PREDICTING SPATIAL-DISTRIBUTION OF DIRECT-RADIATION BELOW FOREST CANOPIES

The study explores the effects of latitude, crown shape, stand density and tree arrangement on the horizontal variation of daily irradiance at different depths in the stand. There was a continuous decrease in the horizontal variance of irradiance in Poisson stands, but in hexagonally arranged stands, local minima appeared in the variance profile. At low latitudes with broad crowns there was only one local minimum. With increasing latitude and crown height to crown width ratio, the number of minima increased to two or three, but the minima were less prominent. The results are discussed with reference to the hypothesis that horizontal variance of irradiance regulates the height of understory trees and canopy layering.