Contents

PREFACE vii

ACKNOWLEDGEMENTS ix

1 INTRODUCTION 1

2 HISTORY AND PRESENT STATE 5 OF TIMBERLINE RESEARCH

2.1 Early timberline research 5

2.2 Modern timberline research 7

3 DEFINITIONS, TERMINOLOGY 11

4 PHYSIOGNOMIC AND ECOLOGICAL 29 DIFFERENTIATION OF MOUNTAIN TIMBERLINE

4.1 Tree species at timberline 29

4.1.1 Influence of geological and floral history 29

4.1.2 Tree species at temperate and northern timberlines 32

4.1.3 Tree species at timberlines in the southern hemisphere 42 and in the tropics

4.2 Relationship of timberline elevation to macroclimate, 49 climate character, and the mass-elevation effect

4.3 Ecological conditions and processes at the timberlines 58

4.3.1 Heat deficiency 58

4.3.2 Carbon balance, carbon limitation 61

4.3.3 Frost tolerance and damage 65

4.3.3.1 Temperate and northern timberlines 65

4.3.3.2 Tropical timberlines 73

4.3.4 Winter desiccation and abrasion 75

4.3.5 Soil temperature 86

4.3.6 Wind 104

4.3.7 Snow cover 107

4.3.7.1 Distribution and characteristics of snow cover 108

4.3.7.2 Effects of the snow cover on sites 111

4.3.8 Soils 122

4.3.9 Topography/geomorphology 135

4.3.9.1 Slope gradient and geomorphic structure 136

4.3.9.2 Exposure 162

4.3.10 Regeneration 167

4.3.10.1 Seed-produced regeneration 167

4.3.10.2 Vegetative reproduction 182

4.3.11 Influence of site conditions on growth form 188

4.3.12 Influence of trees and tree stands on site conditions 220

4.3.13 Influence of animals on timberline 244

4.3.13.1 Large herbivorous mammals 245

4.3.13.2 Burrowing herbivorous mammals 253

4.3.13.3 Birds 254

4.3.13.4 Defoliating insects (Epirrita autumnata, 264 Operophtera brumata)

4.3.14 Anthropogenic impact on timberline 268

4.3.14.1 Lowering the timberline 268

4.3.14.2 After-effects of timberline decline and present 278 impact

5 TIMBERLINE FLUCTUATIONS 293

5.1 General aspects 293

5.2 Timberline fluctuations in the past 297

5.3 Driving processes and adverse factors controlling 299 present timberline dynamics

5.4 Regional variation in timberline response after the 301 'Little Ice Age'

5.5 Conclusions and perspectives 326

6 TIMBERLINE PROSPECTS AND RESEARCH 335 NEEDS

REFERENCES 343

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