Tropical Rain Forest Biodiversity Analyzed by a Large Research Plot

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The species richness of a tropical rain forest was analyzed by using a large-scale research plot, which has a size of 52 ha and was established at the Lambir National Park, Sarawak, Malaysia in 1993. Questionnaires of the present study are mainly concerned with the tests of availability of two contrasting hypotheses, equilibrium hyporthesis (niche theory) and non-equilibrium hypothesis, for the explanations of working mechanisms of the biodiversity of tropical rain forest. By dividing the whole plot area into 1300,20mx20m stands, four topographic and five forest-structural variables were calculated for each of 1300 stands. The topographic variables suggested the steeply sloped, sharply undulating, and complexly bisected topography of the plot. The forest structural variables also suggested a huge and complex structure with superimposed forest layrs. Both topographic and structural variables were highly correlative, suggesting a predictability of forest structure with respect to topography. Out of the five forest structural variables, mean dbh per forest layr in a 20mx20m stand decreased with and increase of tree density per forest layr, showing a density dependency of individual tree growth. The total number of species in the plot was 1175, which was far greater than those at Pasoh (820 spp/50ha) in west Malaysia and BCI (306) spp/50ha) in Panama. The spatial patterns of some dominant species were also highly correlative with topographic variables. All these results suggested the predictable change of the huge and complex architecture of the rain forest at Lambir and seemed to be favored by the equilibrium hypothesis as a working mechanism of tropical biodiversity. The genetic diversity was studied by analyzing isozyme patterns in leaves and implied the importance of gene drifts for producing the rich tropical biodiversity.