Insights on current research and recent developments in understanding global savanna systems
Increasingly recognized as synonymous with tropical grassy biomes, savannas are found in tropical and sub-tropical climates as well as warm, temperate regions of North America. Savanna Woody Plants and Large Herbivores examines the interactions between woody plants and browsing mammals in global savannas - focusing primarily on the C4 grassy ecosystems with woody components that constitute the majority of global savannas - and discusses contemporary savanna management models and applications.
This much-needed addition to current research examines topics including the varying behavior of browsing mammals, the response to browsing by woody species, and the factors that inhibit forage intake. Contributions from an international team of active researchers and experts compare and contrast different savanna ecosystems, offering a global perspective on savanna functioning, the roles of soil and climate in resource availability and organism interaction, and the possible impacts of climate change across global savannas.
- Fills a gap in literature on savanna management issues, including biodiversity conservation and animal production
- Applies concepts developed in other biomes to future savanna research
- Complements contemporary books on savanna or large herbivore ecology
- Focuses on the woody component of savanna ecosystems and large herbivore interactions in savannas
- Compares tree-mammal systems of savannas and other eco-systems of temperate and boreal regions
- Provides numerous case studies of plant-mammal interactions from various savanna ecosystems
Savanna Woody Plants and Large Herbivores is a valuable addition to those in fields such as ecology, wildlife and conservation biology, natural resource management, and environmental science.
Table of Contents
List of Contributors xv
Preface xix
Part I Introduction 1
1 Distribution and Determinants of Savannas 3
Sally Archibald, William J. Bond, William Hoffmann, Caroline Lehmann, Carla Staver, and Nicola Stevens
1.1 Introduction 3
1.2 Evolutionary History of Savanna Vegetation and Fauna 4
1.3 Defining Savannas 7
1.3.1 Are Savannas Tropical Systems? 7
1.3.2 Distinguishing Savannas from Grasslands 7
1.3.3 Distinguishing Savannas from Forests 8
1.4 Global Determinants of Savannas 9
1.4.1 Mesic Transition: Points of Contention 10
1.4.1.1 The Role of Nutrients 10
1.4.1.2 Rainfall Seasonality 10
1.4.2 Mesic Transition: Toward Resolution 11
1.4.3 Mesic Transition: Unresolved Ideas 12
1.4.4 Arid Transition 12
1.4.5 Arid Transition: Toward Resolution 13
1.4.6 Determinants of Temperate Savannas 14
1.5 Functional Differences Between Savannas 14
1.5.1 Temperate vs Tropical Savannas 14
1.5.2 Functional Differences Within Tropical Savannas 15
1.6 Conclusions and the Future of Savanna Ecosystems 17
References 17
2 African and Asian Savannas: Comparisons of Vegetation Composition and Drivers of Vegetation Structure and Function 25
Jayashree Ratnam, Chintan Sheth, and Mahesh Sankaran
2.1 Introduction 25
2.2 Climate and Vegetation Formations 27
2.3 Fine‐Leaved and Broad‐Leaved Savannas: Vegetation Structure, Composition, and Geographic Distribution 30
2.4 Role of Bottom‐Up Drivers in Regulating Vegetation Structure: Climate and Soil Nutrients 33
2.5 Role of Top‐Down Forces: Fire and Herbivory 36
2.6 African and Asian Savannas in the Anthropocene 40
References 42
3 Savannas of Australia and New Guinea: Vegetation and the Functional Role of Extant and Extinct Fauna 51
Garry D. Cook, William J. Bond, Edmund C. February, and Richard J. Williams
3.1 Introduction 51
3.2 The Biota of Australia’s and New Guinea’s Savannas 51
3.3 Climate, Landforms, and Fire 53
3.4 Human History and Impacts 54
3.5 Are Native Mammals Irrelevant? 55
3.6 Was Ecosystem Functioning Different Prior to Human Dispersal to Australia? 57
3.7 Critique of the “Nutrient Poverty/Intense Fire” Theory 58
3.8 Australia’s Lost Megafauna 61
3.9 Habitat Variation and the Pleistocene Megafauna 64
3.10 Impacts of Herbivores in Australian Savannas 64
3.11 Toward a New Hypothesis of Plant-Animal Interactions in Australian Savannas 66
References 67
4 South American Savannas 77
Fabian Borghetti, Eduardo Barbosa, Leandro Ribeiro, José Felipe Ribeiro, and Bruno Machado Teles Walter
4.1 Introduction 77
4.2 Origin of South American Savannas 77
4.3 Distribution and Diversity of South American Savannas 78
4.4 Northern Savannas 80
4.4.1 Colombo-Venezuelan Llanos 80
4.4.1.1 Orinoco Llanos 80
4.4.1.2 Llanos Orientales 84
4.4.2 Gran Sabana 85
4.4.3 Rio Branco-Rupununi Savannas 85
4.4.3.1 Rio Branco Savannas 86
4.4.3.2 Rupununi Savannas 86
4.4.4 Savannas of Amapá 87
4.5 Southern Savannas 87
4.5.1 Savannas of Humaitá 87
4.5.2 Savannas of Pará 87
4.5.3 Beni Savannas 88
4.5.4 Cerrado 89
4.5.4.1 Cerrado (Sensu Stricto) 91
4.5.4.2 Cerrado Park 92
4.5.4.3 Palm Groves 92
4.5.4.4 Vereda 92
4.5.4.5 Campo Limpo (“Open Grassland”) 92
4.5.4.6 Campo Sujo (“Dense Grassland”) 92
4.5.4.7 Campo Rupestre (“Rocky Field”) 96
4.5.5 Pantanal 96
4.5.6 Chaco 97
4.6 Effects of Water Deficit, Herbivory, and Fire on Vegetation Dynamics 102
4.6.1 Water Deficit 102
4.6.2 Herbivory 103
4.6.3 Fire 104
4.7 Climate Change, Anthropogenic Pressure, and the Future 106
4.8 Concluding Remarks 109
4.9 Acknowledgments 109
References 110
5 Savannas of North America 123
Norma L. Fowler and Brian Beckage
5.1 Introduction 123
5.1.1 Definitions 123
5.1.2 Climatic Patterns 126
5.2 Fire 127
5.3 Grazing 128
5.4 Biodiversity 129
5.5 Conservation 129
5.6 Oak Savannas 130
5.6.1 Central US, South‐Central Canada, Northern Sierra Madre (Mexico) Oak Savannas 130
5.6.2 California Oak Savannas 132
5.6.3 South‐West (Arizona, New Mexico, Northern Mexico) Oak Savannas 132
5.6.4 Pacific Northwest Oak Savannas 132
5.6.5 East‐Central US: Glades, Barrens, and Other Forest Openings 132
5.6.6 Oak‐Dominated Shrub Savannas 133
5.7 Pine Savannas 133
5.7.1 South‐Eastern US Pine Savannas 133
5.7.2 Rocky Mountains Pine Savannas 134
5.8 Juniper Savannas 135
5.8.1 Juniper Savannas in the Western Mountains 135
5.8.2 Eastern Red Cedar Savannas 138
5.8.3 South‐Central US and Northern Sierra Madre Oriental Juniper Savannas 138
5.9 Mesquite Savannas 138
5.10 Northern and High‐Elevation Savannas 140
5.11 Shrub Savannas 140
5.12 Conclusions 141
5.13 Acknowledgments 141
References 141
6 Socioeconomic Value of Savannas 151
Wayne Twine
6.1 Introduction 151
6.2 Land Tenure and Land Use 153
6.3 Livestock Farming 155
6.3.1 Overview 155
6.3.2 Commercial Livestock Farming 157
6.3.3 Subsistence Livestock Farming 157
6.4 Wildlife Industry 159
6.4.1 Overview 159
6.4.2 Ecotourism 161
6.4.3 Hunting 162
6.4.4 Animal Products 163
6.4.5 Game Breeding and Live Sales 164
6.5 Commercial Timber 164
6.6 Non‐timber Products 164
6.6.1 Uses 164
6.6.2 Economic Value 166
6.6.2.1 Non‐monetary Income 166
6.6.2.2 Cash Income 167
6.6.2.3 Environmental Income 168
6.7 Conclusion 169
References 170
Part II Herbivores 181
7 Ecology of Smaller Animals Associated with Savanna Woody Plants: The Value of the Finer Details 183
Colleen Seymour and Grant Joseph
7.1 Introduction 183
7.2 Woody Plant Seed Herbivory 184
7.2.1 Seed Herbivores 184
7.3 Woody Plant Seed and Fruit Dispersal 187
7.3.1 Diplochory 187
7.3.1.1 Seed Dispersal by Birds 188
7.3.1.2 Invertebrate Seed Dispersal 189
7.3.2 Fruit Dispersal 189
7.4 Woody Plant Seedling Establishment 190
7.5 Leaves and Herbivory 191
7.6 Pollination and Nectarivory 193
7.7 Nutrient Cycling 195
7.8 Conclusions 199
References 201
8 Evolution of Large Mammal Herbivores in Savannas 213
Daryl Codron
8.1 Introduction 213
8.2 Herbivore Dietary Niches 215
8.3 Diversification of Browsers and Grazers 220
8.4 Effects of Vegetation Change 223
8.5 Herbivore Body Size 226
8.6 Pleistocene Extinctions and Contemporary Herbivore Diversity 228
8.7 Summary 233
References 234
9 Browser Population-Woody Vegetation Relationships in Savannas: From Bites to Landscapes 245
Melissa H. Schmitt and Adrian M. Shrader
9.1 Introduction 245
9.2 Factors Influencing Diet Selection 246
9.2.1 Browser Traits that Influence Foraging 247
9.2.1.1 Body Size 247
9.2.1.2 Gut Morphology 248
9.2.2 Woody Plant Traits that Influence Browsers 248
9.2.2.1 Seasonality 248
9.2.2.2 High Nutrient Levels (Positive) 249
9.2.2.3 Chemical Defenses (Negative) 250
9.2.2.4 Physical Defenses 252
9.2.2.5 Mutualisms 253
9.2.3 Herbivore Coping Mechanisms 253
9.3 Browser Impacts on Vegetation 255
9.3.1 Biomass Removal (Small and Large) 255
9.3.2 Impacts on Seeds 256
9.4 Feedback from Browsed Plants to Browsers 257
9.4.1 Lowered Food Availability 257
9.4.2 Habitat Changes 259
9.4.3 Change in Landscapes of Fear 260
9.4.4 New Growth 261
9.4.5 Nutrient Hot Spots 261
9.4.6 Browsing Lawns 261
9.5 Scaling from Bites to Browser Population Dynamics 262
9.5.1 Population Dynamics 263
9.5.2 Intake and Population Size 263
9.5.3 Food Availability, Food Quality, and Population Dynamics 264
9.5.4 Future Research 265
9.6 Conclusions 265
References 265
10 Predator Effects on Herbivore Dynamics and Behavior: What Mechanisms Lead to Trophic Cascades in Savannas? 279
Simon Chamaillé‐Jammes, Marion Valeix, and Joris Cromsigt
10.1 Introduction 279
10.2 Consumptive Effects of Predation 280
10.2.1 Concepts, Theory, and Evidence from Biomes Other than Savanna 280
10.2.1.1 Additive Versus Compensatory Mortality 281
10.2.1.2 Predator Functional Response 282
10.2.1.3 Ecosystem Characteristics 284
10.2.2 Evidence from Savannas 285
10.2.2.1 Additive Versus Compensatory Mortality 286
10.2.2.2 Predator Functional Response 288
10.2.2.3 Ecosystem Characteristics 288
10.3 Non‐consumptive Effects of Predation 290
10.3.1 Concepts, Theory, and Evidence from Biomes Other than Savanna 290
10.3.1.1 Landscape Use 290
10.3.1.2 Vigilance and Grouping Strategies 291
10.3.1.3 The Importance of Food-Safety Trade‐Offs 292
10.3.1.4 Demographic Costs of Behavioral Adjustments 293
10.3.2 Evidence from Savannas 293
10.3.2.1 Landscape Use 293
10.3.2.2 Vigilance and Grouping Strategies 295
10.4 Cascading Effects of Consumptive and Non‐consumptive Effects of Predation on Lower Trophic Levels 296
10.5 The Times they are A‐changin’: Changes in Megaherbivory, Migration Patterns, and Climate 297
References 299
Part III Woody Plants 309
11 Physiological Traits of Savanna Woody Species: Adaptations to Resource Availability 311
Edmund C. February, Corli Coetsee, Garry D. Cook, Jayashree Ratnam, and Benjamin Wigley
11.1 Introduction 311
11.2 Soil Nutrients and Root Responses 314
11.3 Leaf Phenology and Available Water 317
11.4 Competition for Resources 321
References 323
12 Patterns and Determinants of Woody Plant Growth in Savannas 331
Anthony Swemmer and David Ward
12.1 Introduction: The Relevance of Growth Rates 331
12.2 Determinants of Growth Rates 333
12.2.1 Seedlings 334
12.2.2 Saplings 342
12.2.3 Adults 344
12.2.4 Demographic Significance 344
12.2.4.1 Growth Trajectory 345
12.2.4.2 Size or Age of Individuals 345
12.2.4.3 Above vs Below Ground 345
12.2.4.4 Plant Part 347
12.2.4.5 Interacting Factors 347
12.2.4.6 Experimental Conditions 348
12.2.4.7 Individual vs Population Growth 348
12.2.4.8 Time and Size 348
12.2.4.9 Species 348
12.2.5 The Value of Long‐Term Research 349
12.3 Modeling Growth 350
12.3.1 Insights from Published Data 351
12.3.2 Predicting Rates from Environment or Phylogeny 353
12.3.3 Deficiencies in Growth Rate Data 356
12.4 Conclusions 357
12.A Appendix: Growth Rate Data 358
References 428
13 Fire and Browsers in Savannas: Traits, Interactions, and Continent‐Level Patterns 439
Gareth P. Hempson, Sally Archibald, and Carla Staver
13.1 Introduction 439
13.2 Browser and Fire Attributes 440
13.2.1 How do Fire and Browsers Compare as Consumers of Woody Plants? 440
13.2.1.1 Frequency and Seasonality 440
13.2.1.2 Selectivity, Intensity, and Scale 440
13.2.1.3 Elimination Thresholds 442
13.2.2 Plant Responses to Fire and Browsing 442
13.2.2.1 Defense Traits 442
13.2.2.2 Architecture 443
13.2.2.3 Resprouting and Bud Protection 444
13.2.2.4 Fire‐ and Browser‐Traps 445
13.2.2.5 Reproduction and Seedling Recruitment 446
13.3 Fire-Browser Interactions 447
13.3.1 Consequences of Fire for Browsers 447
13.3.1.1 Post‐Fire Environment 448
13.3.1.2 Woody Plant Regeneration 449
13.3.1.3 Decadal Fire Regimes 450
13.3.2 Browser Feedbacks to Fire 451
13.3.2.1 Browser Facilitation of Fire 451
13.3.2.2 Negative Feedbacks of Mixed‐Feeders 451
13.3.3 Fire-Browser Vegetation Impacts 452
13.3.3.1 Sapling Escape 452
13.3.3.2 Elephant Bark Stripping and Canopy Breakage 452
13.4 Biogeography of Fire and Browsing in Africa 453
13.4.1 Continental‐Scale Patterns of Fire and Browsing 455
13.4.2 Fire-Browser Regimes 457
13.4.3 Fine‐ vs Broad‐Leaved Savannas 457
13.5 Synthesis 460
References 460
14 Woody Plant Architecture and Effects on Browsing Herbivores in Savannas 469
Tristan Charles‐Dominique, Jean‐Francois Barczi , and Simon Chamaillé‐Jammes
14.1 Introduction 469
14.2 Factors Limiting Bite Size 471
14.3 Factors Limiting Biting Rate 474
14.4 Simulating Plant-Herbivore Interactions at the Individual Plant Scale 476
14.4.1 Plant Growth Model 477
14.4.2 Virtual Browsing and Consequences for Plant Fitness 478
14.4.3 Virtual Experiment Set‐up 478
14.4.4 Simulation Results 480
14.4.4.1 Effect of Leaf Size 481
14.4.4.2 Effect of Short Shoots 481
14.4.4.3 Effect of Spines 482
14.4.4.4 Effect of Cage Architecture 482
14.4.4.5 Effect of Short Shoot Induction 482
14.4.4.6 Effect of Sprouting 482
14.4.5 Significance of Simulation Results 482
14.5 Future Directions for Modeling Plant-Herbivore Interactions 483
Acknowledgments 483
14.A Appendix 484
References 484
15 Browsing Herbivore-Woody Plant Interactions in Savannas 489
Peter Frank Scogings and Juan H. Gowda
15.1 Introduction 489
15.1.1 The raison d’être 489
15.1.2 Approach 490
15.2 Feedback Between Woody Individuals and Browsing Herbivores 492
15.2.1 Shoot Growth 492
15.2.2 Spinescence 493
15.2.3 Nutrients and Phenolics 494
15.2.4 Is Positive Feedback Widespread? 495
15.3 Selective Browsing and Shifts in Woody Vegetation Composition and Structure 497
15.3.1 Recruitment and Mortality 497
15.3.2 Community Composition and Structure 500
15.4 Linking Responses of Woody Individuals and Communities to Functional Traits 501
15.5 Future Directions 504
15.5.1 Key Gaps 504
15.5.2 Standardizing Methods 505
References 539
16 Mesobrowser Abundance and Effects on Woody Plants in Savannas 551
David J. Augustine, Peter Frank Scogings, and Mahesh Sankaran
16.1 Introduction551
16.2 Mesobrowser Abundance in Savannas 552
16.3 Mesobrowser Diets in Savannas 559
16.4 Mesobrowser Effects on Woody Plant Communities 561
16.4.1 Hluhluwe‐iMfolozi Park, South Africa 564
16.4.2 Central Laikipia, Kenya 565
16.4.3 Chobe National Park, Botswana 567
16.4.4 Kruger National Park, South Africa 568
16.5 Evidence from Long‐Term Perspectives 569
16.6 The Influence of High Densities of Individual Mesobrowser Species 570
16.7 Water, Nutrients, and Mesobrowsers 571
16.8 Synthesis 573
Acknowledgments 576
References 576
17 Megabrowser Impacts on Woody Vegetation in Savannas 585
Norman Owen‐Smith, Bruce Page, Gabriella Teren, and Dave J. Druce
17.1 Introduction 585
17.2 Use of Woody Plants Versus Grasses and Other Plant Forms 586
17.3 Selection for Size Classes and Woody Plant Parts 589
17.4 Plant Damage Imposed and Mortality 590
17.5 Plant Species Selected 592
17.6 Landscape Transformations Caused by Elephants, Along with Fire 599
17.7 A Cautionary Note 602
17.8 Overview 602
References 604
18 Indirect Effects of Browsing Herbivores in Savannas 613
Corli Coetsee, Dario Fornara, Antoinette Veldtman, and Benjamin Wigley
18.1 Introduction 613
18.2 Indirect Effects of Browsers on Other Fauna 614
18.2.1 Mammals 614
18.2.1.1 Large Herbivore Effects on Rodents 614
18.2.1.2 Mesobrowser Effects on Other Herbivores 615
18.2.1.3 Megaherbivore Effects on Mesoherbivores 616
18.2.1.4 Interactions Among Browsers Where the Type of Browser is Not Apparent 616
18.2.1.5 Interactions Among Megaherbivores 617
18.2.1.6 Summary 617
18.2.2 Birds 617
18.2.2.1 Summary 619
18.2.3 Reptiles and Amphibians 619
18.2.3.1 Summary 619
18.2.4 Invertebrates 619
18.2.4.1 Summary 621
18.3 Effects on Ecosystem Processes 622
18.3.1 Carbon Cycling 622
18.3.1.1 Consumption of Vegetation by Browsers Affects Ecosystem Carbon Pools 622
18.3.1.2 Changes in Litterfall Affect Soil Carbon 625
18.3.1.3 Global Change Can Override the Effects of Herbivory on Soil Carbon 625
18.3.1.4 Summary 626
18.3.2 Soil Nutrient Cycling and Soil Nutrient Pools 626
18.3.2.1 Changes in Litter Quality 626
18.3.2.2 Herbivore Effects on both Litter Quality and Quantity 629
18.3.2.3 Summary 629
18.4 Conclusions 629
References 630
Part IV Synthesis 643
19 Water Limitation, Fire, and Savanna Persistence: A Conceptual Model 645
Brian Beckage, Gabriela Bucini, Louis J. Gross, William J. Platt, Steven I. Higgins, Norma L. Fowler, Matthew G. Slocum, and Caroline Farrior
19.1 Introduction 645
19.2 Conceptual Model 646
19.2.1 Water Limitation 648
19.2.2 Fire 650
19.2.3 Fire Feedbacks 651
19.2.4 Other Processes 652
19.3 Summary 653
Acknowledgments 654
References 654
20 Savanna Ecosystem Models: What Should a Clever Modeler Code? 661
Gregory Kiker and Peter Frank Scogings
20.1 Introduction 661
20.2 Local‐Scale Aspects of Woody Plant-Browser Interactions 662
20.3 Model Designs for Plant-Herbivore Interactions 663
20.3.1 Plant‐Focused Models 666
20.3.2 Herbivore‐Based Models 668
20.3.3 Integrated Models: Adding Complexity into Plant-Herbivore Models 670
20.4 Discussion 672
References 674
21 Woody Plants and Large Herbivores in Savannas: Ancient Past - Uncertain Future 683
Peter Frank Scogings and Mahesh Sankaran
21.1 Introduction 683
21.2 Woody Plants 685
21.3 Large Herbivores 688
21.4 Interactions Between Woody Plants and Browsers 690
21.4.1 Adaptations of Woody Plants to Browsing by Mesobrowsers 690
21.4.2 Woody Community Responses to Mesobrowsers and Megaherbivores 692
21.4.3 Indirect Effects of Browsing 696
21.5 Models 698
21.5.1 General Conceptual (Qualitative) Models 698
21.5.2 Mathematical (Quantitative) Models 700
21.6 The Future 701
References 703
Index 713
