Topographic Analysis of a Large-scale Research Plot in Seasonal Dry Evergreen Forest at Huai Kha Khaeng Wildlife Sanctuary, Thailand.

Abstract

For the rehabilitation of the degraded and abandoned land in the tropical area, it needs to define the various characteristics of remaining natural forests. This work was done to find out a physical hazard for root elongation of plant at Lambir Hills National Park, Miri, Sarawak, Malaysia, with special reference to soil hardness and soil texture. Furthermore, soil moisture and soil temperature were monitored at the hill ridge and at the valley to show their annual fluctuation. Soil physico-chemical properties at the hill ridge and the valley were also investigated. At the hill ridge, well-developed soils with a deep solum were found. Organic matter content was high only at the surface horizon (0-5 cm) where a root mat develops. Although soil moisture content fluctuated significantly, the soil was dry throughout the monitoring period. On the other hand, at the valley, soil moisture content was relatively stable even after the frequent rainfall. The small particles and nutrients at the valley have been brought by the continuous water and eroded particles supply from surroundings. Based on the topographical investigation, the study area was roughly divided into 3 categories: 1) Steep slope area : Soil and vegetation status may be often affected and modified by the land slide or soil erosion. Soil texture was sandy loam, loamy sand, or loam. Gravelly materials often appeared in the subsurface layer at the depth of 20-40 cm, which are hard for root to penetrate into. This layer can be regarded as the one with physical hazard against root penetration. 2) Gentle slope area : Soil and vegetation status are relatively stable for a long time. Soil texture was light clay or heavy clay. Transported clayey materials were accumulated to a depth below 20 cm, and/or the in-situ weathering in the deeper part could have occurred because of the relatively stable topography. 3) Ridge area : Although soil and vegetation status looks stable in view of topography, moisture condition much fluctuated. Soil texture was clay loam or sandy clay loam, which was the middle range between that of a steep slope area and a gentle slope area. The physical hazard in the soil might not be found, but the rates of root elongation and plant growth may be slow since the soil is prone to be dry.