Association between Soil Moisture Gradient and Tree Distribution in Lowland Dipterocarp Forest at Pasoh, Malaysia
A study was conducted on soil moisture in Pasoh 50-ha demography plot, Pasoh Forest Reserve, Negeri Sembilan, Malaysia to assess the variations of moisture content for different soil types and depths and the association between soil moisture and tree community. The soil types examined were dry alluvial (DA), wet alluvial (WA), and ridge areas (RD). Soil moisture was measured at 15, 30, 45, 60, and 75 cm depths using AquaPro Frequency Domain Reflectometry (FDR) system. The average monthly soil moisture measurement for a two-year period varied between soil types with 48% for dry alluvial soils, 56% for ridge soils, and 68% for wet alluvial soils. However, maximum moisture was recorded for wet alluvial soils at 100%, followed by ridge soils at 92% and dry alluvial soils at 80%. Wet alluvial soils showed highest soil moisture at all soil depths. Soil moisture increased with increasing soil depth with moistures at 75 cm depth being significantly different from moisture at other depths. Though soil moisture increased with soil depth, the difference was only significant at 75 cm depth. The species distribution based on soil types in the Pasoh 50-ha demography plot showed that Euphorbiaceae, Lecythindaceae, Myrtaceae, and Sapidaceae were abundant at wet alluvial soil. At SA, the abundant species were Annonaceae, Myrsinaceae, and Clusiaceae, while Burseraceae, Alanggiaceae, Ansiophylleaceae, Fabaceae, Ulmaceae, and Sterculiaceae were abundant at RD. This indicates that species abundance at the Pasoh 50-ha demography is associated with site condition.