A FRACTAL-BASED POPULUS CANOPY STRUCTURE MODEL FOR THE CALCULATION OF LIGHT INTERCEPTION

A canopy light-interception model for a Populus stand is presented. To model the canopy, a new approach based on fractal geometry is used, which allows the simulation of the three-dimensional (3D) radiation regime in a heterogeneous canopy. Based on both the fractal approach and a set of growth and development rules of Populus trees grown under short-rotation intensive culture, a 3D crown architecture submodel is developed to generate the individual tree frames of a stand. The temporal and spatial variations in leaf area are taken into account in a leaf dynamics submodel. Coupling of the leaf model with the tree frame model results in a 3D leaf distribution in the canopy. Diffuse and direct light distribution are computed for each leaf layer using a 3D radiative transfer model. The intercepted light of sunlit and shaded leaves in each layer is summed to find the instantaneous light interception by the canopy. The daily and seasonal total canopy light interception are estimated using the Gaussian numerical integration over the daylight period and the growing season, respectively.