Canopy processes: implications for transpiration, interception and splash induced erosion, ultimately for forest management and water resources
摘要
Some recent experimental and theoretical developments in research related to tropical forest canopies are reviewed. Deuterium tracing studies in India, which rely on the collection of samples of transpired water from leaves in the canopy, have established the importance of tree size as an index of whole tree transpiration and the use of leaf area, basal area and sapwood area for scaling transpiration from the tree to plot scale is discussed.Experimental studies of the interception loss from tropical trees in Indonesia, India and Sri Lanka have established that conventional interception models of the Rutter type, although adequate for use in temperate climates, are entirely inappropriate for use in the tropics. It is now recognised that the failure of this approach is due to neglect of the process of drop size dependent canopy wetting. The use of rainfall simulators and optical disdrometers in the tropics has demonstrated that to achieve the same degree of canopy wetting upwards of ten times the depth of rainfall may be required for high intensity tropical storms (with large drop sizes) as compared with low intensity, frontal rainfall systems, common in temperate climates. Rainfall simulator studies have also demonstrated that the final degree of wetting is also reduced when vegetation is wetted with drops of large size. These studies have also demonstrated that the drop size of secondary drops falling from vegetation is dependent on the vegetation type and is very much greater for large leafed species such as Tectona grandis as compared with species such as Pinus caribaea with smaller needle formed leaves.