environment, Victoria: Melbourne.) Launonen, T.M., Ashton, D.H. and Keane, P.J. (1999). The effect of regeneration burns on the growth, nutrient acquisition and mycorrhizae of Eucalyptus regnans F.Muell. (mountain ash) seedlings. Plant and Soil 210, 273–283. Mitchell, K. (1993). Safety of forest harvesting under alternative silvicultural systems in mountain ash forest. Silvicultural Systems Project, VSP Technical Report No. 21. (Department of Conservation and Natural Resources, Victoria: Melbourne.) Neumann, F.G. and Kassaby, F.Y. (1986). Effects of commercial pesticides in seed coats on seeds and germinants of Eucalyptus regnans, and their potential as seed protectants in the field. Australian Forest Research 16, 37–50. Podger, F.D., Kile, G.A., Bird, T., Turnbull, C.R.A. and McLeod, D.E. (1980). An unexplained decline in some forests of Eucalyptus obliqua and E. regnans in southern Tasmania. Australian Forest Research 10, 53–70. Raison, R.J., O’Connell, A.M., Khanna, P.K. and Keith, H. (1993). Effects of repeated fires on nitrogen and phosphorus budgets and cycling processes in forest ecosystems. In Fire in Mediterranean Ecosystems. (Eds L. Trabaud and R. Prodon) pp. 347–363. Report 5. (Environmental Research Program of the Commission of European Communities: Brussels.) Sharp, R. (1993). Regeneration costs under alternative silvicultural systems in lowland sclerophyll forest. VSP Technical Report No. 9. (Department of Conservation and Natural Resources, Victoria: Melbourne.) Shea, S.R. and Kitt, R.J. (1976). The capacity of jarrah forest native legumes to fix nitrogen. Research Paper No. 21. Forest Department of Western Australia: Perth.) Squire, R.O. and Edgar, J.G. (1975). A study of natural regeneration of mixed eucalypts under partial cutting

45

D I S E A S E S

A N D

P A T H O G E N S

O F

conditions in the Wombat Forest. Research Branch Report 60. (Forests Commission of Victoria: Melbourne.) Squire, R.O., Dexter, B.D., Smith, R.B., Manderson, A.D. and Flynn, D.W. (1987). Evaluation of alternative silvicultural systems for Victoria’s commercially important mountain eucalypt forests. Project Brief: Working Draft. (Department of Conservation Forests and Lands, Victoria: Melbourne.) Stewart, H.T.L., Flynn, D.W. and Hopmans, P. (1985). On harvesting and site productivity in eucalypt forests. Search 16, 206–210. Stewart, H.T.L., Hopmans, P., Flynn, D.W. and Croatto, G. (1990). Harvesting effects on phosphorus availability in a mixed eucalypt forest ecosystem in south eastern Australia. Forest Ecology and Management 36, 149–162. Turner, J. and Lambert, M.J. (1986). Effects of forest harvesting nutrient removals on soil nutrient reserves. Oecologia 70, 140–148.

46

E U C A L Y P T S

Walters, M. (1991). The regeneration of Eucalyptus regnans F. Muell. under alternative silvicultural systems. 1. Seedling establishment and early height growth (First seasonal replicate). Silvicultural Systems Project Internal Progress Report 2. (Department of Conservation and Environment, Victoria: Melbourne.) Webb, D.P., Ellis, R.C. and Hallam, P.M. (1983). Growth check of E. delegatensis regeneration at high altitudes in north-eastern Tasmania. Canadian Forest Service Information Report 0-X-348. (Reprinted as CSIRO Division of Forest Research Reprint No. 370, Canberra.) White, B.J. (1971). Karri Silvics. Research Note No. 1. (Forest Department of Western Australia: Perth.) Wilson, N.W. (1993). Distribution of raw eucalypt seed by a helicopter-mounted sowing system. Forest Technical Report No. 11. (Department of Conservation and Natural Resources, Victoria: Melbourne.)

C H A P T E R

E COLOGY

OF

E UCALYPT R EGENERATION

4

D.H. Ashton

S

U M M A R Y

The eucalypts dominate the vegetation of Australia over a wide climatic range. The most important aspects of their persistence at a particular site are their longevity and their ability to regenerate. Drought and fire are the most important factors affecting eucalypts through most of their range, but insect and fungal attack is persistent and can impair survival and competitive ability of the species. Longevity is affected by various factors, including fire and various diseases of mature trees (root rot caused by Phytophthora cinnamomi, woody root rot caused by Armillaria species, stem and butt rots, infection by foliar parasites and mistletoe) but the most critical aspect is the seedling phase which is very susceptible to damage by abiotic (heat, desiccation, flooding, frost) and biotic factors, including damping-off and a range of foliar diseases. The conditions required for regeneration are reviewed and the main modes of regeneration are discussed in relation to the degree of stress of various environments. Finally, the strategies of survival of the eucalypts in the often harsh Australian environment are discussed.

47

D I S E A S E S

A N D

P A T H O G E N S

O F

4.1 Introduction The eucalypt genera Eucalyptus and Corymbia span the continent and dominate communities from the fringe of the north-east rainforests to the fringe of the central desert and the altitudinal tree line at about 1900 metres in the south-east (Fig. 4.1). The environmental range is thus enormous. Mean annual rainfalls range from less than 200 millimetres to more than 2000 millimetres with coefficients of variation from 15% to 80% and seasonal distribution from uniform to summer or winter types. Temperatures range from consistently hot to widely fluctuating or to cool with snowy winters. In the south-east they form the tree line at about 2000 metres. Soils are generally poor but range from nutrient-rich loams to very poor sands and laterites. There is a tendency for species of Eucalyptus subgenus Symphyomyrtus to occur on better soils and those of Eucalyptus subgenus Monocalyptus and genus Corymbia to occur on poorer soils (Florence 1996), although there are many exceptions and, in addition, ecotypic variation may be found in response to such edaphic factors.

E U C A L Y P T S

include dieback caused by Phytophthora cinnamomi Rands (see Chapter 11), woody root rots caused by Armillaria species (see Chapter 12) and stem and butt rots caused by a wide range of Basidiomycota (see Chapter 13). The incursion of mistletoes into disturbed vegetation particularly may also affect longevity of trees (see Chapter 15).

The stature of fully grown eucalypts ranges from diminutive shrubs, barely one metre high in the most extreme environments, to the tallest known angiosperms with heights at maturity in excess of 100 metres. A simplified scheme of certain key species in relation to an environmental fabric is shown in Figure 4.2. Eucalypts often form monocultures in either stressful or very favourable sites (see section 4.4) and form mixtures of from two to five species, often from more than one subgenus, in moderate sites. In relatively severe sites other genera may be present or even codominate the stands (e.g. Brachychiton, Callitris, Codonocarpus), whereas in some of the better sites, species of Allocasuarina, Lophostemon, Syncarpia and certain species of Acacia may be subdominant.

The regeneration niche is thus diverse, yet one factor, namely fire, is an important common denominator. Fires may occur whenever heavy fuel accumulation and dry weather coincide. Fire frequency increases to a maximum in the subhumid to semiarid zones; the wet forests only burn during extremely dry weather, and the desert vegetations only burn after periods of extremely wet weather that have promoted a lot of growth. South of latitude 25° south, the centrifugal hot dry winds emanating from the central desert may be associated with severe crown fires in the arc from Brisbane to Perth except for the whole Nullarbor region. In Tasmania, humus fires occur in some forests with devastating results (Cremer 1962). In wet forests in Victoria, heavy litter at the bases of old trees allows fire to burn for long enough to ‘ringbark’ or butt scar the tree. Butt scars are a common infection site for butt rot fungi (see Chapter 13). In this broad spectrum of habitat, eucalypt regeneration may be reliable or erratic and result in even-aged stands or groups in gaps between tree canopies. In unfavourable habitats, seedlings rapidly develop resistant, partly buried lignotubers. Suppressed lignotuberous regrowth (< 1–2 m tall), however, may occur beneath the overstorey as ‘advanced regrowth’ (Jacobs 1955). Such plants, once established, may persist through recurrent stresses for many decades and take advantage of any opening of the canopy. Most eucalypts have a capacity for copious epicormic growth provided fires are not so severe or frequent as to overcome the insulation provided by the bark.

The persistence of eucalypts on a site is a product of both the longevity of individuals and their regeneration. The latter is undoubtedly the more important aspect of their ecology. The seedling is the most vulnerable stage of growth and is frequently susceptible to drought, frost, overheating of surface soil, browsing, insect attack and, most importantly, fungal diseases (see Chapters 8 and 9). However, later growth stages are prone to a wide range of diseases that affect the longevity of trees. These

Biotic factors may affect the success of eucalypts on a particular site directly by predation, herbivory (Burdon and Chilvers 1974; Morrow 1976) or disease, or indirectly through competition among themselves or their understorey associates at particular stages. Generally in typical years, physical factors of the environment are likely to be more important in drier or more exposed sites, whereas biotic factors, including disease, are likely to be more important in wetter and more favourable sites.

48

E COLOGY

Figure 4.1

OF

E UCA LY PT R E GENE RA TION

C H A P T E R

4

Extent of eucalypt-dominated communities in Australia.

CLIMATE HOT

WARM

porrecta jacobsiana

macrorhyncha siderophloia

SOIL tetrodonta miniata

Figure 4.2

radiata obliqua

30 m pauciflora

60m

pilularis microcorys

regnans 90m

grandis

viminalis

bleeseri WET

COOL

oleosa incrassata

DRY

MOIST

MILD

delegatensis stellulata camphora

ovata camaldulensis

Isolines of eucalypt tree height in relation to some environmental parameters, indicating the occurrence of particular eucalypt species in relation to these factors.

49

D I S E A S E S

A N D

P A T H O G E N S

O F

4.2 Characteristics of eucalypts in relation to their regeneration 4.2.1

Seed

Most eucalypts have small seed (1–2 mm long) with oil storage in the cotyledons. Seed is produced at regular or irregular intervals depending on both the species and climate. Often it is stored in woody capsules, 5 to 30 millimetres in diameter, and held on the tree for several years, thus buffering variations in yearly production. On the tree, seed is consumed by minute beetles or various psittacine birds, and may suffer some loss from fungal infection (see Chapter 7). On the soil, seed is an important food source for insects such as ants and lygaeid bugs (Euander spp., Dieuches spp.) which avidly collect it on the soil or litter surface in most areas of the continent. In good years, seed is shed in enormous numbers, particularly following fires when seed fall exceeds the needs of consumers. Soilborne fungi may also take a toll of fallen seed, particularly on wetter sites.

4.2.2

Seedlings

With eucalypt seed being so small, the pre-emergence and postemergence seedling stage is very susceptible to damping-off in native forests (Mwanza and Kellas 1987) (see Chapter 8). Heavy loss of seedlings can occur at this stage, especially during cool, wet weather. Eucalypts are heteroblastic and the juvenile stages are usually characterised as having opposite dorsiventral leaves for three to five or as many as 30 to 40 pairs or more. The adult form is isobilateral in the Eucalyptus subgenera Monocalyptus and Symphyomyrtus (except E. botryoides and related species) but dorsiventral in Corymbia. Certain species have developed chemical defences in juvenile foliage (e.g. toxins such as cytogenetic glucosides) as a deterrent against insect attack and mammal predation (Pryor 1976). Some glaucous leaves have chemical defences against fungal attack (Heather 1967). Several leaf pathogens [e.g. Mycosphaerella nubilosa (Cooke) Hansf.] are confined to juvenile foliage; others are more common on juvenile than on adult foliage (see Chapter 9). Lignotuber development occurs in most species and commences as woody swellings in the lowermost leaf axils. These fuse and grow down into the soil where they provide a store of buds and carbohydrate

50

E U C A L Y P T S

protected from fires and browsing (Carrodus and Blake 1970). The largest lignotubers, recorded by Mullette (1978) from C. gummifera, formed a complex of 75 square metres. In some cases they have been attributed wrongly to galling caused by Agrobacterium tumefaciens (Smith & Townsend 1907) Conn 1942 (see Chapter 14). In some species, rhizomes (Lacey 1974) or ‘rhizostolons’ (Gillison et al. 1980) develop from these organs and emerge to produce new regrowth one or more metres from the parent. In most of the species that dominate the tall wet forests (wet sclerophyll or tall open forest), lignotubers are not developed and their capacity for vegetative regeneration after damage is meagre.

4.2.3

Tree form

The trunk of the tree varies conspicuously in the type and thickness of bark. In more fire-prone areas, bark is thick and is liberally endowed with dormant buds that sprout as epicormic shoots after fire. Bark thickness increases with stem diameter and is therefore thicker at the butt where the impact of fire is greatest. However, coppice from butts may occur even in some species without lignotubers. Litter is flammable and slow to decay in all but the humid environments, thus accumulating and encouraging fire. The oil content in glands in the foliage is often high especially in Monocalyptus species (e.g. 3% by weight in E. dives; Ewart 1930), producing explosive conditions in crown fires. The great height of trees in the wet climates ensures canopy survival from surface fires, but the sheer biomass of such forest ensures cataclysmic fires when conditions are severe. While fire is the most important factor in most of the Australian eucalyptdominated communities, a point emphasised succinctly by Gill (1975), insect and fungal attack of foliage is persistent in eucalypts and can seriously impair survival of regeneration or its competitive ability in the presence of species not so attacked. In general, gall insects attack expanding leaves, chewing and sap sucking insects attack the current year’s leaves and fungal disease is most evident on older leaves. Although fungi may seriously attack young leaves, the severity of fungal leaf spots becomes progressively greater on two-year-old and three-year-old leaves. Damping-off is common among dense seedling regeneration and foliar diseases can be destructive in seedlings in the first year or two (see Chapter 8). While fungal diseases of foliage are common in native forests, they are

E COLOGY

not usually destructive (see Chapter 9). However, alteration of the forest environment could lead to epidemics.

adequate seed supply following adequate conditions for flowering and seed set

2

sufficient quantities of seed to allow satiation of seed harvesting insects

3

favourable microflora and (premycorrhizal) rhizosphere associations.

Germination conditions: 1

a favourable seedbed, especially bare soil free of litter and ground stratum (grasses, ferns, shrubs)

2

maintenance of suitable conditions of soil moisture and temperature

3

slight burial which reduces predation by seedharvesting insects (ants, lygaeid bugs).

C H A P T E R

4

adequate light to allow development through the juvenile stages of lignotuber production

8

sufficient growth to allow seedlings to endure the stress period of the following season such as seasonal drought, frost, flood inundation or snow cover

9

sufficient light and freedom from root competition, usually as a result of larger canopy gaps, to enable development through the sapling and pole stages to the adult stage.

Seed supply: 1

E UCA LY PT R E GENE RA TION

7

4.3 Conditions required for regeneration The ideal conditions required for regeneration (germination to adult seed-bearing stage) of eucalypts are as follows.

OF

4.4 Major modes of regeneration In general the major modes of regeneration are related to climate and the adaptation of the species to the important limiting factors in their environment. The attributes of eucalypts over their climatic range in Australia (Fig. 4.3) as they relate to their modes of regeneration are discussed below. Because of their considerable variability, many eucalypt species may range over more than one habitat type. The climatic range of eucalyptdominated communities and their associated opportunities for regeneration can be categorised as follows: 1

stressful sites (scrub, semiarid woodland, semiarid mallee, many subalpine woodlands, coastal heath)—seedling regeneration rare or erratic

Seedling development: 1

one or more favourable seasons following germination

2

2

early protection from exposure to heat, frost and desiccation, and from rain splash which may carry pathogens (see Chapter 9, especially in relation to winter leaf spot of E. regnans caused by Piggotia substellata Cooke and Ceuthospora innumera Massee)

hazardous sites (woodlands)—seedling regeneration occasional and often at long intervals; vegetative spread possible in tropical regions

3

floodplain sites (open forest to woodland)— regeneration by seed under the control of regular or erratic flood regimes

4

reliable sites (open forest; subhumid to humid; climate relatively favourable for plant growth)— regeneration common especially following fires

5

very favourable, high forest sites (tall open forest; humid to very humid; site conditions very favourable for plant growth)—opportunities for regeneration are infrequent and controlled by disturbances such as fire and wind throw.

3

soil conditions that allow rapid root penetration

4

sufficient air movement and low humidity to reduce damping-off and other diseases (see Chapter 8)

5

low incidence of insect predation of seedling buds and foliage

6

protection from browsing marsupials, including sufficient alternative feed, or sufficient numbers of gaps between seedlings to allow dispersion of browsing and survival of at least some seedlings

4.4.1

Stressful sites

Stressful sites occur in wind-swept coastal or subalpine or regularly drought-prone areas. In these

51

D I S E A S E S

A N D

250

P A T H O G E N S

O F

500

E U C A L Y P T S

750

1000

1250 mm

Stature

Regeneration

Understorey

Lignotuber

Figure 4.3

Stature, regeneration, understoreys and lignotuber development in eucalypts with increasing mean annual rainfall.

sites, eucalypts are low growing (1–8 m) and open spaces between them are large (Plate 4.1). They characteristically have large, conspicuous lignotubers that project above ground and support several stems of equal dominance. They are often gnarled in old age. Regeneration is rare and follows extremely favourable seasons and combinations of seasons. In the semiarid mallee of Victoria, seeds germinate in the winter and spring when they are frost prone. In the first summer they are drought prone (Parsons 1969; Wellington and Noble 1985). High root to shoot ratios in the seedling stages of different species or ecotypes are considered by Parsons (1994) to be an important attribute in successful establishment. After fire, seedlings occur in densities of up to 900 per square metre in hollows where wind and water have collected seed and charred debris. Under these

52

conditions the partitioning of moisture resources may be insufficient to allow seedlings to withstand the first summer droughts (Wellington and Noble 1985; Wellington 1989). If they survive and produce lignotubers they will be virtually indestructible and may live for many hundreds of years. Because eucalypts are ‘crown shy’ due to their system of naked buds (Jacobs 1955), stems arising from the lignotuber grow outwards causing increased strain. If the original stem dies, a lignotuberous ring results (Fig. 4.4). Death of the stem may occur when the moment of torque exceeds the strength of the roots, and the rings segments are uprooted. Infection by wood rot fungi such as Phellinus rimosus (Berk.) Pilát (see Chapter 13) may also occur on the exposed upper sides of leaning stems where thin bark may not protect the cambium from damage inflicted by excessive sun scorch.

E COLOGY

Figure 4.4

OF

E UCA LY PT R E GENE RA TION

C H A P T E R

4

Stressful site: Eucalyptus behriana mallee, showing hollow left by the decay of the lignotuber, Melton, Vic.

In the subalpine zone at 1500 to 1800 metres, E. pauciflora develops patches of suppressed growth, each with their own lignotuberous rings. Here, regeneration is limited by snow lie and frost and by severe desiccating winds in winter and spring (Jacobs 1955; Costin et al. 1964; Farrell and Ashton 1973; Ashton and Hargreaves 1983; Ashton and Williams 1989). In snow gum woodlands, regeneration is also dictated by the density of the fine grass tussocks of Poa hiemata Vickery and others of this complex (Plate 4.1). Whereas the seedlings appear to need gaps for establishment they also need the protection of the overhanging grass tussocks against frost. In open situations (e.g. Mt Wellington plains, North Central Gippsland, Vic.), regeneration is commonly restricted to microsites beneath the eucalypt canopy. Suppressed growth is common under the canopy in wetter areas of these forests and woodlands. In some places, snow gums may be killed by fire if humus soils burn and kill the relatively superficial lignotuber (Jacobs 1955). In coastal heaths on deep sands, eucalypts may also develop a mallee form and regeneration is largely prevented by the dense, fire-resistant heath species [e.g. in Victoria Leptospermum myrsinoides Schldtl.

and Allocasuarina pusilla (Macklin) L.A.S. Johnson]. Occasional eucalypts (E. baxteri, E. obliqua) may remain suppressed for many years before emerging above the heath stratum at two metres. Once this occurs, the eucalypts inhibit the heath dominants and form a modified sclerophyll forest or woodland.

4.4.2

Hazardous sites

These occur in subhumid areas with a long severe dry period, annually or lasting many years. Eucalypts in these sites have been shown to regenerate by two modes—seed or rhizomes and root suckers. In tropical areas, several species (C. jacobsiana, C. porrecta) develop dense clones from shallow rhizostolons after fire. Such plants later thin out to form woodland (Lacey 1974) (Plate 4.2). However, in temperate zones, rhizostolons are relatively rare (Gillison et al. 1980). These communities vary considerably in density and size—they are commonly between 10 and 30 metres tall. Gillison (1996) has pointed out the great physionomic variation of woodlands, including monopodial, sympodial and hemisympodial forms. The environments are often unfavourable for seedling establishment, and hence stands may become increasingly open with age until

53

D I S E A S E S

Figure 4.5

A N D

P A T H O G E N S

O F

Floodplain: seed of Eucalyptus camaldulensis (see arrows) shed on flood deposit in late spring, Tocumwal, NSW.

the right sequence of years enables regeneration to occur. This may be sporadic and scattered, perpetuating the woodland structure, or may result in much denser patches of vegetation with an almost open forest form in the early stages of tree development. Thus, grassy woodlands in the Australian Capital Territory have regenerated only at long intervals, when sequences of three wet years have occurred. According to Jacobs (1955, p. 216) it takes three years to establish the lignotuberous seedling of such tree species. Frequently, regeneration is conspicuously inhibited by the presence of the tree crown and groups occur beyond this up to the distance of seed throw as an asymmetric halo, commonly extending for a distance of from one to three tree heights down wind or down slope. In the tropics (e.g. Arnhem Land), one of the major species, E. tetrodonta, has the capacity to regenerate from root suckers when the stand is damaged or soil is disturbed (Plate 4.3). If cleared or felled by cyclones after being weakened by termite attack, E. tetrodonta can replace its population by this means and grow to 3.8 metres in two seasons. The intact stand up to 24 metres tall may consist of 310 trees per hectare, of which only a very small

54

E U C A L Y P T S

percentage are less than two metres tall; the paucity of shrub regrowth in these forests is probably due to annual or biennial fires and the density of tall annual Sorghum, which itself is promoted by repeated late season fires. In many sites, eucalypts are facultatively deciduous (Plate 4.4).

4.4.3

Floodplain sites

The open forests and woodlands on these sites are epitomised by E. camaldulensis and to a lesser extent E. largiflorens in the Murray River central tract where the moderately low rainfall (300–350 mm per annum) is supplemented to various extents by flooding (Plate 4.5). Floods from the melting of the alpine snows are erratic, occurring every one to five or 15 years depending on the distance from the river and the height of the floodplain above the river. There is thus a gradation of site quality from too little to too much flooding. Trees vary in size and density and mature heights range from 20 to 42 metres. In the best site quality, one to two centimetres of silt is deposited annually and regeneration occurs from seed fall onto this silt (Fig. 4.5). In this site, about 200 trees per hectare are 12 to 30 metres tall and occur above

E COLOGY

regrowth with a density of 360 trees per hectare. In the poorer, more open sites, trees are 12 to 24 metres tall with a density of 100 to 120 trees per hectare. Regeneration following very high floods occurs in these sites and is restricted to positions between the tree crowns. Regeneration follows seed fall at the time of floods (Jacobs 1955) (Plate 4.6). Seed washed or blown to the edge of the flood germinates densely in the worst sites. Seed dropped among flood debris frequently is successful due to the protection offered from surface evaporation. Germination among the grass sedge sward of the intermediate site qualities is disadvantaged by dense root competition. Seed may be washed or blown over the water surface to the edge of the flood. If the flood is extensive, germinants are often stranded in the most unfavourable sites and therefore rarely survive. The best growth of E. camaldulensis occurs where floods occur every two years to three years, thus ensuring a regular replenishment of water reserves and a top dressing of one to two centimetres of fine silt. Regeneration follows floods, soil disturbance or surface fires and in such sites seedlings produce deep root systems which reach watertables in aerated gravel and sand layers (Jacobs 1955). In this way they are sturdy or tall enough to withstand any inundation of the next flood. Weak seedlings inundated for more than three months are seriously affected or killed, or unable to withstand the weight of deposited floating hydrophytes (Azolla and Lemna) following flood recession. Very frequent and prolonged flooding, however, is deleterious to E. camaldulensis and forest is replaced by rampant grasslands (Chesterfield 1986). The behaviour and regeneration of these communities is, therefore, under the control of flood frequency and intensity—without such water supply, gaps may remain unfilled for 15 years or more (Dexter 1978).

4.4.4

Reliable sites

The type of regeneration on these sites is relatively reliable—climatic conditions are adequate in most years and fire frequency is sufficient to permit regeneration to occur in gaps and persist as advanced lignotuberous regrowth one to two metres tall. Seed harvesting by ants is rife. Therefore, establishment usually occurs after fire, when seed fall is greatly in excess of demand, and when transpiration stresses are reduced, soil nutrients more available and light intensity increased during the period of crown repair.

OF

E UCA LY PT R E GENE RA TION

C H A P T E R

4

Advance regrowth is a most important aspect of the forest regeneration cycle which takes advantage of the favourable opportunity for establishment and persists until the appropriate canopy-space becomes available. In E. marginata forests of south-west Western Australia, this understorey of arrested development can quickly grow as a group of ‘evenaged’ saplings and trees when old trees die or are wind thrown (Plate 4.7) (van Noort 1960). The depth of the watertable is of critical importance for survival in this forest. In analogous forests of E. obliqua and E. radiata in central Victoria such regrowth, predominantly of E. radiata, also occurs (Gill and Ashton 1971). Such forest mixtures may show oscillation of dominance if fire does not allow the restoration of E. obliqua regeneration. In somewhat drier environments, soil type may discriminate between overstorey eucalypts and type of understorey. Thus, on poor soils sclerophyll shrubs are predominant (Plate 4.8) but on richer soils these are replaced by graminoids and forbs (Plate 4.11). In Victoria, some low open forests and woodlands of E. macrorhyncha and E. dives may develop a diffuse stratum of suppressed regeneration consisting mainly of E. dives. Such forests appear to be unstable mixtures and given the continuing progress to maturity, this regeneration may assert itself to produce a forest overstorey of changed composition, possibly maintained by the effect of host-specific pathogens (see Chapter 9). The differential success of such regeneration could be the result of relative seed availability at the time of the last fire, the relative ecological tolerance of the species to drought and shade imposed by the overstorey and understorey, and their relative resistance to insect and fungal attack. In these cases, the more ‘tolerant’ species tend to be those in which the dorsiventral, horizontal juvenile foliage persists for a long time. In mixed stands of dry sclerophyll forest at Mallacoota, Vic., C. gummifera and E. botryoides with dorsiventral foliage are conspicuous as a suppressed stratum one to three metres high beneath an overstorey of C. gummifera, E. botryoides, E. globoidea and E. sieberi. Eucalyptus botryoides was severely attacked by the psyllid, Cardiaspina bilobata Taylor, in the 1980s and 1990s and this in the long term may substantially alter the outcome of stand competition. Following the severe fires at Mt Macedon, Vic., in 1983, E. obliqua regenerated prolifically both under

55

D I S E A S E S

A N D

P A T H O G E N S

O F

tree canopy and in gaps. After three years all seedlings were severely attacked by the leaf spotting fungus, Aulographina eucalypti (Cooke & Massee) Arx & E.Müll. (see Chapter 9). Only in the better quality microsites were seedlings able to outgrow these attacks and survive. Under the regenerated tree canopy 10 years after the fire, the demise of all seedling regeneration was undoubtedly hastened by severe leaf spot damage, so that after 15 years, regeneration only survived in overstorey gaps.

4.4.5

Very favourable, tall forest sites

In these forests, the site of most current timber and pulpwood extraction from native forests in Australia, the canopy may be 50 to 100 metres tall with an understorey of dense shrubs, trees, tree ferns, ground ferns and tussock or scrambling grasses (Plates 4.9, 4.10, 4.12 and 4.13). The dense understorey is the primary barrier to regeneration of the eucalypts. The shade tolerance qualities and the density of understorey is enhanced when long absence of fire encourages rainforest elements to establish where they are within dispersal range. Large gaps in the overstorey may be caused by multiple tree falls, or patches of sustained attack in certain areas by lerps or stick insects [Didymuria violescens (Leach)]. Such gaps may be regenerated if the understorey senesces or is temporarily removed by fire. Thus, two or three age classes can occur in some forests although many are even-aged as a result of widespread severe fires. In Tasmania, Bowman and Kirkpatrick (1984) have indicated that many of the tall open forests and tall woodlands of E. delegatensis are multiaged as a result of light fires. Although in Victoria many of the forests of this species are even-aged as a result of very severe wildfires (Grose 1963), regeneration does occur without the intervention of fire in light or senescent understoreys where trees are widely spaced with woodland form. Such tall woodlands may indicate long periods of regeneration difficulty in upper montane sites and be analogous to those situations described previously for hazardous sites. In large, well-lit areas of bracken (one to many hectares) created by recurrent overlapping fires, colonisation by E. regnans and understorey species from surrounding forest can occur without fire provided that the bracken community has developed patchiness of vigour on a microscale, sensu Watt (1955).

56

E U C A L Y P T S

In general, where rainfall is high enough (> 1500 mm/annum) and the probability of severe fires sufficiently low in eastern Australia, tall open forest eucalypts clearly occupy potential rainforest sites (Plates 4.9, 4.10 and 4.12) (Jackson 1968; Ashton and Attiwill 1994). Most of the fast-growing, tall eucalypts of these wet climates are non-lignotuberous and depend upon the enrichment of the ash-bed soil after fire to realise their full height. Under conditions of full light, high soil moisture storage and adequate nutrients they outstrip the understorey associates in one to two years. Under the canopy of the mature trees, however, the success of regeneration is much less assured. If initiated by surface fires, regeneration may be sufficiently stimulated to compete with the understorey and then remain suppressed as saplings of 10 to 20 metres tall for 30 to 40 years until killed by rare periods of drought. Without fire, chance regeneration on bared soil may survive the juvenile stages, only to succumb to understorey competition within five to 10 years. Survival beyond the juvenile stage is particularly hazardous because of attack by insects and damping-off fungi, and browsing by wallabies or possums. Lethal winter leaf spot disease, spread from litter, destroys all but the earliest of the season’s germination of E. regnans in the forest environment (Ashton and Macauley 1972) (see Chapter 9). In the humid microclimate of the mature forest, damping-off of tender cotyledonary seedlings by fungi such as Alternaria may be very common under shady conditions in wet summers. At higher elevations, snow damage and water infiltration as well as leaf and shoot blight caused by Botrytis cinerea Pers. occurs in E. delegatensis when regeneration is insufficiently robust (Grose 1963). In this case, regeneration on warmer slopes and on ashbeds is sufficiently vigorous to survive the critical early years. Seed losses from harvesting ants and lygaeid bugs may account for 60% to 90% of the year’s seed fall of E. regnans (Cunningham 1960; Ashton 1979). Germination may be delayed by overheating of the exposed soil surface; if delayed until autumn in a forest environment, the hazards of winter survival become real. In the montane E. delegatensis forests, seed is dormant because of the necessity for stratification. Hence, germination is delayed until the following spring and thus avoids the lethal frosting of winter. Under regimes of even-aged regeneration, fires in summer kill forest

E COLOGY

over very large areas and establishment of seedlings follows autumn rains. Under these open conditions, hazards of season and of fungal attack are minimised. In south-west Western Australia, the tall forests of E. diversicolor have a similar ecology and the remarkably similar form of the understorey imposes similar restraints (Plate 4.13). Where mixtures with the slower growing, more fire-resistant and lignotuberous C. calophylla occur in this region an unstable mixture is evident (Christensen 1972). Arrested lignotuberous regrowth of C. calophylla may occur commonly in the understorey where, due to its greater shade tolerance, it persists for long periods until an opportunity arises for it to develop further. Without fire for very long periods this species would probably become dominant. The intervention of fire at a time when E. diversicolor is bearing abundant seed would certainly restore dominance of this species. In some of the wettest forest in this region, tall mature E. diversicolor and very large, ancient E. guilfoylei and E. jacksonii occur with a tall second stratum of Allocasuarina decussata (Benth.) L.A.S.Johnson (20–40 m) which shows a wide range of girth classes. One interpretation is that, in the absence of true rainforest, this species may finally dominate the site in the event of a very long absence of fire. However, it could be argued that relatively high fire frequency is endemic to this region (Underwood 1978; WardellJohnson and Coates 1996) and that regeneration of eucalypt forest in some form is assured. In south-east Australia, a similar interpretation could be made of some old E. regnans forests in moderately wet climates where large Acacia melanoxylon R.Br. (30–45 m) forms the second stratum in the absence of rainforest elements. In such instances, a long period of fire absence in excess of 400 to 500 years may allow a complex temperate forest to be dominated by this species and the understorey species, Olearia argophylla (Labill.) Benth. An analogous situation occurs on the Atherton Tableland in North Queensland where wet sclerophyll forest of E. grandis is zoned between rainforest and grassy forest dominated by C. intermedia. Eucalyptus grandis, like E. diversicolor and E. regnans, is both nonlignotuberous and fast growing and is not particularly fire resistant, especially in the young stages. Corymbia intermedia, a bloodwood like

OF

E UCA LY PT R E GENE RA TION

C H A P T E R

4

C. calophylla, is large seeded and relatively slow growing, develops a strong lignotuber and is fire resistant. It can thus withstand fire early in its life and can persist in the presence of tall grasses such as Themeda triandra Forssk. and Imperata cylindrica (L.) P.Beauv. Fires tend to weaken and die out at the rainforest margin. In this niche, E. grandis can assert its height growth superiority and dominate the rainforest elements, for a time. It cannot survive the fire intensity or competition in the sites further away from the rainforest ecotone, although the environment is otherwise suitable (Unwin 1989). The lack of vigour of some eucalypt seedlings in unburnt mature forest of E. regnans or E. pilularis suggests that some antagonistic factors are present. Ellis and Pennington (1992), in studying dieback of E. delegatensis in Tasmania, suggested that these factors may include the age of the dense understorey, a dense grass stratum or the humus type and perhaps the cool microclimate of the root zone. In mature E. pilularis forest soil, Florence and Crocker (1962) suggested that a microbiological antagonism may be the cause of seedling inhibition. This effect was alleviated by fire, heavy fertiliser application, or aeration and desiccation of the soil. In E. regnans forests, the poor growth of young seedlings on soils in unburnt, constantly moist microsites may be spectacularly stimulated by air drying the soil before planting. This results in increases in both available phosphorus and nitrogen and in changes in the microflora in the short term (Ashton and Kelliher 1996). Some effects may be due to exudates from the living root mat of mature E. regnans and Pomaderris aspera A.Cunn. ex DC. (Ashton 1962), to the allelopathic effects of soil lipids (Ashton and Willis 1982) or to the aqueous phase of essential oils from leaves. An interesting development has been the discovery that some strains of the rhizosphere fungus, Cylindrocarpon destructans (Zinssm.) Scholten (Evans et al. 1967), isolated from the roots of moribund E. pilularis seedlings from the mature forest, produce a phytotoxic substance (nectrolide). This fungus has been isolated also from the root surfaces of E. regnans seedlings from the mature forest. The antagonism towards seedlings of mature forest soils can be demonstrated in the glasshouse by growing E. regnans seedlings in freshly collected top soil. Seedlings are unthrifty and purplish. If soil is incubated for three months in warm to hot glasshouse conditions or merely air dried at 20°C to

57

D I S E A S E S

A N D

P A T H O G E N S

O F

45°C, plants are subsequently vigorous and healthy (Ashton and Kelliher 1996). The rhizosphere microflora from numerous root samples of green and purple seedlings was examined by Hin Yuen Yipp (pers. comm.) and results analysed by classificatory programs. Certain species were consistently associated with healthy plants and others with purple plants. The association of health of seedlings with groups of fungal species (and bacteria) suggested that Cylindrocarpon destructans may be an important species in this syndrome and that its effect may be mediated by the presence of other species. However, the appearance of inhibited E. regnans seedling root systems does not suggest damage by microorganisms. Seitz-filtered, aqueous culture medium of Cylindrocarpon destructans certainly caused the death of root tips in vitro (Ashton and Willis 1982), but in glasshouse experiments the effect of inoculation of this species into either sterile or nonsterile soil is neither as consistent as, nor as severe as, the inhibition evident in undried forest soil. Launonen (1995) subsequently demonstrated that although the effect occurred in sterile conditions, it was negated in unsterile soil possibly by the action of the microflora on the fungus. The desiccation of soil greatly increases the availability of phosphorus to seedlings (Ashton and Kelliher 1996 ) and may change the nature of the mycorrhizal relationships (Warcup 1983). R.J. Kelliher and D.H. Ashton (unpubl. data) have shown that although air drying of soil decimates the microbial populations, bacteria and fungal numbers (determined from soil dilution plates) rebound within two to three weeks to their original levels whereas recovery of actinomycete numbers is very slow. Some mycorrhizal fungi, particularly Ascomycota, survive such drying treatment and form symbiotic relationships in four to six weeks. The research into this facet of forest regeneration has only begun. It seems clear that the microflora can be modified by climatic conditions and the composition of the forest community and above all, as shown by Renbuss et al. (1973) and Chambers and Attiwill (1994), by the partial sterilisation wrought by heat and fire.

4.5 In synthesis—the strategies of survival Eucalypts are in general opportunists, producing abundant seed periodically. Their flammable foliage and litter and abundant production of fine, readily

58

E U C A L Y P T S

cast twigs aids the spread of fire. Most are fire resistant, and all are fire tolerant provided fire frequency does not encroach upon their sensitive non-flowering juvenile period nor their early