The stand structure of a mixed dipterocarp forest was analyzed by using the data obtained from a fifty-two hectare research plot at the Lambir National Park, Miri, Sarawak, East Malaysia. The range of data analyses in the present study was confined to the topics of physiognomy while awaiting species identification data. The forest height evaluated by a height curve model of a hyperbolic equation was the tallest in Lambir among three research sites, Barro Colorado Island in Panama, Pasoh in West Malaysia, and Lambir in East Malaysia. By dividing the 52 ha plot into 1300 stands of 20 m &time; 20 m, the physiognomic dimensions, such as the biomass, tree density, maximum dbh, and basal area per stand, were calculated and their dependency on topography was statistically tested. The results of statistical tests suggest that the significant differences of physiognomic dimensions between stands are marked by different topographic conditions in terms of slope altitudes, angles, directions, and convexity degrees. The correlated change in physiognomic dimensions and local topography implies the dependency of the relative occurrence of three growth phases (gap, building, and mature phases) in the forest growth cycle upon topography. The size structure of the stands was analyzed by using dbh data and by assuming the exponential distribution of dbh. The stands were characterized by stratified subpopulations, whose total number per stand was in a range between two and seven. The variation in the number of sub-populations per stand corresponded well to the altitude difference between stands, suggesting correlated gradients in the forest stratification, forest growth cycle, and topography. All these results suggest the presence of predictable change of the huge and complex architecture of the rain forest at Lambir in relation to topography or environmental conditions such as soil and water. In these respects, the results seem to be favored by an equilibrium hypothesis rather than non-equilibrium hypothesis as a working mechanism of tropical biodiversity, though floristic composition can be independent from physiognomic dimensions.
1996 The Japan Society of Tropical Ecology