Soil environment and tree species diversity in tropical rain forest, West Sumatra, Indonesia

Abstract

Soil characteristics were examined in relation to tree species diversity of a tropical rain forest on a 100 m transect plot covering from ridge to valley with 0.10 ha and a long-term observation plot, 1.0 ha, in Mt. Gadut area near Padang, West Sumatra, Indonesia. The area experienced an annual rainfall of more than 6000 mm with no real dry season. In the 0.10 ha transect plot, detailed soil characterization was performed. From each sub-plot having the measurements of 5 × 5 m, 5 samples were taken from each 0–5 and 5–15 cm depth. In this transect plot, the subplots positioned on the ridge showed a greater diversity of tree species and higher biomas than those positioned in the valley. Soils found on the ridge showed less fertility and greater variation of fertility characteristics than those found in the valley. The examination of vertical soil profile distribution of ridge, middle and valley positions in this transect also revealed that exchangeable Calcium, total carbon and total nitrogen of ridge soil tended to accumulate of these nutrients at the upper horizons and of dissipation at lower horizons more than those of valley soil profile. Detailed characterization of 115 subplots of 1.0 ha permanent plot showed that horizontal variations of soil fertility characteristics were also important in relating the tree species diversity of tropical rain forest. These results suggest that both vertical and horizontal variations of soil characteristics are imperative in supporting the tree species diversity.