Spatial pattern of diversity in a tropical rain forest in Malaysia

The diversity of trees (species richness, abundance and Shannon diversity) in a tropical rain forest of Malaysia has been studied from the point of view of its spatial organization in order to formulate hypotheses about the origin of the observed spatial patterns. The question that motivated this study is whether tropical forests communities are in a state of equilibrium or non-equilibrium. Three aspects have been examined: (1) changes in diversity were studied with respect to sampling area and sampling designs. A minimum area of 5-10 ha is recommended by the species-area curves, while 2-5 ha seem appropriate based on the Shannon diversity-area curves. Different sampling designs significantly affect the species area curves. The power function, which can be derived under the equilibrium assumption, is not appropriate to fit the observed diversity-area curves. (2) The spatial features of diversity variables were then studied. Variograms showed that there are dominant short-range effects (around 150m), obvious anisotropic distribution, and high random variation in the diversity data. (3) Partitioning the variation of the diversity measures into environmental (topographic) and spatial components indicated that the spatial organisation of that community was mostly unpredictable. There may be many processes controlling the formation of the spatial patterns in the tropical rain forest. Unidentified causes, affecting mainly the small-scale processes (<20 m), seem responsible for the large amount of undetermined variation in the diversity data sets. The study suggests that the Pasoh forest of Malaysia may not be in a state of equilibrium.