Scientific Colloquium
March 19, 2004

Plant canopies are complex entities, possessing structural and functional
heterogeneity in the vertical and horizontal dimensions.  This complex,
however, is not static.  Many structural and functional attributes of a
plant canopy, such as leaf area index and photosynthetic capacity, can vary
in time due to phenology, weather, soil moisture, stand age and acclimation.

In this talk, we use a biophysical model, CANVEG/CANOAK, and eddy flux
measurements from the FLUXNET project to explore how spatial and temporal
variations in canopy structure and function translate into fluxes of carbon
dioxide, water vapor and energy between forests and the atmosphere.

The CANVEG model contains coupled micrometeorological and physiological
modules for the plant and soil compartments.  The micrometeorological models
compute leaf and soil energy exchange, turbulent diffusion, scalar
concentration profiles and radiative transfer through the canopy at hourly
time steps.  Environmental variables, computed with the micrometeorological
module, in turn, drive the physiological models that compute leaf
photosynthesis, stomatal conductance, transpiration, leaf, bole and
soil/root respiration.  We use the complex model, in combination with field
measurements, to evaluate when simpler models can be used and forced with
remote sensing information to understand the 'breathing' of the biosphere.