AN INDIVIDUAL TREE-BASED MODEL OF COMPETITION FOR LIGHT

A Variant of a distance-independent neighborhood model for light compe tition is developed, in which the average amount of light available to an individual tree in a population is found by considering the discre te representations of tree crowns. Trees are assumed to be independent ly and uniformly distributed within a certain area of interaction (a p lot). Tree crowns are considered as either vertical or horizontal plan ar screens (''discrete screens'') of arbitrary form that partially abs orb light and that are illuminated by a point source of light. The ave rage vertical light profile is calculated for both crown representatio ns. The results obtained are discussed and are compared with the descr iption traditionally used in forest modeling; the latter considers a t ree canopy as a ''solid layer'' for which the light profile is calcula ted using Lambert-Beer's law of light absorption. The comparison showe d that the solid-layer approach underestimates the amount of light ava ilable to an individual tree and is less sensitive to changes in the n umber of trees in the plot than the ''discrete screens'' approach. The paper also discusses an application of the results obtained to popula tion-level dynamical models.