Modeling the gap probability of a discontinuous vegetation canopy

A model is presented for the gap probability of a discontinuous vegetation canopy, such as forest, savanna, or shrubland. The case in which the distribution of individual canopy sizes and shapes is known and individual canopies are randomly distributed but do not overlap, and the case in which the canopies to intersect and/or overlap such that foliage density remains constant with the overlap area are both considered, although an exact solution is provided only for the latter. A comparison of modeled gap probabilities with observed gap probabilities for a Maryland (US) pine stand (as taken from the literature) shows good agreement for zenith angles of illumination up to about 45°. Above 45°, the fit worsens, presumably because the horizontal branch structure of the pine canopy is less attenuating as the illumination angle approaches the horizon