Transcript VEGETATION CHANGE IN RESPONSE TO FUTURE GLOBAL …

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 –
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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