Plant Ecology

Plant Ecology

Ernst-Detlef Schulze · Erwin Beck · Klaus Mçller-Hohenstein

Plant Ecology Ernst-Detlef Schulze · Erwin Beck · Klaus Mçller-Hohenstein

Plant Ecology

With 506 Figures, most of them in colour, and 101 Tables

1 2 Professor Dr. Ernst-Detlef Schulze Translated by:

Max-Planck-Institute for Biogeochemistry

P.O. Box 100164 Gudrun Lawlor, FIL

07701 Jena Dr. Kirsten Lawlor

Germany Dr. David Lawlor

9 Burywick

Professor Dr. Erwin Beck Harpenden

Department of Plant Physiology Hertfordshire

University of Bayreuth AL5 2AQ

95440 Bayreuth UK

Germany

Professor Dr. Klaus Mçller-Hohenstein

Department of Biogeography

University of Bayreuth

95440 Bayreuth

Germany

Original title:

Ernst-Detlef Schulze/Erwin Beck/Klaus Mçller-Hohenstein, Pflanzenækologie

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31/3150 5 4 3 2 1 0±Printedonacid-freepaper Preface

Content: This textbook starts at the level of the sociates and last, but not least, our families.

cell and molecular aspects of plant responses to Without the support and help of many collea-

the environment, which is never stress free. gues, friends and coworkers, it would not have

Building on this molecular ecophysiology, the been possible to finish this book in time so that

organisation and regulation of metabolism of it does not contain chapters which are outdated

whole plants will be described from an autecolo- before publication. Particular thanks are given

gical perspective. In the following parts, this to Mrs Barbara Lçhker, without whose thorough

book deals with the interactions with other or- editorial work this book probably would have

ganisms at the level of the ecosystem. Finally, never been completed. For the critical reading of

geographical and long-term conditions for the individual chapters, for advice and pointers to

expansion and dynamics of plant populations the literature, the authors would like to thank

and species on earth are discussed. The book many colleagues, in particular: A. Arneth (Jena),

closes with the element cycles on earth and thus K. Beierkuhnlein (Bayreuth), C.M.P. Blum (Ut-

stresses the influence of man on original, so- recht), H. Bohnert (Urbana), U. Deil (Freiburg),

called natural ecosystems. W.H.O. Ernst (Amsterdam), S. Fettig (Bayreuth),

As the book covers several different concep- E.Gloor(Jena),G.Guggenberger(Halle),F.Haakh

tual levels, many aspects and facts will be illu- (Stuttgart), U. Heber (Wçrzburg), H.W. Heldt

minated from very different viewpoints: the cell, (Gættingen), J. Kaplan (Jena), O. Kolle (Jena),

the plant, the ecosystem, the zones of distribu- U.Kçper (Bayreuth), O.L. Lange (Wçrzburg),

tion and earth as a whole. Thus, the authors W.Larcher (Innsbruck), C. Neûhæfer and G. Or-

have tried to fully consider the enormous width lich (Bayreuth), C. Ploetz (Wuppertal), M. Popp

and complexity of plant ecology. (Vienna), R. Voeseneck (Utrecht), R. Scheibe

The reader: The textbook is aimed at advanced (Osnabrçck), W. Schulze (Tçbingen), E. Steudle

students and their teachers. Knowledge in var- (Bayreuth), C. Wirth (Jena) and W. Zech and

ious disciplines of natural sciences is expected, P.Ziegler (Bayreuth).

from molecular biology to the earth sciences. Special thanks are also extended to Springer-

The authors have tried to recommend textbooks Verlag for having translated the original German

and articles from the relevant literature in each book published by Spektrum Akademischer Ver-

chapter. This ªfurther readingº is intended to lag. Both publishers obliged most of the requests

deepen the relevant knowledge and to help de- by the authors in a constructive manner and re-

velop an understanding in relation to neighbour- spected the individuality of the authors, even

ing fields. Additionally, basic knowledge is revis- though they had to consider the homogeneity of

ited in concise box-type texts. Conceptual the final product.

knowledge is abstracted and strengthened in ex- The authors hope for a good reception of

tensive summaries at the end of each section. Plant Ecology by interested readers and welcome

Thanks: Writing this textbook has been a plea- constructive criticism in the knowledge that the

sure, but has also cost the authors much of the writing of a textbook about plant ecology in its

one commodity which they lack most: time. A entirety is an almost insurmountable task.

great deal of what could and should have been

done was left by the wayside. We therefore ask E.-Detlef Schulze, Erwin Beck and

all those whom we did not give enough of our Klaus Mçller-Hohenstein

time to make allowances, in particular our as- Bayreuth and Jena, October 2004 Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . 1 1.5 Water Deficiency (Drought) . . 117

1.5.1 Water Balance of Drought-Stressed

Chapter 1 Cells . . . . . . . . . . . . . . . . . . . . . . . . 119

Stress Physiology . . . . . . . . . . . . . . . . . 5 1.5.2 Cellular Reactions to Drought Stress 123

1.5.3 CAM

(Crassulacean Acid Metabolism) . . . 135

1.1 Environment as Stress Factor:

1.5.4 Anatomical-Morphological Adapta-

Stress Physiology of Plants . . 7 tion to Drought . . . . . . . . . . . . . . . . 140

1.1.1 Abiotic and Biotic Environments

Cause Stress . . . . . . . . . . . . . . . . . . 7 1.6 Salt Stress (Osmotic Stress) . . 145

1.1.2 Specific and Unspecific Reactions

1.6.1 Physiological Effects of Salt Stress

to Stress . . . . . . . . . . . . . . . . . . . . . 9

(NaCl) . . . . . . . . . . . . . . . . . . . . . . . 146

1.1.3 Stress Concepts . . . . . . . . . . . . . . . . 11

1.6.2 Adaptive Responses of Plant Cells

1.1.4 Perception of Stress and Creation

to Salt Stress . . . . . . . . . . . . . . . . . . 149

of Signals . . . . . . . . . . . . . . . . . . . . 13

1.6.3 Avoidance of Salt Stress . . . . . . . . . 171

1.1.5 How to Measure Stress on Plants? . . 16

1.1.6 Production of Stress-Tolerant Plants

1.7 Heavy Metals . . . . . . . . . . . . . . . 175

by Genetic Engineering? . . . . . . . . . 16

1.7.1 Availability of Heavy Metals . . . . . . 176

1.1.7 Gene Silencing . . . . . . . . . . . . . . . . 19

1.7.2 Heavy Metal Deficiency ± Example

Iron . . . . . . . . . . . . . . . . . . . . . . . . . 176

1.2 Light . . . . . . . . . . . . . . . . . . . . . . . 23 1.7.3 Stress by Heavy Metal Ion Toxicity . 182

1.2.1 Visible Light . . . . . . . . . . . . . . . . . . 24 1.7.4 Reaction of Plants to Excess Supply

1.2.2 UV Radiation . . . . . . . . . . . . . . . . . 37 of Heavy Metals . . . . . . . . . . . . . . . . 184

1.7.5 Heavy Metal Resistance (Tolerance) 191

1.3 Temperature . . . . . . . . . . . . . . . . 45 1.7.6 Heavy Metal Extraction and Soil

1.3.1 Temperature Ranges and Tempera- Decontamination by Plants

tures Limiting Life . . . . . . . . . . . . . . 45 (Phytomining, Phytoremediation) . . 191

1.3.2 Temperature-Dependent Biochemical

Processes, Q and Activation Energy 48 1.8 Aluminium . . . . . . . . . . . . . . . . . 195

10

1.3.3 Temperature and Stability/Function 1.8.1 Forms of Aluminium Available to

of Biomembranes . . . . . . . . . . . . . . 49 Plants . . . . . . . . . . . . . . . . . . . . . . . 196

1.3.4 Heat (Hyperthermy) . . . . . . . . . . . . 50 1.8.2 Aluminium Toxicity . . . . . . . . . . . . 196

1.3.5 Cold . . . . . . . . . . . . . . . . . . . . . . . . 61 1.8.3 Al3+ Resistance . . . . . . . . . . . . . . . . 200

1.3.6 Frost . . . . . . . . . . . . . . . . . . . . . . . . 72 1.8.4 Al3+ Tolerance . . . . . . . . . . . . . . . . . 203

1.3.7 Concluding Comments . . . . . . . . . . 94

1.9 Xenobiotica . . . . . . . . . . . . . . . . . 207

1.4 Oxygen Deficiency 1.9.1 Herbicides . . . . . . . . . . . . . . . . . . . . 210

(Anaerobiosis and Hypoxia) . . 99 1.9.2 Gaseous Air Pollutants . . . . . . . . . . 215

1.4.1 Energy Metabolism of Plants Lacking

Oxygen . . . . . . . . . . . . . . . . . . . . . . 101

1.4.2 Anatomical-Morphological Changes

During Hypoxia . . . . . . . . . . . . . . . 105

1.4.3 Post-anoxic Stress . . . . . . . . . . . . . . 114 VIII Contents

1.10 Biotic Stress: Herbivory, 3.2 Processes in Stands and

Infection, Allelopathy . . . . . . . 235 Ecosystems . . . . . . . . . . . . . . . . . 403

1.10.1 Signal Chain in Wounding . . . . . . . 235 3.2.1 Self-Thinning . . . . . . . . . . . . . . . . . 403

1.10.2 Pathogen Attack and Defence . . . . . 246 3.2.2 Reversible and Irreversible Site

1.10.3 Allelopathy . . . . . . . . . . . . . . . . . . . 250 Changes Related to Resource

Exploitation . . . . . . . . . . . . . . . . . . 406

3.2.3 Complexity and Non-linear

Chapter 2 Behaviour . . . . . . . . . . . . . . . . . . . . 409

3.2.4 Number of Species and Habitat

Autecology: Whole Plant Ecology . . 253

Partitioning . . . . . . . . . . . . . . . . . . 411

3.2.5 Disturbances . . . . . . . . . . . . . . . . . 417

2.1 Thermal Balance of Plants . . 255

2.1.1 The Atmosphere as Habitat . . . . . . 257

3.3 The Biogeochemical Cycles . . 425

2.1.2 Climate of Air Near the Ground . . . 263

3.3.1 Water Turnover . . . . . . . . . . . . . . . 426

2.1.3 Energy Balance of Leaves . . . . . . . . 269

3.3.2 Carbon Turnover . . . . . . . . . . . . . . 427

2.1.4 Adaptation to Temperature

3.3.3 Nitrogen Cycle . . . . . . . . . . . . . . . . 438

Extremes . . . . . . . . . . . . . . . . . . . . 270

3.3.4 Cation Turnover . . . . . . . . . . . . . . . 444

2.2 Water Relations of Plants . . . 277

3.4 Biodiversity and Ecosystem

2.2.1 Water as an Environmental Factor . 277

Processes . . . . . . . . . . . . . . . . . . 449

2.2.2 Water Transport in the Plant . . . . . 283

2.2.3 Regulation of Stomata . . . . . . . . . . 296

3.5 Case Studies at the Scale

2.2.4 Transpiration of Leaves and

Canopies . . . . . . . . . . . . . . . . . . . . 303 of Ecosystems . . . . . . . . . . . . . . 455

3.5.1 Soil Acidification and Forest

2.3 Nutrient Relations of Plants . 313 Damage . . . . . . . . . . . . . . . . . . . . . 456

2.3.1 Availability of Soil Nutrients and Ion 3.5.2 Effect of Deciduous and Coniferous

Uptake . . . . . . . . . . . . . . . . . . . . . . 313 Forests on Processes in Ecosystems 460

2.3.2 Nitrogen Nutrition . . . . . . . . . . . . . 324 3.5.3 Plants of Limestone and Siliceous

2.3.3 Sulfur Nutrition . . . . . . . . . . . . . . . 335 Rocks . . . . . . . . . . . . . . . . . . . . . . . 462

2.3.4 Phosphate Nutrition . . . . . . . . . . . . 337

2.3.5 Nutrition with Alkaline Cations . . . 338

Chapter 4

2.4 Carbon Balance . . . . . . . . . . . . 347 Syndynamics, Synchorology,

2.4.1 Net Photosynthesis: Synecology . . . . . . . . . . . . . . . . . . . . . . . 465

Physiological and Physical Basis . . 347

2.4.2 Specific Leaf Area, Nitrogen Content 4.1 Historic-Genetic Development

and Photosynthetic Capacity . . . . . 357

of Phytocenoses and Their

2.4.3 Response of Photosynthesis

Dynamics . . . . . . . . . . . . . . . . . . 467

to Environmental Factors . . . . . . . . 361

4.1.1 History of Vegetation to the End

2.4.4 Growth and Storage . . . . . . . . . . . . 373

of the Tertiary . . . . . . . . . . . . . . . . 469

2.4.5 C and N Balance in Different Types

4.1.2 Change of Climate and Vegetation

of Plants . . . . . . . . . . . . . . . . . . . . . 379

in the Pleistocene . . . . . . . . . . . . . . 472

4.1.3 Late and Postglacial Climate and

Vegetation History . . . . . . . . . . . . . 475

Chapter 3

4.1.4 Changes in Vegetation Because of

Ecology of Ecosystems . . . . . . . . . . . . 397

Human Influence . . . . . . . . . . . . . . 479

4.1.5 Basis of General Vegetation

3.1 The Ecosystem Concept . . . . . 399 Dynamics . . . . . . . . . . . . . . . . . . . . 507

3.1.1 What is an Ecosystem? . . . . . . . . . . 400 4.1.6 Stability of Plant Communities . . . . 534

3.1.2 Boundaries of Ecosystems . . . . . . . 400

3.1.3 Compartmentalisation . . . . . . . . . . 401

3.1.4 System Characteristics . . . . . . . . . . 401 a Contents IX

4.2 Synchorology: Basis of Spatial 5.2.3 Nitrogen Cycle . . . . . . . . . . . . . . . . 636

Distribution of Plants . . . . . . . 541 5.2.4 Sulfur Cycle . . . . . . . . . . . . . . . . . . . 638

4.2.1 Distribution of Plants . . . . . . . . . . . 542

5.3 Human Influence on Carbon

4.2.2 Basis of Spatial Distribution

(Phytogeography) . . . . . . . . . . . . . . 548 Balance and Significance for

4.2.3 Relationship Between Area Global Climate . . . . . . . . . . . . . . 641

and Species . . . . . . . . . . . . . . . . . . . 555

4.2.4 Biodiversity . . . . . . . . . . . . . . . . . . . 562 5.4 Significance of Changes in

Land Use for Carbon Cycles . . 649

4.3 Interactions Between Vegeta-

5.4.1 Land Use and CO Emissions . . . . . 649

tion and Abiotic and Biotic 2

5.4.2 The Kyoto Protocol: Attempts To

Environments ± Synecology . . 579 Manage the Global Carbon Cycle . . 651

4.3.1 Influences of Vegetation on the Site 580 5.4.3 Importance of Climate Change

4.3.2 Interactions Between Plants and for Europe . . . . . . . . . . . . . . . . . . . . 659

Animals . . . . . . . . . . . . . . . . . . . . . . 585

4.3.3 Interactions Between Plants . . . . . . . 602 5.5 Influence of Human Activities

on Biodiversity . . . . . . . . . . . . . . 663

5.5.1 Decrease in Biodiversity . . . . . . . . . 663

Chapter 5

Global Aspects of Plant Ecology . . . 623 5.6 Socio-economic Interactions . 669

5.6.1 Syndromes . . . . . . . . . . . . . . . . . . . 670

5.1 Global Change and Global 5.6.2 Evaluation of Risks to Biodiversity

Institutions . . . . . . . . . . . . . . . . . 625 in Ecosystems . . . . . . . . . . . . . . . . . 673

5.2 Global Material Cycles . . . . . . . 633

5.2.1 Water Cycle . . . . . . . . . . . . . . . . . . . 633 Subject Index . . . . . . . . . . . . . . . . . . . . . 679

5.2.2 Carbon Cycle . . . . . . . . . . . . . . . . . . 635 Introduction

The term ªecologyº was defined by Ernst molecular stress physiology via ecology of whole

Haeckel in 1906 in his book, Principles of Gener- organisms and the ecosystem to the temporal

al Morphology of Organisms, as follows: ªEcol- and spatial differentiation of vegetation.

ogy is the science of relations of the organism Figure 1 shows the relations between (cellu-

to the surrounding environment which includes, lar) stress or ecophysiology, whole plant phys-

in its broadest sense, all `conditions for exis- iology and synecology (i.e. the ecology of vege-

tence'. These conditions may be organic or inor- tation cover) and ecosystem science where other

ganic; both are of the greatest importance for organisms, not only plants, are increasingly con-

the form of organisms, because they force the sidered. The interrelations between stress phy-

organism to adapt.º siology, whole plant physiology and synecology

Haeckel included in the science of ecology the are very close and obvious. In contrast, the path

areas physiology, morphology and chorology from stress physiology to ecosystems runs via

(the science of the distribution of organisms) to whole plant ecology and synecology because

understand the ªconditions for existenceº and morphology, i.e. the structure of plants, and the

ªadaptationº. In this book, we try to comply responses of populations are not primarily meta-

with Haeckel's understanding of plant ecology bolic. Applied ecology includes all disciplines

and to include the breadth of ecology as it was related to human activities. These include not

demanded by Haeckel. Adaptation to the envi- only agriculture and forestry, but also global

ronment starts at the molecular and cellular lev- change. Agriculture and forestry contain also

el where environmental conditions are detected physiological aspects of high-yielding and pest-

and the responses to changes in the environment free varieties of crops and the biological interac-

are accomplished. Starting from these physiolog- tions between crop plants and other organisms,

ical mechanisms, the morphological characteris-

tics of organisms/plants become important at

the level of the whole plant. Cellular metabolic

reactions and structural (morphological and an-

atomical) organisation are the biological ªtoolsº

with which organisms make use of certain envi-

ronmental conditions, avoid them or ªadaptº to

them. The combination of physiological and Ecology

morphological ªadaptationº is particularly im-

portant for plants, as they are fixed in their hab- Stress physiology

itat and the conditions for life are determined

by the variety and numbers of the organisms of

the ecosystem and not by the individual plant

Whole plant

alone. These environmental conditions and the Synecology

ecology

interaction of a plant with the environment de-

termine ªfitnessº, i.e. the possibility for growth

and reproduction in a spatial and temporal di-

Ecology of ecosystems

mension, thus resulting in an association with

Haeckel's ªchorologyº. Haeckel's understanding

Applied ecology, global change

of ecology was broader than our present botani-

cal usage. The present book views ecology in as

nFig. 1. Areas of ecology and their position within bot-

broad a context as Haeckel did, ranging from

any,ecosystemstudiesandinappliedecology 2 Introduction

e.g. for pollination. Research on global change of these strategies, certain species are able to

also includes the assessment of possible manage- avoid extreme conditions and use or change

ment systems for earth with respect to their ef- their habitat. Annual plants form the largest

fects on climate and maintaining biodiversity. proportion of plant species in dry areas. How-

Research on global change leads to model pre- ever, their active life is limited to favourable

dictions on future effects of human activities. conditions after rain, even if this only occurs

In this book, an attempt is made, for the first sporadically, perhaps only every few years or

time, to bring together and clearly organise the even decades. In contrast, perennial species have

large subdisciplines of plant ecology. We start mechanisms that regulate the water relations

from the molecular stress and ecophysiology of and enable survival in unfavourable climatic

plants in the broadest analysis yet attempted. periods. These include, for example, special leaf

Chapter 1 lays down the molecular basis for and root anatomy that allows the species to sur-

ecological ªadaptationsº to all essential environ- vive with intact shoot systems or to change their

mental factors. This ranges from climatic factors site conditions. Hydraulic lift, for example, en-

via salt stress in the soil to environmental pollu- ables roots to transport water from deep soil

tants. The stress theory considers the basic pos- layers to the upper horizons and thus moisten

sibilities of stress responses resulting from the upper soil layers. In temperate climates, the

strains and leading to resistance; finally, these accumulation of carbon in the soil changes site

provide the basis for understanding adaptive ra- fertility. The scope for ªadaptationsº by whole

diation of genotypes, and the processes leading plants is very broad, as are the responses of cells

to the evolution of new species. Plants not only to stress. They range from leaf structure and

react to stress in the sense of a response, the so- leaf movement, via the formation of variably di-

called feed-back reponse. There are also pre- mensioned vessels in the stem, to differentiation

paratory adaptations to changing environmental of the roots. In Chapter 2, the use of resources

conditions, the so-called feed-forward reactions, by whole plants is discussed. This includes the

setting off before an organism is stressed (e.g. plant±water relations, the heat and nutrient bal-

pre-winter frost hardening). In both cases, signal ances and the carbon relations.

chains are activated, leading to changes in the Cellular metabolism and structural character-

physiological/cell biological performance of istics are not only the basis for the spatial and

plants, enabling them to continue to exist under temporal patterns of plant species, dealt within

new conditions. The response to one stress fac- synecology (Chap. 4), but also the basis for ele-

tor often protects the organism also from dam- ment cycles in ecosystems, which are charac-

age by other stresses (ªcross-protectionº). This terisedbythediversityofspeciesandformsofor-

results in responses to a variety of stresses re- ganisation.Theseincludeindirectinteractionsbe-

sulting from a changing environment where not tween individual plants and other plant species.

one single factor (e.g. heat or drought), but mul- Here applies the wisdom that: ªEven the most

tiple stress types are acting in combination. The pious cannot live in peace if it does not please

basic principles of avoidance (as a sort of feed- the nasty neighbourª. Competition exists in the

forward response) and tolerance (as a sort of effective use of resources on limited space. If the

feed-back response) to stress are not only re- resources become scarce, ªefficiencyº means a

stricted to the level of ecophysiology, but occur better use of limiting resources at the cost of

also in responses of wholeplants, inthe distribu- the neighbour. This, of course, does not always

tionofspeciesandplantcommunities,particular- imply saving resources or using them most eco-

ly at extreme sites. nomically. Indeed, it may be more useful to use

At the level of the organism, we consider the more resources than required, if this brings ad-

plant as a whole and the relations between its vantages in competition with the neighbours.

organs from the root to the leaf, flower and Growth also plays an important role in ecosys-

seed. At the level of whole plant ecology new, tems, and the ªecological equilibriumº of an eco-

not (primary) metabolic characteristics are system probably does not exist in ªnatureº as it

added: although these are genetically deter- is. Metabolic cycles in ecosystems are not as

mined, they may be modified within limits. closed as previously assumed. This means that

These include plant structures including size the actual status as it may be observed as a mo-

and the life cycle (phenology, life span, strate- mentary picture of a system is in the long term

gies for reproduction and distribution). Because verydynamic. Not allprocesses ofasystemmove a Introduction 3

dry

alkaline

Limits of

a positive

shade

carbon balance

Flowering

and fruiting

possible

Without

competition

Temporal and

geographical

cold warm

range with

competition

acid

sunny

wet

nFig.2.Distributionofaspeciesdependsondifferentenvironmentalfactors.Theactualdistributionareaissignificantly

smaller thanthe potential areas ofdistribution whicharereachedwithoutcompetition attheextremelimits offlowering

or at the boundaries of a positive material balance. In the example shown, temperature is the dominant factor, but this

maydifferinothercases.Accordingtothespecies,thelimitsofdistributionchange

linearly in one direction.There are strengthening use of the available resources. In synecology, the

and weakening processes with a consequential broad spectrum of responses at the cellular and

complex, non-linear temporal behaviour. The sci- whole plant level is replaced by the enormous

entific basis of ecosystems is, for the first time, diversity of species (350,000 species of vascular

presented in Chapter 3 of this volume. General plants) which determine in different proportions

conclusions are drawn about how individual or- the composition of the vegetation cover of the

ganisms interact within the diversity of vegeta- earth. In Chapter 4, the historical and spatial di-

tion. This leads to the question about the degree mensions of species distributions and their bio-

towhichvegetationismorethanthesumofitsin- logical interactions are discussed.

dividualplants.Manycharacteristicsofvegetation Combining the ecology of ecosystems with

result from material fluxes which dictate the per- the field of synecology enables us to understand

formance of individual plants. For example, the also the distribution of species. Both the poten-

ªaero-dynamic roughnessº of the surface of vege- tial and actual areas (Fig. 2) are determined by

tation determines coupling to the meteorological several parameters. For example, considering

conditions in the atmosphere and thus deter- only the carbon balances, a plant species could

mines the survival of plant individuals or a spe- grow on a much larger area than the region in

cies inthe vegetation. It is only by large numbers which it actually reproduces. However, even this

of individuals of the same species which,through region is limited by different types of competi-

distribution of seeds or other ways of propaga- tion with other species, so that the area even-

tion, determine the habitat in relation to a dy- tually occupied is even further restricted. Agri-

namic diversity of other species. cultural crop plants (maize, beans, wheat, potato,

Synecology is the next higher level of plant soya and many others) are an interesting exam-

ecology, extending to populations based on the ple of evolution in a geographically limited area

strategies of propagation and distribution. Syn- (theso-calledgeneticcentres oforigin),butthese

ecology does not consider the fate of a single in- species are now distributed worldwide after do-

dividual, but the dynamic spatial and temporal mestication and management by humans.

behaviour of populations, including population The science of geobotany relates to global as-

growth, homoeostasis and decline. Only in ex- pects in plant ecology, which are included in the

ceptional cases does a single species form a veg- term global change, where the direct and indi-

etation. Generally, natural vegetation includes a rect influences of man through land use,

diversity of species which make complementary changes in land use and the subsequent changes