The research site, Pasoh Forest Reserve is a typical lowland rain forest in Peninsular Malaysia. All of the study was conducted in the Pasoh Forest Reserve in Negeri Sembilan state (latitude 2°59' N, longitude 102°19' E, altitude 75-150 m). The total area of the reserve is 2450 ha, surrounded in three directions (east, south and west) by oil palm plantations and to the north adjacent to virgin hill dipterocarp forests. The core area of the forest (approximately 600 ha), where the study plots were located, is generally homogenous in topography and community structure, with no evidence of major human disturbance. The core area is surrounded by regenerating forests which were logged in the early 1950s and the remaining canopy trees in this forest presently reach 30 to 40 m in height. The parent materials of the soils in the reserve area consist mainly of shale, granite, and fluviatile granitic alluvium. The density of the emergent trees in the regenerating forest is much less than that in the core area of the reserve. The forest contains stands at various stages of maturity from canopy gaps to climax forests topped by emergent trees with heights of 50 to 60 m. Gaps are common from place to place in the forest.
Some meteorological data for the Pasoh Forest Reserve are available. It has been reported that there are two weak dry seasons (July and January) in the area in a year. Annual rainfall varied from 1728 to 3112 mm year-1 during 1970 and 1974 (Manokaran and Swaine 1994). The mean monthly relative humidity in the forest ranges from 70% to 100% during wetter months, and from 80% to 93% during the drier months. The average day temperature in Peninsular Malaysia is between 26.7℃ and 35.0℃ while night temperature is between 21.1℃ and 23.9℃.
The main part of the reserve consists of a lowland dipterocarp forest of the Keruing-Meranti type. Within an area of the 50 ha, a total of 335,256 stems with 1 cm DBH (Diameter at Breast Height) and above belonging to 814 species, 294 genera and 78 families have been recorded. The most common plant families are Euphorbiaceae and Annonaceae among understory species, and Dipterocarpaceae, Leguminosae and Burseraceae among canopy species. For trees above 30 cm DBH, the most abundant species is Shorea leprosula (Dipterocarpaceae).