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ECOSYSTEM STRUCTURE AND FUNCTION How do we define ecosystem structure Importance of ecosystem structure Factors controlling ecosystem structure Drivers of future ecological change ©2001 T. Kittel, NCAR HOW DO WE STUDY AND DEFINE ECOSYSTEM STRUCTURE? – I Much of ecosystem structure can be inferred from vegetation structure: Plants Consumers (fauna) Decomposer fauna and flora Soil structure (Ricklefs) HOW DO WE STUDY AND DEFINE ECOSYSTEM STRUCTURE? – II Vegetation structure defined by dominant plants: – By dominance and density of trees, shrubs, grasses – Forest woodland savanna grassland Shrubland shrubsteppe grassland SAVANNA GRASSLAND (profiles from Walter, 1985) HOW DO WE STUDY AND DEFINE ECOSYSTEM STRUCTURE? – III Functional aspects of vegetation in definition • Leaf duration – Evergreen, winter or drought deciduous • Leaf shape/size – Broadleaf, needleleaf • Photosynthetic pathway: for Grasses (C3, C4) Tropical Rain Forest with Broadleaf Rain-Evergreen Trees (profile/photo from Walter, 1985) Tropical Savanna with Drought-Deciduous Trees and C4 Grasses WHY IMPORTANT? – ROLE OF VEGETATION STRUCTURE IN THE EARTH SYSTEM – I FUNCTION FOLLOWS STRUCTURE: • Biophysical processes vary with vegetation type ATMOSPHERE-BIOSPHERE EXCHANGE MATTER – H2O (Transpiration) ENERGY – SOLAR ABSORPTION, HEATING REGIONAL AND GLOBAL CLIMATE (Mackenzie 1998) WHY IMPORTANT? – ROLE OF VEGETATION STRUCTURE IN THE EARTH SYSTEM – II • Vegetation type affects biogeochemical processes e.g., Global C and N Cycles NET PRIMARY PRODUCTION – C assimilation, N uptake PLANT C, N INPUTS TO SOIL DECOMPOSITION RATES TERRESTRIAL C, N FLUXES TO THE ATMOSPHERE RADIATIVELY-ACTIVE TRACE GASES GLOBAL CLIMATE WHY IMPORTANT? – ROLE OF VEGETATION STRUCTURE IN THE EARTH SYSTEM – III • Vegetation structure affects wildlife habitat Food, shelter Vegetation complexity Habitat complexity • Vegetation and human society – Managed vs. unmanaged uses Shelter – Wood, fiber Food – Grazing, crops, secondary forest products Watershed management Aesthetic, cultural values WHAT FACTORS CONTROL VEGETATION DISTRIBUTION? – I FIVE KEY FACTORS: REGIONAL CLIMATE – Broad patterns TOPOGRAPHY – Slope, aspect, exposure BEDROCK – Soil parent material, soil genesis BIOTA – Competition, herbivory, biotic disturbance (insect outbreaks, human) TIME – Succession, disturbance (fire, etc.) WHAT FACTORS CONTROL VEGETATION DISTRIBUTION? – II FIVE KEY FACTORS (con’t): REGIONAL CLIMATE – Broad patterns of: • Physical Climate Seasonal thermal, moisture, and light regime Climate variability and directional change • Chemical Climate Atmospheric CO2 concentration – fertilization effect Acid rain N deposition – fertilization effect WHAT FACTORS CONTROL VEGETATION DISTRIBUTION? – III Scale determines relative importance of controls: • GLOBAL/CONTINENTAL – Broad patterns of climate determines biome to ecoregional vegetation • LANDSCAPE/LOCAL – Microclimate, geomorphology, soils, time, grazers, human activity e.g., Conifer forests, Colorado Front Range (Walter 1985) (Neilson et al. 1998) DRIVERS OF FUTURE ECOLOGICAL CHANGE: MULTIPLE FACTORS Climate change – Anthropogenic forcings: • Greenhouse gas emissions (GHG): CO2, CH4, etc • Sulfate aerosols (SUL), Cloud condensation nuclei, .. • Landuse change Surface biophysical properties Disturbance – Landuse change: • Deforestation, cropland conversion • Overgrazing, desertification • Species invasions Fertilization effects: • CO2 • N deposition