Throughfall in a forestry plantation at the La Selva Biological Station, Costa Rica

Throughfall consists of precipitation that falls straight through the vegetation canopy and precipitation that has been intercepted by the vegetation but then drops to the ground. Throughfall is an important and relatively unstudied component of the water budget, especially in tropical forest and agroforest environments where it distributes nutrients from the canopy to the ground, delivers moisture to the land, and contributes to local climate processes. To investigate throughfall in a tropical agroforestry plantation, I sampled throughfall during November and December, 1994, on the Huertos Plantation, located at the La Selva Biological Station in Costa Rica. This research examines the relationships between throughfall and total rainfall, rainfall intensity and duration, and leaf area index values at the Huertos plantation. Total rainfall was most significantly related to throughfall and provided the strongest throughfall predictions. Overall, throughfall accounted for only 54% of total rainfall. Dry conditions between rain events support the importance of evaporation of moisture from vegetative surfaces in accounting for much of the remaining 46%. Two regression models, one representing throughfall as a function of total rainfall and one representing throughfall as a function of total rainfall, rainfall intensity and rainfall duration, demonstrated that throughfall can be accurately predicted on the basis of total rainfall alone.