Effect of crown shape and tree distribution on the spatial distribution of shade

Abstract

A method for calculating the light extinction probability caused by a forest canopy is presented. With the calculation procedure, it is possible to examine the effect of crown shape, stand density and spatial distribution of trees on the spatial distribution of light extinction probability or on the total shaded area caused by the canopy. At low sun elevations, the momentary projection area of a single crown is greater the more vertically extended the crown is, if the crown volume is held constant. When a longer time period is concerned, the area where the average extinction probability exceeds some arbitrary value is greatest for umbrella-like, horizontally extended crowns. The same is true for a single tree and for a forest stand. When the stand density is low or the tree crown is narrow, the spatial distribution of trees has only a small effect on the amount of shaping; the total amount of shading in random distribution is almost the same as in systematic distribution. In a stand where the total horizontal projection area of crown cones is high, the spatial distribution of trees should be systematic for effective light interception.