Soil Physical Properties and Preferential Flow Pathways in Tropical Rain Forest, Bukit Tarek, Peninsular Malaysia

Abstract

Soil physical properties and water movement within soil were investigated using dyes in a tropical rain forest, the Bukit Tarek Experimental Watershed of Peninsular Malaysia. The saturated hydraulic conductivity (Ks) decreased with increasing soil depth. The Ks values were higher than those reported for other tropical soils. The geometric means of the Ks values ranged from 4.69×10−3 (80 cm) to 4.07×10−2 cm s−1 (10cm). This suggests saturation overland flow may not be dominant but that subsurface flow must play an important role in stormflow generation. The shapes of the soil moisture characteristic curves resembled those of forest soils which have large changes in volumetric water content at pressure heads <30 cmH2O. The relatively high conductivities were due to the presence of a porous zone of decomposed root channels which existed continuously in vertical direction. Besides decayed roots, living roots also encourage preferential flow in vertical and lateral (downslope) directions. Termite activities may also form water flow pathways in tropical regions. These detailed results help us analyze water flow within the soil in tropical rain forests.