ECOSYSTEM STRUCTURE AND FUNCTION

How do we define ecosystem structure Importance of ecosystem structureFactors controlling ecosystem structureDrivers of future ecological change

©2001 T. Kittel, NCAR

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)

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)

HOW DO WE STUDY AND DEFINEECOSYSTEM 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)

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