MODELING RADIATIVE-TRANSFER AND PHOTOSYNTHESIS IN 3-DIMENSIONAL VEGETATION CANOPIES

A methodology for simulating the three-dimensional radiation regime in laterally heterogeneous vegetation canopies is presented. The method is based on the radiative transfer equation which is a formal statement of radiative energy balance in the configuration space. The transfer equation can be parameterized with models of the leaf area density function, the probability density of leaf normal orientation and the leaf scattering phase function. The transfer equation is numerically solved by the discrete ordinates method - by discretizing the angular variable into a finite number of directions and by introducing finite difference schemes for the spatial derivatives. The method was validated with photosynthetically active radiation (PAR) collected in a poplar stand. A formalism for coupling the predictions of the radiation model with the leaf photosynthetic response function is also presented. The utility of the coupled radiation/photosynthesis model is shown through an investigation of the optimal tree density problem for a given set of canopy architecture data.