Contribution of tree species to the biodiversity of a 1ha Old World rainforest in Brunei, Borneo

Tree biodiversity data is presented for a 1-ha permanent study plot on a low slope position of the Kuala Belalong valley in Temburong District, Brunei, Borneo. This is the first study in the region to document the tree flora of a low slope. All trees 5cm at 1.3m were mapped, measurements of dbh and height taken, and identified to species and morpho-species level. The total and relative values of each family for density, diversity, dominance and Importance Value Indices were calculated. A total of 1062 stems were recorded on the plot (1019 live, 43 dead) with a total of 278 species representing 110 genera in 49 families. The most ecologically significant family as determined by the Family Importance Value (FIV) was Euphorbiaceae with a value of 40 and'the'most significant species, using the Importance Value (IV), was morpho-speciesFordia splendissima with an IV of 29. The total basal area of all living trees was 31.43m². Forest structure was marked by a few tall (>45m) emergents, for example,Koompassia excelsa, Crypteronia griffithii and two species of the Dipterocarpaceae family, however, lower understorey and sub-canopy species dominated the plot with the average height of all individuals over the hectare being 11m.