Included here is Borneo (Kalimantan) and adjacent islands such the Bunguran (Natuna) Islands, Calamian Islands, Jolo Island, Laut Island, Palawan Island, Pangutaran Islands and the Tawitawi Islands.

Bornean Limestone Forest

In the lowlands these forests are often dominated by large emergent tree reaching heights of 40 m or so. Dipterocarps, such as the endemic Hopea andersonii, H. dasyrachis and Shorea patoiensis (Dipterocarpaceae) are common together with nondipterocarps like Brownlowia glabrata and Palaquium sericeum. Many of these large trees are heavily buttressed. Other trees include various endemics such as Aglaia ramotricha (Meliaceae), Chisocheton ruber (Meliaceae), Daphniphyllum dichotomum (Daphniphyllaceae), Osmoxylon kostermansii (Araliaceae), Tristiropsis ferruginea (Sapindaceae) together with the two endemic palms Livistona exigua and Pinanya yassinii (Arecaceae). The shrub layer is sparse but several epiphytic shrubs may be present like the endemic Vaccinium lobbii (Ericaceae). Large woody climbers are also less common than in the dipterocarp forests but may, for example, include species of Derris and Phanera.  Surprisingly, the epiphytic flora is also comparatively poor especially in the more shady areas, but may include the endemic fern Pyrrosia platiphylla (Polypodiaceae). Moving into the montane zones, dipterocarps decrease in number although Hopea argentea often persists well into the uplands. More typical here are species such as Casuarina nobilis while in the upper zones above 1200 m the conifers Dacrydium beccarii and Phyllocladus hypophyllus come to dominate. Knema sericea (Myristicaeae) is one of many endemic trees, and there are many shrubby species including a number of endemic rhododendrons, and several endemic ferns such as Ctenitis muluensis (Tectariaceae). In fact, these limestone forests have extremely high levels of endemism.

Bornean Ultrabasic Forest

Ultrabasic rocks only account for about 1% of the land area of Borneo being mostly confined to Sabah and South Kalimantan. It is rich in nickel and chromium, which is toxic to many plants and so often supports an assemblage of specially adapted species. However, unlike New Caledonia where the forest on ultrabasic rock is very distinctive, here there is less demarcation between the ‘untrabasic’ forests and those of the surrounding areas. Nevertheless, several dipterocarps including the endemic Dipterocarpus geniculatus, Shorea andulensis and S. laxa together with a few other endemic trees such as Borneodendron anaegmaticum (Euphorbiaceae) and Buchaninia arborescens (Anacardiaceae) are more or less confined to ultrabasic soils. In the uplands shrubs such as Leptospermum recurvum and the endemic Dacrydium gibbsiae (Podocarpaceae) become the main species, while other shrubs may include the endemic Rhododendron ericoides (Ericaceae). Here the ground layer can be almost barren in places with just a few tufts of Machaerina micrantha, Schoenus curvulus and the endemic Euphrasia borneensis (Scrophulariaceae). However, endemism in general on ultrabasics is far less pronounced in Borneo than it is compared with, for example, New Caledonia, where some 79% of the species on these soils are found no where else. The few species endemic to Borneo that seem to be mainly found on ultrabasics including several trees like Atuna cordata (Chrysobalanaceae), Dipterocarpus ochraceus (Diperocarpaceae), Podocarpus confertus (Podocarpaceae) and Quercus kinabaluensis (Fagaceae).

References

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