The Ecology of Podocarps in Tropical Montane Forests of Borneo: Distribution, Population Dynamics, and Soil Nutrient Acquisition

Abstract

We review the ecology of podocarps on various soil types in Borneo, largely relying on our studies conducted on Mount Kinabalu. Podocarps are generally abundant in montane forests, but their abundance varies with soil nutrient status, and they can occur in lowland forests where soil nutrients are scarce. These patterns suggest control by soil nutrients rather than by temperature. Analyses of population structure, growth rate, and crown light conditions in montane forests indicate that podocarps are generally shade intolerant and require canopy gaps or sparse canopy for regeneration. Podocarps have greater maximum tree sizes than most co-occurring angiosperm species in Mount Kinabalu forests. Once they reach the upper canopy layer, they persist for a long time because of their long life span, allowing them to regenerate in rare events of canopy disturbance. The roots of two podocarp species (Dacrycarpus imbricatus and Dacrydium gracile) showed a greater acid phosphatase activity when compared with angiosperm roots within the same lower montane forest. Moreover, an analysis using lipid biomarkers indicated that saprophytic fungi are more abundant in the soils beneath the two podocarps than beneath angiosperms, and a fungal biomarker lipid correlated with soil acid phosphatase activity. The dominance of saprophytic fungi appears to be related to high soil acid phosphatase activity, suggesting feedback effects between the podocarps and soil microbial communities. These results indicate that podocarps are efficient in the acquisition of phosphorus from the acidic montane soils and decomposing litter. We suggest that the architectural and life history advantages and physiological adaptations to nutrient limitation are essential for the persistence of podocarps, despite their lower shade tolerance as compared to angiosperms.