Structural and floristic variation among small replicate plots of a tropical montane forest on Mount Kinabalu, Sabah, Malaysia

Abstract

We examined the variation in forest structure, species diversity and floristic composition of trees for different minimum sizes (≥ 4.8 cm and ≥ 10 cm stem diameter) in six 0.25-ha plots of a tropical montane forest (1600 m above sea level) on Mount Kinabalu, Sabah, Malaysia. Four plots are parts of a 2.74-ha plot, and two are located 75 m and 200 m apart from the others. In all, the six plots are distributed in an area of approximately 8 ha (450 m × 175 m) on similar topography (sideslopes). Forest structure (e.g. stem density, basal area and estimated aboveground biomass) appeared to be similar among the six plots. Tree species richness per plot varied little (91-102 for stems ≥ 4.8 cm diameter and 60-72 for stems ≥ 10 cm diameter). Several indices of species diversity (or evenness) were also within narrow ranges, correlated with species richness. The dominance of species varied greatly among the six plots, but that of genus and family was relatively consistent. Analysis based on the 2.74-ha plot suggested that this reflected different habitat associations with microtopography among congeneric or confamilial species and intraspecific aggregation. Similarity indices based on presence/absence of species (e.g. Jaccard and S.rensen indices) were negatively correlated with spatial distances between plots (for stems ≥ 4.8 cm diameter), but those based on relative abundance of species were not. Indices of species diversity (or evenness) and similarity based on basal area were correlated between two minimum sizes (≥ 4.8 cm and ≥ 10 cm diameter), but those based on number of stem or presence/absence of species were not. We concluded that variations in forest structure, tree species diversity and floristic composition at genus and family levels were small at this spatial scale, and that the results obtained in any single 0.25-ha plot can be reasonably extrapolated to the other stands on similar topography in this area except dominance of species.