The effect of leaf clustering in the interception of light in vegetal canopies: theoretical considerations

The degree of aggregation or clumping of leaves was often considered to have a significant effect on transmission of light by a plant canopy. We produced simulated distributions of leaves, represented by small circles, with degrees of aggregation varying from random to a strongly clumped distribution. We calculated the interception of every leaf using different lines to represent light beams, pointing from the origin to different directions: every 5 degrees in azimuth and elevation. The percentage of lines not intercepting any leaf was considered as the transmittance of light. The simulations considered two factors: leaf area index (LAI) (from 1 to 9) and degree of aggregation (from random to 100%). The results for a random distribution fit the predictions of the negative exponential function. A degree of clumping of 20% produced significant differences with respect to the predictions of the negative exponential function. The relationship between relative variance (rv) of the leaves' distribution and degree of clustering is largely independent of LAI for values ranging from 3 to 7. We suggest that result could be used as a method to estimate the degree of clumping of real canopies, through the analysis of hemispherical images. (C) 1999 Elsevier Science B.V. All rights reserved.