Throughfall and Stemflow

Forest canopies affect the amounts of water and nutrients reaching forest soils. Water and nutrient inputs under forest canopies are thus different from those in nearby open areas. Canopies intercept and retain part of the incident precipitation (intercepted water), which is eventually evaporated from the canopy and lost to the atmosphere. Water passing through the canopy can reach the forest floor after dripping from leaves and branches (through-fall) or flowing down the stems of trees (stemflow). The sum of throughfall and stemflow is called net or effective precipitation (Parker 1983). The part of incident precipitation that does not appear on the forest floor by either of these routes is called interception loss. Interception has received special attention in a number of forest hydrology studies using experimental or modelling approaches (e.g. Rutter and Morton 1977; Gash 1979; Massman 1983; Bouten et al. 1996).