SPATIAL VARIABILITY IN THE INTERCEPTION OF INCLINED RAINFALL BY A TROPICAL RAINFOREST CANOPY

Many epiphytes in forest canopies are drought-adapted due to the limited water-holding capacity of the aboveground woody surfaces that support them. The objective of our study was to evaluate whether neighboring tropical rainforest canopy trees differentially intercept inclined rainfall, and discuss the possible effects on epiphyte distribution patterns. The study involved: (1) developing a computer model representing the 3-D geometry of a tropical rainforest canopy surface in northeast Queensland, Australia, using photogrammetric crown elevation data and a geographic information system; (2) generating a shaded canopy relief image to compute the effective rainfall-intercepting crown areas of 50 selected canopy trees during a single precipitation event; and (3) analyzing the relationships between the selected trees' effective crown areas and the net rainfall totals measured beneath their crowns. A significant correlation between the effective crown areas and net rainfall totals indicated that the inclined rainfall was differentially intercepted, with the more prominent canopy trees creating rainshadows on less prominent neighboring canopy trees. It has been generally assumed that the vertically projected crown areas of canopy trees intercept the same depth equivalent of precipitation. The results of our study suggest that rainforest canopy trees in the cyclone-prone tropics do not receive the same depth equivalents of mean annual rainfall. We conclude that the differential interception of rainfall may influence the spatial pattern of water availability and thus the distribution of epiphytes in a forest canopy. Muchas epífitas que crecen en las bóvedas arbóreas de los bosques tropicales húmedos están adaptadas a la sequía debido a que las cortezas que las sostienen por encima del suelo ofrecen muy baja capacidad de retención de agua. La meta de nuestro estudio consistió en analizar si en estos bosques, las bóvedas de los árboles vecinos interceptaban en forma diferencial el agua de lluvia que cae en ángulo para, enseguida, evaluar los efectos que esto pudiese tener en las pautas de distribución de las epífitas. En el estudio se incluyó lo siguiente: (1) el desarrollo de un modelo informático en el que figura la representación tridimensional de la superficie de una bóveda arbórea en un bosque tropical húmedo del noreste de Queensland, Australia. Esto se hizo en base a datos sobre la elevación de la corona arbórea obtenidos mediante fotogrametría, junto con un