Soil and Belowground Characteristics of Pasoh Forest Reserve

Abstract

We describe the soil and belowground characteristics of the Pasoh Forest Reserve (Pasoh FR), Peninsular Malaysia. Soil survey was conducted using the Malaysian classification system in primary and regenerating forests of Pasoh FR. The physical and chemical properties of various soil horizons were measured at the selected soil pits. Soil N dynamics as a soil biological process was also studied in a range of forest environments, including gap and closed forest. The fine root biomass in the topsoil was also quantified in primary forest. Pasoh FR has at least 18 soil types. The soils of Pasoh FR are whitish to yellowish in color rather than reddish. When compared to the other Southeast Asian tropical forest soils, the particle size distribution is characterized by lower sand and higher silt contents. Chemically, the Pasoh FR soil accumulates greater amounts of Al. Most CEC (cation exchange capacity) are occupied by Al. The high Al content leads to lower P availability. The pool of inorganic N at 0--10 cm soil depth ranges from 14.8 to 23.9 {\textmu}gg N g-1. Net N mineralization rate in topsoil in the primary forest is estimated to be 100 kgN ha-1 yr-1. Nitrification is pronounced at uppermost layer. The fine root biomass (FRB) less than 2,3 and 5 mm in diameter (d) are 624, 751, 970 g m-2, respectively. Within the top 20 cm, the FRB (< 1 mm in d) constitutes 73% of the total FRB (< 5 mm in d) from 0--4 cm and about 40% in subsequent layers. The Pasoh FR soil is supposed to be infertile. Net N mineralization is observed mainly in the topsoil. These facts suggest that the FRB (< 2 mm in d) constitutes a major part of the total, especially in the top soil to effectively absorb mineral nutrients released from decomposing organic matter.