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ECOSYSTEM STRUCTURE AND FUNCTION
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ECOSYSTEM STRUCTURE AND FUNCTION

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  1. 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

  2. HOW DO WE STUDY AND DEFINEECOSYSTEM STRUCTURE? – I • Much of ecosystem structure can be inferred from vegetation structure: Plants  Consumers (fauna)  Decomposer fauna and flora  Soil structure (Ricklefs)

  3. HOW DO WE STUDY AND DEFINEECOSYSTEM 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)

  4. Tropical Rain Forest with Broadleaf Rain-Evergreen Trees Tropical Savanna with Drought-Deciduous Trees and C4 Grasses HOW DO WE STUDY AND DEFINEECOSYSTEM STRUCTURE? – III • Functional aspects of vegetation in definition • Leafduration – Evergreen, winter or drought deciduous • Leafshape/size – Broadleaf, needleleaf • Photosyntheticpathway: for Grasses (C3, C4) (profile/photo from Walter, 1985)

  5. WHY IMPORTANT? – ROLE OF VEGETATION STRUCTURE IN THE EARTH SYSTEM – I • FUNCTION FOLLOWS STRUCTURE: • Biophysicalprocesses vary with vegetation type ATMOSPHERE-BIOSPHERE EXCHANGE  • MATTER – H2O (Transpiration) • ENERGY – SOLAR ABSORPTION, HEATING REGIONAL AND GLOBAL CLIMATE (Mackenzie 1998)

  6. 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

  7. WHY IMPORTANT? – ROLE OF VEGETATION STRUCTURE IN THE EARTH SYSTEM – III • Vegetation structure affects wildlifehabitat • Food, shelter • Vegetation complexity  Habitat complexity • Vegetation and human society – • Managed vs. unmanaged uses • Shelter – Wood, fiber • Food – Grazing, crops, secondary forest products • Watershedmanagement • Aesthetic, cultural values

  8. WHAT FACTORS CONTROL VEGETATION DISTRIBUTION? – I FIVE KEY FACTORS: • REGIONALCLIMATE – 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.)

  9. WHAT FACTORS CONTROL VEGETATION DISTRIBUTION? – II FIVE KEY FACTORS (con’t): • REGIONALCLIMATE – Broad patterns of: • Physical Climate • Seasonalthermal, moisture, and light regime • Climatevariability and directional change • Chemical Climate • Atmospheric CO2 concentration – fertilization effect • Acid rain • N deposition – fertilization effect

  10. 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)

  11. DRIVERS OF FUTURE ECOLOGICAL CHANGE: MULTIPLE FACTORS • Climatechange – 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 • Fertilizationeffects: • CO2 • N deposition