The Kuala Belalong plot is set up as part of a long term research programme of the Kuala Belalong Field Studies Centre, Universiti Brunei Darussalam. The Centre, located in the Batu Apoi Forest Reserve, Temburong, was used as the base of a 15-month joint UBD-RGS Brunei Rainforest Project/Expedition in 1991-92.
The topography of the Batu Apoi Forest Reserve is steep and sharp. The landscape rises from about 30 m above sea level at Kuala Belalong, to 1850 m at Gunung Pagon in the extreme southern part of the Reserve, entirely composed of deep V-shaped valleys separated by sharp, knife-edge ridges. The geology of the Reserve consists of sedimentary rocks predominantly of shales of the Setap Formation. On ridgetops and summits, the shale is overlaid by the Meligan formation. The soils are silty clay dominated by quartz and kaolinite, also high in iron and aluminium oxides but extremely low in plant nutrients (N & P) and basic nutrients (Ca, Mg).
The plot is laid out on the ridge west of the Centre, in primary, mixed dipterocarp forest at about 160-320 m elevation. The plot includes both ridge top and steep hill side habitats. Earlier study of a hectare plot in the same area showed the presence of 550 trees and 231 species, making it among the most species-rich plot recorded in Northern Borneo for trees ≥ 10 cm dbh in one hectare of mixed dipterocarp forest. The establishment of the 25ha plot is sponsored by HSBC, Brunei Darussalam.