Savanna Woody Plants and Large Herbivores

PETER FRANK SCOGINGS is Associate Professor, School of Life Sciences, University of KwaZulu-Natal, South Africa. MAHESH SANKARAN is Reader, National Centre for Biological Sciences, India, and Lecturer, Institute of Integrative & Comparative Biology, Faculty of Biological Sciences, University of Leeds, UK.

• List of Contributors xvPreface xixPart I Introduction 11 Distribution and Determinants of Savannas 3Sally Archibald, William J. Bond, William Hoffmann, Caroline Lehmann, Carla Staver, and Nicola Stevens1.1 Introduction 31.2 Evolutionary History of Savanna Vegetation and Fauna 41.3 Defining Savannas 71.3.1 Are Savannas Tropical Systems? 71.3.2 Distinguishing Savannas from Grasslands 71.3.3 Distinguishing Savannas from Forests 81.4 Global Determinants of Savannas 91.4.1 Mesic Transition: Points of Contention 101.4.1.1 The Role of Nutrients 101.4.1.2 Rainfall Seasonality 101.4.2 Mesic Transition: Toward Resolution 111.4.3 Mesic Transition: Unresolved Ideas 121.4.4 Arid Transition 121.4.5 Arid Transition: Toward Resolution 131.4.6 Determinants of Temperate Savannas 141.5 Functional Differences Between Savannas 141.5.1 Temperate vs Tropical Savannas 141.5.2 Functional Differences Within Tropical Savannas 151.6 Conclusions and the Future of Savanna Ecosystems 17References 172 African and Asian Savannas: Comparisons of Vegetation Composition and Drivers of Vegetation Structure and Function 25Jayashree Ratnam, Chintan Sheth, and Mahesh Sankaran2.1 Introduction 252.2 Climate and Vegetation Formations 272.3 Fine‐Leaved and Broad‐Leaved Savannas: Vegetation Structure, Composition, and Geographic Distribution 302.4 Role of Bottom‐Up Drivers in Regulating Vegetation Structure: Climate and Soil Nutrients 332.5 Role of Top‐Down Forces: Fire and Herbivory 362.6 African and Asian Savannas in the Anthropocene 40References 423 Savannas of Australia and New Guinea: Vegetation and the Functional Role of Extant and Extinct Fauna 51Garry D. Cook, William J. Bond, Edmund C. February, and Richard J. Williams3.1 Introduction 513.2 The Biota of Australia’s and New Guinea’s Savannas 513.3 Climate, Landforms, and Fire 533.4 Human History and Impacts 543.5 Are Native Mammals Irrelevant? 553.6 Was Ecosystem Functioning Different Prior to Human Dispersal to Australia? 573.7 Critique of the “Nutrient Poverty/Intense Fire” Theory 583.8 Australia’s Lost Megafauna 613.9 Habitat Variation and the Pleistocene Megafauna 643.10 Impacts of Herbivores in Australian Savannas 643.11 Toward a New Hypothesis of Plant–Animal Interactions in Australian Savannas 66References 674 South American Savannas 77Fabian Borghetti, Eduardo Barbosa, Leandro Ribeiro, José Felipe Ribeiro, and Bruno Machado Teles Walter4.1 Introduction 774.2 Origin of South American Savannas 774.3 Distribution and Diversity of South American Savannas 784.4 Northern Savannas 804.4.1 Colombo–Venezuelan Llanos 804.4.1.1 Orinoco Llanos 804.4.1.2 Llanos Orientales 844.4.2 Gran Sabana 854.4.3 Rio Branco–Rupununi Savannas 854.4.3.1 Rio Branco Savannas 864.4.3.2 Rupununi Savannas 864.4.4 Savannas of Amapá 874.5 Southern Savannas 874.5.1 Savannas of Humaitá 874.5.2 Savannas of Pará 874.5.3 Beni Savannas 884.5.4 Cerrado 894.5.4.1 Cerrado (Sensu Stricto) 914.5.4.2 Cerrado Park 924.5.4.3 Palm Groves 924.5.4.4 Vereda 924.5.4.5 Campo Limpo (“Open Grassland”) 924.5.4.6 Campo Sujo (“Dense Grassland”) 924.5.4.7 Campo Rupestre (“Rocky Field”) 964.5.5 Pantanal 964.5.6 Chaco 974.6 Effects of Water Deficit, Herbivory, and Fire on Vegetation Dynamics 1024.6.1 Water Deficit 1024.6.2 Herbivory 1034.6.3 Fire 1044.7 Climate Change, Anthropogenic Pressure, and the Future 1064.8 Concluding Remarks 1094.9 Acknowledgments 109References 1105 Savannas of North America 123Norma L. Fowler and Brian Beckage5.1 Introduction 1235.1.1 Definitions 1235.1.2 Climatic Patterns 1265.2 Fire 1275.3 Grazing 1285.4 Biodiversity 1295.5 Conservation 1295.6 Oak Savannas 1305.6.1 Central US, South‐Central Canada, Northern Sierra Madre (Mexico) Oak Savannas 1305.6.2 California Oak Savannas 1325.6.3 South‐West (Arizona, New Mexico, Northern Mexico) Oak Savannas 1325.6.4 Pacific Northwest Oak Savannas 1325.6.5 East‐Central US: Glades, Barrens, and Other Forest Openings 1325.6.6 Oak‐Dominated Shrub Savannas 1335.7 Pine Savannas 1335.7.1 South‐Eastern US Pine Savannas 1335.7.2 Rocky Mountains Pine Savannas 1345.8 Juniper Savannas 1355.8.1 Juniper Savannas in the Western Mountains 1355.8.2 Eastern Red Cedar Savannas 1385.8.3 South‐Central US and Northern Sierra Madre Oriental Juniper Savannas 1385.9 Mesquite Savannas 1385.10 Northern and High‐Elevation Savannas 1405.11 Shrub Savannas 1405.12 Conclusions 1415.13 Acknowledgments 141References 1416 Socioeconomic Value of Savannas 151Wayne Twine6.1 Introduction 1516.2 Land Tenure and Land Use 1536.3 Livestock Farming 1556.3.1 Overview 1556.3.2 Commercial Livestock Farming 1576.3.3 Subsistence Livestock Farming 1576.4 Wildlife Industry 1596.4.1 Overview 1596.4.2 Ecotourism 1616.4.3 Hunting 1626.4.4 Animal Products 1636.4.5 Game Breeding and Live Sales 1646.5 Commercial Timber 1646.6 Non‐timber Products 1646.6.1 Uses 1646.6.2 Economic Value 1666.6.2.1 Non‐monetary Income 1666.6.2.2 Cash Income 1676.6.2.3 Environmental Income 1686.7 Conclusion 169References 170Part II Herbivores 1817 Ecology of Smaller Animals Associated with Savanna Woody Plants: The Value of the Finer Details 183Colleen Seymour and Grant Joseph7.1 Introduction 1837.2 Woody Plant Seed Herbivory 1847.2.1 Seed Herbivores 1847.3 Woody Plant Seed and Fruit Dispersal 1877.3.1 Diplochory 1877.3.1.1 Seed Dispersal by Birds 1887.3.1.2 Invertebrate Seed Dispersal 1897.3.2 Fruit Dispersal 1897.4 Woody Plant Seedling Establishment 1907.5 Leaves and Herbivory 1917.6 Pollination and Nectarivory 1937.7 Nutrient Cycling 1957.8 Conclusions 199References 2018 Evolution of Large Mammal Herbivores in Savannas 213Daryl Codron8.1 Introduction 2138.2 Herbivore Dietary Niches 2158.3 Diversification of Browsers and Grazers 2208.4 Effects of Vegetation Change 2238.5 Herbivore Body Size 2268.6 Pleistocene Extinctions and Contemporary Herbivore Diversity 2288.7 Summary 233References 2349 Browser Population–Woody Vegetation Relationships in Savannas: From Bites to Landscapes 245Melissa H. Schmitt and Adrian M. Shrader9.1 Introduction 2459.2 Factors Influencing Diet Selection 2469.2.1 Browser Traits that Influence Foraging 2479.2.1.1 Body Size 2479.2.1.2 Gut Morphology 2489.2.2 Woody Plant Traits that Influence Browsers 2489.2.2.1 Seasonality 2489.2.2.2 High Nutrient Levels (Positive) 2499.2.2.3 Chemical Defenses (Negative) 2509.2.2.4 Physical Defenses 2529.2.2.5 Mutualisms 2539.2.3 Herbivore Coping Mechanisms 2539.3 Browser Impacts on Vegetation 2559.3.1 Biomass Removal (Small and Large) 2559.3.2 Impacts on Seeds 2569.4 Feedback from Browsed Plants to Browsers 2579.4.1 Lowered Food Availability 2579.4.2 Habitat Changes 2599.4.3 Change in Landscapes of Fear 2609.4.4 New Growth 2619.4.5 Nutrient Hot Spots 2619.4.6 Browsing Lawns 2619.5 Scaling from Bites to Browser Population Dynamics 2629.5.1 Population Dynamics 2639.5.2 Intake and Population Size 2639.5.3 Food Availability, Food Quality, and Population Dynamics 2649.5.4 Future Research 2659.6 Conclusions 265References 26510 Predator Effects on Herbivore Dynamics and Behavior: What Mechanisms Lead to Trophic Cascades in Savannas? 279Simon Chamaillé‐Jammes, Marion Valeix, and Joris Cromsigt10.1 Introduction 27910.2 Consumptive Effects of Predation 28010.2.1 Concepts, Theory, and Evidence from Biomes Other than Savanna 28010.2.1.1 Additive Versus Compensatory Mortality 28110.2.1.2 Predator Functional Response 28210.2.1.3 Ecosystem Characteristics 28410.2.2 Evidence from Savannas 28510.2.2.1 Additive Versus Compensatory Mortality 28610.2.2.2 Predator Functional Response 28810.2.2.3 Ecosystem Characteristics 28810.3 Non‐consumptive Effects of Predation 29010.3.1 Concepts, Theory, and Evidence from Biomes Other than Savanna 29010.3.1.1 Landscape Use 29010.3.1.2 Vigilance and Grouping Strategies 29110.3.1.3 The Importance of Food–Safety Trade‐Offs 29210.3.1.4 Demographic Costs of Behavioral Adjustments 29310.3.2 Evidence from Savannas 29310.3.2.1 Landscape Use 29310.3.2.2 Vigilance and Grouping Strategies 29510.4 Cascading Effects of Consumptive and Non‐consumptive Effects of Predation on Lower Trophic Levels 29610.5 The Times they are A‐changin’: Changes in Megaherbivory, Migration Patterns, and Climate 297References 299Part III Woody Plants 30911 Physiological Traits of Savanna Woody Species: Adaptations to Resource Availability 311Edmund C. February, Corli Coetsee, Garry D. Cook, Jayashree Ratnam, and Benjamin Wigley11.1 Introduction 31111.2 Soil Nutrients and Root Responses 31411.3 Leaf Phenology and Available Water 31711.4 Competition for Resources 321References 32312 Patterns and Determinants of Woody Plant Growth in Savannas 331Anthony Swemmer and David Ward12.1 Introduction: The Relevance of Growth Rates 33112.2 Determinants of Growth Rates 33312.2.1 Seedlings 33412.2.2 Saplings 34212.2.3 Adults 34412.2.4 Demographic Significance 34412.2.4.1 Growth Trajectory 34512.2.4.2 Size or Age of Individuals 34512.2.4.3 Above vs Below Ground 34512.2.4.4 Plant Part 34712.2.4.5 Interacting Factors 34712.2.4.6 Experimental Conditions 34812.2.4.7 Individual vs Population Growth 34812.2.4.8 Time and Size 34812.2.4.9 Species 34812.2.5 The Value of Long‐Term Research 34912.3 Modeling Growth 35012.3.1 Insights from Published Data 35112.3.2 Predicting Rates from Environment or Phylogeny 35312.3.3 Deficiencies in Growth Rate Data 35612.4 Conclusions 35712.A Appendix: Growth Rate Data 358References 42813 Fire and Browsers in Savannas: Traits, Interactions, and Continent‐Level Patterns 439Gareth P. Hempson, Sally Archibald, and Carla Staver13.1 Introduction 43913.2 Browser and Fire Attributes 44013.2.1 How do Fire and Browsers Compare as Consumers of Woody Plants? 44013.2.1.1 Frequency and Seasonality 44013.2.1.2 Selectivity, Intensity, and Scale 44013.2.1.3 Elimination Thresholds 44213.2.2 Plant Responses to Fire and Browsing 44213.2.2.1 Defense Traits 44213.2.2.2 Architecture 44313.2.2.3 Resprouting and Bud Protection 44413.2.2.4 Fire‐ and Browser‐Traps 44513.2.2.5 Reproduction and Seedling Recruitment 44613.3 Fire–Browser Interactions 44713.3.1 Consequences of Fire for Browsers 44713.3.1.1 Post‐Fire Environment 44813.3.1.2 Woody Plant Regeneration 44913.3.1.3 Decadal Fire Regimes 45013.3.2 Browser Feedbacks to Fire 45113.3.2.1 Browser Facilitation of Fire 45113.3.2.2 Negative Feedbacks of Mixed‐Feeders 45113.3.3 Fire–Browser Vegetation Impacts 45213.3.3.1 Sapling Escape 45213.3.3.2 Elephant Bark Stripping and Canopy Breakage 45213.4 Biogeography of Fire and Browsing in Africa 45313.4.1 Continental‐Scale Patterns of Fire and Browsing 45513.4.2 Fire–Browser Regimes 45713.4.3 Fine‐ vs Broad‐Leaved Savannas 45713.5 Synthesis 460References 46014 Woody Plant Architecture and Effects on Browsing Herbivores in Savannas 469Tristan Charles‐Dominique, Jean‐Francois Barczi , and Simon Chamaillé‐Jammes14.1 Introduction 46914.2 Factors Limiting Bite Size 47114.3 Factors Limiting Biting Rate 47414.4 Simulating Plant–Herbivore Interactions at the Individual Plant Scale 47614.4.1 Plant Growth Model 47714.4.2 Virtual Browsing and Consequences for Plant Fitness 47814.4.3 Virtual Experiment Set‐up 47814.4.4 Simulation Results 48014.4.4.1 Effect of Leaf Size 48114.4.4.2 Effect of Short Shoots 48114.4.4.3 Effect of Spines 48214.4.4.4 Effect of Cage Architecture 48214.4.4.5 Effect of Short Shoot Induction 48214.4.4.6 Effect of Sprouting 48214.4.5 Significance of Simulation Results 48214.5 Future Directions for Modeling Plant–Herbivore Interactions 483Acknowledgments 48314.A Appendix 484References 48415 Browsing Herbivore–Woody Plant Interactions in Savannas 489Peter Frank Scogings and Juan H. Gowda15.1 Introduction 48915.1.1 The raison d’être 48915.1.2 Approach 49015.2 Feedback Between Woody Individuals and Browsing Herbivores 49215.2.1 Shoot Growth 49215.2.2 Spinescence 49315.2.3 Nutrients and Phenolics 49415.2.4 Is Positive Feedback Widespread? 49515.3 Selective Browsing and Shifts in Woody Vegetation Composition and Structure 49715.3.1 Recruitment and Mortality 49715.3.2 Community Composition and Structure 50015.4 Linking Responses of Woody Individuals and Communities to Functional Traits 50115.5 Future Directions 50415.5.1 Key Gaps 50415.5.2 Standardizing Methods 505References 53916 Mesobrowser Abundance and Effects on Woody Plants in Savannas 551David J. Augustine, Peter Frank Scogings, and Mahesh Sankaran16.1 Introduction55116.2 Mesobrowser Abundance in Savannas 55216.3 Mesobrowser Diets in Savannas 55916.4 Mesobrowser Effects on Woody Plant Communities 56116.4.1 Hluhluwe‐iMfolozi Park, South Africa 56416.4.2 Central Laikipia, Kenya 56516.4.3 Chobe National Park, Botswana 56716.4.4 Kruger National Park, South Africa 56816.5 Evidence from Long‐Term Perspectives 56916.6 The Influence of High Densities of Individual Mesobrowser Species 57016.7 Water, Nutrients, and Mesobrowsers 57116.8 Synthesis 573Acknowledgments 576References 57617 Megabrowser Impacts on Woody Vegetation in Savannas 585Norman Owen‐Smith, Bruce Page, Gabriella Teren, and Dave J. Druce17.1 Introduction 58517.2 Use of Woody Plants Versus Grasses and Other Plant Forms 58617.3 Selection for Size Classes and Woody Plant Parts 58917.4 Plant Damage Imposed and Mortality 59017.5 Plant Species Selected 59217.6 Landscape Transformations Caused by Elephants, Along with Fire 59917.7 A Cautionary Note 60217.8 Overview 602References 60418 Indirect Effects of Browsing Herbivores in Savannas 613Corli Coetsee, Dario Fornara, Antoinette Veldtman, and Benjamin Wigley18.1 Introduction 61318.2 Indirect Effects of Browsers on Other Fauna 61418.2.1 Mammals 61418.2.1.1 Large Herbivore Effects on Rodents 61418.2.1.2 Mesobrowser Effects on Other Herbivores 61518.2.1.3 Megaherbivore Effects on Mesoherbivores 61618.2.1.4 Interactions Among Browsers Where the Type of Browser is Not Apparent 61618.2.1.5 Interactions Among Megaherbivores 61718.2.1.6 Summary 61718.2.2 Birds 61718.2.2.1 Summary 61918.2.3 Reptiles and Amphibians 61918.2.3.1 Summary 61918.2.4 Invertebrates 61918.2.4.1 Summary 62118.3 Effects on Ecosystem Processes 62218.3.1 Carbon Cycling 62218.3.1.1 Consumption of Vegetation by Browsers Affects Ecosystem Carbon Pools 62218.3.1.2 Changes in Litterfall Affect Soil Carbon 62518.3.1.3 Global Change Can Override the Effects of Herbivory on Soil Carbon 62518.3.1.4 Summary 62618.3.2 Soil Nutrient Cycling and Soil Nutrient Pools 62618.3.2.1 Changes in Litter Quality 62618.3.2.2 Herbivore Effects on both Litter Quality and Quantity 62918.3.2.3 Summary 62918.4 Conclusions 629References 630Part IV Synthesis 64319 Water Limitation, Fire, and Savanna Persistence: A Conceptual Model 645Brian Beckage, Gabriela Bucini, Louis J. Gross, William J. Platt, Steven I. Higgins, Norma L. Fowler, Matthew G. Slocum, and Caroline Farrior19.1 Introduction 64519.2 Conceptual Model 64619.2.1 Water Limitation 64819.2.2 Fire 65019.2.3 Fire Feedbacks 65119.2.4 Other Processes 65219.3 Summary 653Acknowledgments 654References 65420 Savanna Ecosystem Models: What Should a Clever Modeler Code? 661Gregory Kiker and Peter Frank Scogings20.1 Introduction 66120.2 Local‐Scale Aspects of Woody Plant–Browser Interactions 66220.3 Model Designs for Plant–Herbivore Interactions 66320.3.1 Plant‐Focused Models 66620.3.2 Herbivore‐Based Models 66820.3.3 Integrated Models: Adding Complexity into Plant–Herbivore Models 67020.4 Discussion 672References 67421 Woody Plants and Large Herbivores in Savannas: Ancient Past – Uncertain Future 683Peter Frank Scogings and Mahesh Sankaran21.1 Introduction 68321.2 Woody Plants 68521.3 Large Herbivores 68821.4 Interactions Between Woody Plants and Browsers 69021.4.1 Adaptations of Woody Plants to Browsing by Mesobrowsers 69021.4.2 Woody Community Responses to Mesobrowsers and Megaherbivores 69221.4.3 Indirect Effects of Browsing 69621.5 Models 69821.5.1 General Conceptual (Qualitative) Models 69821.5.2 Mathematical (Quantitative) Models 70021.6 The Future 701References 703Index 713