Ecosystem Function in Savannas: Measurement and Modeling at Landscape to Global Scales

Contents......Page 6
List of Figures......Page 10
Acknowledgments......Page 22
Introduction......Page 24
Editors......Page 28
Lead Authors......Page 30
Contributors......Page 34
Reviewers......Page 40
Section I: Savannas: Biogeographical and Ecological Perspectives......Page 42
Introduction......Page 44
Concept and Assumptions......Page 46
Spatial Definition of Global Savannas: Ecoregions and Land Cover......Page 49
Vegetation and Biodiversity......Page 55
Climate and Soils of Global Savannas......Page 60
Fire......Page 65
Rural Population, Livestock, and Human Appropriation of Net Primary Productivity......Page 66
Temporal Dynamics......Page 71
Conclusions......Page 73
References......Page 74
Introduction......Page 80
Tree–Grass Coexistence and Determinants of Savanna Structure......Page 81
Savanna Paradigms and Contradictions......Page 82
Savannas, Climate, and Disturbance: A Conceptual Framework......Page 85
Conclusions......Page 90
Acknowledgments......Page 91
References......Page 92
Section II: Carbon, Water and Trace Gas Fluxes in Global Savannas......Page 96
Introduction......Page 98
Site Description and Method......Page 101
Impacts of Fire on NEP......Page 102
Spatial Variability in Savanna Productivity......Page 105
Disturbance Regimes and Carbon Turnover......Page 108
Savanna Productivity under Climate Change......Page 109
References......Page 113
Introduction......Page 118
The Skukuza Flux Tower......Page 119
Eddy Covariance and Environmental Measurements......Page 121
Summary of Earlier Studies at the Skukuza Flux Tower......Page 125
Carbon Flux Characterization at Monthly Time Scales.......Page 126
Results......Page 127
Discussion......Page 133
Acknowledgments......Page 134
References......Page 135
Cerrado Vegetation......Page 138
Influence of Climate and Soils......Page 140
Estimation of Carbon Pools and Carbon and Water Fluxes......Page 142
Leaf Gas Exchange......Page 143
Carbon and Water Fluxes......Page 146
Comparison to Other Tropical Ecosystems......Page 150
Effects of Disturbance on Mass and Energy Exchange......Page 152
References......Page 153
Introduction......Page 158
Site Descriptions......Page 160
Methods......Page 163
Carbon and Water Balance......Page 165
Sensitivity to Precipitation Pulses and Drying Cycles......Page 167
Plant Water Status......Page 168
Conclusion......Page 171
References......Page 172
Introduction......Page 176
Biogeography......Page 178
Leaf and Tree Physiology......Page 179
Canopy Scale: Energy and Water Fluxes......Page 182
Canopy Scale: Carbon Fluxes......Page 184
Discussion......Page 187
References......Page 189
Section III: Remote Sensing of Biophysical and Biochemical Characteristics in Savannas......Page 194
8. Quantifying Carbon in Savannas: The Role of Active Sensors in Measurements of Tree Structure and Biomass......Page 196
Remote Sensing of Savannas......Page 197
Vegetation Structure......Page 198
LiDAR......Page 199
SAR......Page 201
Ground-Based Sensors......Page 202
Vegetation Height......Page 203
Crown and Canopy Descriptors......Page 206
Combined Retrieval of Structural Attributes......Page 207
Above-Ground Biomass......Page 208
Quantifying Changes in Carbon......Page 210
Future Outlook......Page 211
Acknowledgments......Page 212
References......Page 213
Introduction......Page 216
Image Pre-Processing......Page 219
Vegetation Cover Indices......Page 221
Field Calibration and Validation......Page 222
Time Series Woody Extent and FPC Product......Page 224
Ground Cover......Page 226
Woody Change......Page 228
Discussion......Page 229
References......Page 231
Introduction......Page 236
Fractional Cover Mapping......Page 237
LiDAR for Fractional Cover Mapping......Page 240
A New Data Fusion Approach for Fractional Cover Mapping......Page 244
Mapping Canopy Chemistry......Page 247
Conclusions and Research Needs......Page 253
References......Page 254
Introduction......Page 260
Study Area......Page 262
Data......Page 263
Analysis and Modeling......Page 267
Woody Cover Percent and Heterogeneity Maps......Page 268
Woody Cover Explanatory Model......Page 269
Discussion......Page 272
Woody Cover Map......Page 273
Ecological Model......Page 274
Acknowledgments......Page 275
References......Page 276
Introduction......Page 280
Active Fire Detection......Page 283
Burned Area Detection......Page 285
Fire Characterization......Page 288
Summary......Page 290
References......Page 291
Section IV: Perspectives on Patch- to Landscape-Scale Savanna Processes and Modeling......Page 296
Introduction......Page 298
Niche Separation......Page 299
Disturbance......Page 301
Facilitation......Page 304
An Environmental Framework for Tree–Grass Coexistence......Page 305
Future Avenues for Research......Page 307
References......Page 309
Introduction......Page 314
Evidence for the Importance of Space in Savannas......Page 317
Spatial Modeling Approaches......Page 319
Conceptual Models......Page 320
Remote Sensing, GIS, and Spatial Statistics......Page 322
Moment Equations......Page 323
Cellular Automata......Page 324
Grid-Based Models......Page 325
Conclusions......Page 327
References......Page 328
Introduction......Page 334
Modeling Savanna Dynamics in Australia: The Flames Model......Page 336
Methods......Page 339
Results......Page 340
Discussion......Page 345
References......Page 347
Introduction......Page 350
An Ecohydrological Model......Page 352
Scenario Analysis Using the Model......Page 353
Impacts of Land Use and Climate Change on Population Dynamics......Page 355
The Road Ahead: Upscaling Ecological Processes in Space......Page 357
Conclusion......Page 361
References......Page 362
Section V: Regional Carbon Dynamics in Savanna Systems: Remote Sensing and Modeling Applications......Page 366
Introduction......Page 368
Climate and Disturbance Controls......Page 369
Analytical Framework......Page 371
Geographic Variation in Emergent Limitations......Page 373
Teleconnections to Climate Indices......Page 375
Contrasting the Sudanian and Tanzanian or Southeast African Regions......Page 377
Ecoclimatic Controls on Coupling to Climate Oscillations......Page 380
Continuing Study and Emerging Opportunities......Page 382
References......Page 383
Introduction......Page 388
Model Structure......Page 390
Forcing Data: Normalized Difference Vegetation Index......Page 391
Model Parameterization and Forward Modeling......Page 392
Timescales of Carbon Fluxes......Page 393
Parameter Values and Uncertainties......Page 394
Savanna Fires......Page 395
Dynamics of Savanna Carbon Fluxes......Page 398
Lag Anomaly Correlations of NEP and NBP......Page 399
Impulse–Response Analysis......Page 401
Summary......Page 402
References......Page 403
Appendix......Page 406
Introduction: The Cerrado Region......Page 408
Land Use Patterns and Processes......Page 409
Carbon Stocks and Fluxes......Page 411
Impacts of Fire on C Budget......Page 412
Impacts of Conversion......Page 414
Occupation Trends and Future Scenarios......Page 416
Concluding Remarks......Page 417
References......Page 418
Introduction......Page 424
Background and Study Area......Page 426
Land Cover and Land Use Changes......Page 429
Predictive Model of the Expansion of the Agricultural Frontier in the Llanos, 2007–2020......Page 432
Calculations of Carbon Emissions......Page 433
Observed 1970–2007 and Predicted 2010–2020 Land Cover Changes......Page 434
Trends in C Emissions for 2020 from Land Use Changes in Cattle Grazing and Plantations......Page 435
Discussion......Page 437
Acknowledgments......Page 440
References......Page 441
21. Modeling Vegetation, Carbon, and Nutrient Dynamics in the Savanna Woodlands of Australia with the AussieGRASS Model......Page 444
Introduction......Page 445
Model-Driving Data Variables......Page 446
Grazing Pressure......Page 448
Improving the Modeling of Surface Cover......Page 449
Calibrating Mass to Cover Algorithms......Page 450
Carbon and Nitrogen Stocks......Page 454
Case Study: Broad Scale Sensitivity of Natural Resource Attributes to Stocking Rates......Page 455
Impacts of Current Fire and Stocking Rate Regimes......Page 456
Broad Scale Sensitivity of C and N Fluxes with Changing Grazing Pressure and Fire......Page 459
Conclusion......Page 460
References......Page 461
Section VI: Continental and Global Scale Modeling of Savannas......Page 464
Introduction......Page 466
Background on Carbon Modeling and Remote Sensing Methods......Page 467
Predictions of Savanna NPP and Biomass Carbon Pools......Page 471
Global Climate Controls on Savanna Vegetation Dynamics......Page 473
Discussion of Possible Futures for Savanna Ecosystems......Page 478
References......Page 479
Introduction......Page 484
Savanna Models......Page 485
SAVANNA-CENTURY Model Description......Page 487
Model Testing and Calibration......Page 490
Model Results......Page 492
Discussion......Page 496
References......Page 500
Introduction......Page 504
Dynamic Vegetation Models for Use in Savannas......Page 506
Tree to Grass Ratio as Affected by Mean Annual Precipitation, Fire Return Interval, and Variable Rooting Depths......Page 507
Interactive Effects of Precipitation and NPP......Page 510
Dynamic Simulation of Wildfires......Page 514
Summary......Page 516
References......Page 517
Section VII: Understanding Savannas as Coupled Human-Natural Systems......Page 520
Introduction......Page 522
Savannas as Coupled Human–Environment Systems......Page 523
Land Use, Drivers, and Processes of Change in Savannas......Page 524
Transitions: Consequences of Change for People......Page 528
Sustainable Savannas......Page 530
Acknowledgment......Page 532
References......Page 533
Introduction......Page 538
Society–Nature Relationships in Savanna Environments......Page 539
Socioecological Models and Modes of Causal Inference......Page 540
Conceptualizations of Socioecological Relations......Page 542
Savanna Land-Use Ecology......Page 543
Social Depth of Causal Chains......Page 545
Case: Social Factors Influencing Grazing Patterns in Tropical Savannas......Page 547
Conclusions......Page 549
References......Page 550
Section VIII: Synthesis......Page 554
Introduction......Page 556
Legacy Research: Coarse Resolution, Time-Series Remote Sensing, and Savannas......Page 557
Biogeographical and Ecological Perspectives......Page 558
Carbon, Water, and Trace Gas Fluxes......Page 560
Remote Sensing......Page 565
Landscape Modeling......Page 568
Regional and Continental Scale Modeling and Applications......Page 572
Interactions between Humans and Savanna Systems......Page 576
The Key Needs for an Ecology-Model-Remote Sensing Synthesis......Page 578
References......Page 581