Primary lowland dipterocarp forest at Danum Valley, Sabah, Malaysia: structure, relative abundance and family composition

Abstract Trees greater than or equal to 10 cm gbh were enumerated, mapped and identified in two 4 hectare (ha) (40 000 m2) plots in 1985-1987. The number of species recorded was 511 (in 164 genera and 59 families) in a total sample of 17 985 individuals. Plots 1 and 2 contain 388 and 387 species respectively, and for trees greater than or equal to 30 cm gbh there are 247 and 242 species. Relative abundance patterns were fitted to a logseries distribution. In each plot, 51% of species are rare (f < 5) and 31% have only one tree ( f = 1). Common species ( f ≥ 5 ) achieve a minimum area at 2 ha. The plots are close ‘replicates’ in many respects, and 8 ha gives an adequate sample. The mean density of trees greater than or equal to 10 cm gbh and 30 cm gbh is 2248 ha-1 and 470 ha-1, with corresponding basal areas of 30.7 m2 ha-1 and 26.6 m2 ha-1 . The linear relation between In frequency and In gbh, the small (0.5% ) ground area of gaps, and the low contribution by pioneer species show little recent disturbance. Dominance by 2-4 understorey species is pronounced. For trees greater than or equal to 30 cm gbh, the Euphorbiaceae contribute the most to density at 21% , with Dipterocarpaeceae second at 16%: corresponding basal areas are 7% and 49% . For trees greater than or equal to 10 cm gbh, density of the Euphorbiaceae reaches 28% , Dipterocarpaceae 9% , followed by Annonaceae 8% , Lauraceae 7% and Meliaceae 6% . Lauraceae was the most species-rich family (83 species), then Euphorbiaceae (51 species) and Meliaceae (36 species). Compared with the means of nine other sites in this forest type, Danum has 84% of the density and 74% of the basal area for trees greater than or equal to 30 cm gbh; and 60% of the species richness for this size class on a 1-1.6 ha basis. The forest is differentiated by its dominance by Euphorbiaceae, in terms of tree density, and the high contributions made by Lauraceae and Meliaceae. These attributes may reflect special site conditions and/or a late stage in recovery from past disturbance.