A FRACTAL-BASED POPULUS CANOPY STRUCTURE MODEL FOR THE CALCULATION OFLIGHT 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, w hich allows the simulation of the three-dimensional (3D) radiation reg ime in a heterogeneous canopy. Based on both the fractal approach and a set of growth and development rules of Populus trees grown under sho rt-rotation intensive culture, a 3D crown architecture submodel is dev eloped 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 mode l results in a 3D leaf distribution in the canopy. Diffuse and direct light distribution are computed for each leaf layer using a 3D radiati ve transfer model. The intercepted light of sunlit and shaded leaves i n each layer is summed to find the instantaneous light interception by the canopy. The daily and seasonal total canopy light interception ar e estimated using the Gaussian numerical integration over the daylight period and the growing season, respectively.