An individual tree-based model of competition for light

Abstract

A variant of a distance-independent neighborhood model for light competition is developed, in which the average amount of light available to an individual tree in a population is found by considering the discrete representations of tree crowns. Trees are assumed to be independently and uniformly distributed within a certain area of interaction (a plot). Tree crowns are considered as either vertical or horizontal planar screens (“discrete screens”) of arbitrary form that partially absorb light and that are illuminated by a point source of light. The average vertical light profile is calculated for both crown representations. The results obtained are discussed and are compared with the description traditionally used in forest modeling; the latter considers a tree canopy as a “solid layer” for which the light profile is calculated using Lambert-Beer's law of light absorption. The comparison showed that the solid-layer approach underestimates the amount of light available to an individual tree and is less sensitive to changes in the number of trees in the plot than the “discrete screens” approach. The paper also discusses an application of the results obtained to population-level dynamical models.