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.