Kerangas forest

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Tropical heath forest, also known as kerangas forest, is a type of forest found on the island of Borneo, especially in Brunei, as well as on the islands of Belitung and Bangka, which lie to the west of Borneo. They are often of smaller stature than more typical lowland evergreen rain forests and have a more even canopy layer, smaller leaves and reduced species diversity.

The word Kerangas, which means "land which cannot grow rice", came from the Iban language. Heath forest occurs on acidic sandy soils that are the result of the area's siliceous parent rocks. The sandy soil of the heath forest are often lacking in nutrients; it is generally considered that nitrogen is the nutrient which is most lacking for plant growth in these forests. This is in contrast to many other lowland rain forests where phosphorus is considered to be lacking. Therefore, most of the trees and plants species develop another way to get their nutrients. Some tree species utilised rhizobia (nitrogen fixing bacteria) in their root nodules, for example, Gymnostoma nobile and Myrmecophytes tree species develop symbiotic associations with ants to get their nutrients. Other plant species become carnivorous through digesting insects, example pitcher plants (Nepenthes spp.)

A more recent hypothesis, proposed by Proctor (1999), is that these forests are growing on soils which are highly acidic, such that hydrogen ion toxicity prevents the growth of non-adapted species.

Proctor, J. (1999) Heath forests and acid soils. Botanical Journal of Scotland 51, 1-14.