THROUGHFALL, STEMFLOW, OVERLAND-FLOW AND THROUGHFLOW IN THE ULU SEGAMA RAIN-FOREST, SABAH, MALAYSIA

On an annual basis 80.7% of the 3627 mm precipitation at a site of the East Ridge at Danum Valley, September 1989 to September 1990, reached the forest floor as throughfall and 1.9% as stemflow, giving an interception loss of 17.4%. The proportion of total rainfall intercepted decreases with storm magnitude. Stemflow amounts vary greatly from tree to tree. Under forest, removal of the ground cover and understorey vegetation led to changes in runoff and soil loss; soil faunal activity under natural forest produced higher soil loss from undisturbed natural plots, than from adjacent, partly cleared plots. Between 2.0 and 2.5% of the rain reaching the ground forms overland flow, the remainder infiltrates and much may be evacuated by pipeflow. Storms of 35 mm or more, which accounted for less than 35% of all rain events, produced 70% of the runoff and soil loss.