Lamto (eBook)

Preface 6
Contents 8
Contributors 18
1 History of the Lamto Ecology Station and Ecological Studies at Lamto 21
1.1 Origin and installation of the station 21
1.2 The scientific programs that sustained the station from 1962 26
1.3 The current programs: 2000 to present 28
1.4 Conclusion: Forty years of scientific production 29
References 29
The Environment 33
2 Geology, Landform, and Soils 34
2.1 Geology 34
2.2 Landform 34
2.3 Soils 36
References 42
3 Climate 44
3.1 Introduction 44
3.2 The Lamto climate in the context of the West African climates 44
3.3 The Lamto Geophysical Station: Forty years of routine climatic observations 46
3.4 Seasonal course of climatic parameters 48
3.5 Interannual variability and temporal trends 56
3.6 Conclusion 59
Acknowledgments 60
References 60
4 Environmental Constraints on Living Organisms 64
4.1 Introduction 64
4.2 Soil water 65
4.3 Soil nutrients 67
4.4 Light 69
4.5 Fire 70
4.6 Herbivory 75
4.7 Conclusion 76
References 76
5 Vegetation 81
5.1 Introduction 81
5.2 Main savanna types 81
5.3 Structure of the vegetation 82
5.4 Life-Forms 87
5.5 Phenological cycles 89
5.6 Conclusion 90
Acknowledgments 90
References 91
Structure and Functioning of Plant Cover 93
6 Soil-Plant-Atmosphere Exchanges 94
6.1 Introduction 94
6.2 Overview of the 1991 to 1994 field campaign 95
6.3 Savanna radiation budget and spectral signatures 97
6.4 Energy budget 103
6.5 Water balance and plant water status 109
6.6 CO2 exchanges and leaf conductance 116
6.7 NO, NO2, and O3 exchanges 121
6.8 Conclusion 123
Acknowledgments 124
References 125
7 Biomass Cycle and Primary Production 131
7.1 Introduction 131
7.2 The aboveground phytomass cycle 131
7.3 The belowground phytomass cycle 140
7.4 Primary production of Lamto savannas 143
7.5 Plant allocation strategies: What can be inferred from phytomass measurements? 150
7.6 Discussion: Toward an integrative approach of primary production and allocation 151
References 152
8 Tree/Grass Interactions 154
8.1 Introduction 154
8.2 Trees alter the understory grass environment 155
8.3 Trees and grasses share the same soil resources 161
8.4 Trees alter grass functioning and production 166
8.5 Conclusion 169
References 172
9 Modeling the Relationships between Vegetation Structure and Functioning, and Modeling Savanna Functioning from Plot to Region 177
9.1 Introduction 177
9.2 Models previously developed for predicting the functioning of Lamto savannas 178
9.3 TREEGRASS: A 3D model for simulating structure- functioning relationships in savanna ecosystems 179
9.4 Modeling the functioning of savannas at large scales 187
9.5 Conclusion 194
Acknowledgments 195
References 195
10 Modification of the Savanna Functioning by Herbivores 198
10.1 Introduction 198
10.2 Herbivore densities, biomasses, and green grass consumption rate in Lamto savannas 198
10.3 Field studies of grazing effect on the savanna functioning 202
10.4 Modeling approaches for understanding grazing effect on the savanna functioning 205
10.5 Conclusion 207
References 209
Carbon Cycle and Soil Organic Matter Dynamics 212
11 Origin, Distribution, and Composition of Soil Organic Matter 213
11.1 Introduction 213
11.2 The inputs of organic matter to soil 214
11.3 Soil organic matter distribution 215
11.4 Chemical composition of soil organic matter 219
11.5 Conclusion 226
References 227
12 Soil Carbon and Organic Matter Dynamics 231
12.1 Soil micro-organisms 231
12.2 The limitation of soil microbial activity by the supply of organic and mineral compounds 232
12.3 Plant litter decomposition 235
12.4 Soil organic matter mineralization and turnover 237
12.5 Modeling organic matter dynamic in Lamto soils 240
12.6 Conclusion 243
References 244
13 Perturbations of Soil Carbon Dynamics by Soil Fauna 247
13.1 Introduction 247
13.2 Earthworms and termites: Abundances and spheres of influence 248
13.3 Carbon distribution and storage 251
13.4 Carbon mineralization 253
13.5 Conclusion 257
References 258
The Nitrogen Cycle 264
14 Nitrogen Inputs to and Outputs from the Soil- Plant System 265
14.1 Introduction 265
14.2 Dry and wet depositions 265
14.3 Biological fixation of atmospheric dinitrogen 268
14.4 Grass cover leaching 273
14.5 Soil leaching 274
14.6 Denitrification 274
14.7 Nitrogen monoxide emission 276
14.8 Impact of fire on the nitrogen cycle 277
14.9 N fluxes associated to grass consumption by animals 280
14.10 Conclusion: The input-output balance of nitrogen 281
References 282
15 Nitrogen Dynamics in the Soil-Plant System 286
15.1 Introduction 286
15.2 Nitrogen dynamics in the shrub-tree layer 286
15.3 Nitrogen dynamics in the grass layer 287
15.4 Annual nitrogen requirements of grasses 291
15.5 Origin of grass nitrogen 292
15.6 The transformations of nitrogen in soil 295
15.7 Conclusion: The savanna, a system that retains nitrogen and mineral nutrients 303
References 305
16 Role of Soil Fauna in Nitrogen Cycling 307
16.1 Introduction 307
16.2 Nitrogen storage and throughput in soil macrofauna and associated structures 307
16.3 Impact of soil macrofauna on nitrogen dynamics and mineralization 311
16.4 Stimulation of plant growth by soil macrofauna 314
16.5 Conclusion 316
References 317
Plant Community Dynamics 320
17 Spatial Pattern, Dynamics, and Reproductive Biology of the Grass Community 321
17.1 Introduction 321
17.2 Structure of the grass layer 321
17.3 Dynamics of the grass layer 329
17.4 Reproduction system of Hyparrhenia diplandra and its population genetic structure as revealed by microsatellites 330
17.5 Conclusion 338
References 338
18 Structure, Long-Term Dynamics, and Demography of the Tree Community 341
18.1 Introduction 341
18.2 Factors influencing tree population dynamics 341
18.3 Spatial patterns of tree species 345
18.4 Tree population dynamics 352
18.5 Discussion: The interaction of demography and spatial patterns and its effect on savanna stability 364
References 366
19 Modeling Tree and Grass Dynamics: From Demographic to Spatially Explicit Models 371
19.1 Introduction 371
19.2 Persistence of savanna species under annual burning: Analysis through matrix population models 372
19.3 Spatialized demographic models 376
19.4 Conclusion: The dynamics of plant populations and spatial patterns 382
References 382
Toward an Integration of Savanna Structure, Functioning, and Dynamics 385
20 A Synthetic Overview of Lamto Savanna Ecology: Importance of Structure- Functioning- Dynamics Relationships 386
20.1 Introduction 386
20.2 Rationales for the structure-functioning-dynamics relationships approach 387
20.3 Structure-functioning relationships as a key to understanding the Lamto productivity paradox 389
20.4 Structure-dynamics relationships as a key to understanding changes in tree/ grass balance 391
20.5 Current approaches for studying tree functioning- dynamics relationships in Lamto savanna 391
20.6 Modeling as a synthesis tool for studying structure- functioning- dynamics relationships 392
20.7 Conclusion 394
References 395
21 Perspectives: From the Lamto Experience to Critical Issues for Savanna Ecology Research 398
21.1 Introduction 398
21.2 Scaling across time 400
21.3 Scaling across space: From plot to landscape and region 402
21.4 Scaling across system complexity 404
21.5 The whole picture: Modeling a spatially organized trophic web and its physical environment 406
21.6 Conclusion 408
References 408
Index 413