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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
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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)
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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 SAVANNAGRASSLAND (profiles from Walter, 1985)
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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 Savanna with Drought-Deciduous Trees and C4 Grasses Tropical Rain Forest with Broadleaf Rain-Evergreen Trees (profile/photo from Walter, 1985)
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WHY IMPORTANT? – ROLE OF VEGETATION STRUCTURE IN THE EARTH SYSTEM – I +FUNCTION FOLLOWS STRUCTURE: Biophysical processes vary with vegetation type ATMOSPHERE-BIOSPHERE EXCHANGE MATTER – H 2 O (Transpiration) ENERGY – SOLAR ABSORPTION, HEATING REGIONAL AND GLOBAL CLIMATE (Mackenzie 1998)
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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
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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
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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.)
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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 CO 2 concentration – fertilization effect Acid rain N deposition – fertilization effect
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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)
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DRIVERS OF FUTURE ECOLOGICAL CHANGE: MULTIPLE FACTORS +Climate change – Anthropogenic forcings: Greenhouse gas emissions (GHG): CO 2, CH 4, etc Sulfate aerosols (SUL), Cloud condensation nuclei,.. Landuse change Surface biophysical properties +Disturbance – Landuse change: Deforestation, cropland conversion Overgrazing, desertification Species invasions +Fertilization effects: CO 2 N deposition
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