Structure, floristics and diversity of tropical montane rain forests over ultramafic soils on Mount Kinabalu (Borneo) compared with those on non-ultramafic soils

We describe here the structure, floristics and diversity of tropical montane rain forests over ultramafic soils on Mount Kinabalu, Borneo, and compared them with those on non-ultramafic soils. We used 14 sample plots from 1580 to 3080m elevation, six on ultramafic soils and eight on non-ultramafic soils, and identified all trees 4.8cm diameter. The plot area ranged from 0.1 to 1ha, the majority (nine plots) being 0.25ha. Forests on ultramafic soils showed more stunted structure, especially at higher altitudes, than those on non-ultramafic soils and on ridges than on slopes. Species of Coniferae (Araucariaceae and Podocarpaceae) and Myrtaceae strongly dominated on ultramafic soils occupying 61-96% of basal area in each plot, compared with 22-63% on non-ultramafic soils. Among 287 species found in the 14 plots, only nine species (including four species endemic to Mount Kinabalu) were strictly restricted to ultramafic soils. Nonmetric multidimensional scaling demonstrated that elevational change in species composition was accelerated on ultramafic soils and on ridges. Tree species diversity was generally lower on ultramafic soils than on non-ultramafic soils at the comparative altitudes. Multiple regression analysis suggested that soil nutrients (phosphorus and nitrogen) could be the cause of vegetation differentiation between ultramafic and non-ultramafic soils, although the data on soil metals are lacking. Comparison of our results with those from other mountains with ultramafic soils in South-east Asia demonstrated the uniqueness of the montane rain forests over ultramafic soils on Mount Kinabalu.