9407853 Herwitz Height differences of neighboring canopy tree crowns are responsible for the characteristic roughness of tropical rainforest canopies. If the three-dimensional form of such a canopy was known, the differential interception of direct solar radiation by the more prominent canopy trees and the lateral shading of their less prominent neighbors could be determined. Crown asymmetry, which increases canopy tree susceptibility to windthrow and toppling because of the crown's uneven weight distribution is believed to be the best result of lateral shading. The objective of proposed study is to test the hypothesis that differential interception of solar radiation has a predictable influence on the long-term survivorship and growth patterns of tropical rainforest canopy trees. This hypothesis will be tested by: (1) three-dimensional modeling of a tropical rainforest canopy in Queensland, Australia using data derived from large-scale aerial stereophotographs taken in July 1976; (2) determining the annual daily courses of solar radiation for the selected site; (3) applying a 3-D model to simulate light interception over the course of a year; (4) computing the light-intercepting crown area/total crown area; (5) using the direct solar radiation model survivorship probabilities and growth potential; and (6) analyzing the predicted compared with actual derived from large-scale aerial steropairs to be taken in a proposed overflight sequence in July 1994. To our knowledge, no study has previously examined tropical rainforest canopy dynamics over a comparable time period with the same resolution that will be obtained using our proposed combination of large-scale aerial photogrammetry and computer modeling. Identification of some of the factors contributing to the spatial patterns of mortality, survivorship, and growth of neighboring plants competing for sunlight will allow a clearer understanding of the interactions among canopy trees and more accurate models of carbon and water exchanges i n tropical rainforests.
