The Sundaland heath forests, also known as Kerangas forest, is a type of tropical moist forest found on the island of Borneo, which is divided between Brunei, Indonesia, and Malaysia, as well as on the Indonesian islands of Belitung and Bangka, which lie to the west of Borneo.
Setting
The word Kerangas, which means "land which cannot grow rice", comes from the Iban language. Heath forests occur on acidic sandy soils that are the result of the area's siliceous parent rocks. Permanently waterlogged heath forests are known as kerapah forests.[2] Open-canopied woodlands are known as padang.[3] 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.[2]
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. Moreover, heath forests' low soil pH hampers organic matter decomposition thus further slowing nutrient cycling.[4][5]
Flora
The Sundaland heath forests are distinct from the surrounding Borneo lowland rain forests in species composition, structure, texture, and color. The heath forests typically have a low, uniform canopy approximately 20 metres high, with thick underbrush and rich growth of moss and epiphytes. Trees often have closely-spaced trunks.[2] In contrast, padang woodland is relatively open, with shrubs and trees up 5 metres tall, and a ground layer of sparse grasses and sedges.[3]
Leaf sizes are generally smaller than other lowland rain forest trees. As an adaptation to the nutrient-poor conditions, some heath forest species have small, hard, thick sclerophyll leaves which are low in nitrogen.[3] Many tree and plant species in the nutrient-deprived heath forests have developed unconventional ways to get their nutrients. Some tree species (Gymnostoma nobile, for example) utilise rhizobia (nitrogen fixingbacteria) in their root nodules. Myrmecophytes, including Myrmecodia spp. and Hydnophytum spp., are tree species that develop symbiotic associations with ants to get their nutrients. Other plants, including pitcher plants(Nepenthes spp.), sundews(Drosera spp.), and bladderwort(Utricularia spp.), are carnivorous, trapping and digesting insects.[2]
^Eric Dinerstein, David Olson, et al. (2017). An Ecoregion-Based Approach to Protecting Half the Terrestrial Realm, BioScience, Volume 67, Issue 6, June 2017, Pages 534–545; Supplemental material 2 table S1b. [1]Archived 2020-10-09 at the Wayback Machine
^ abcdefWikramanayake, Eric; Eric Dinerstein; Colby J. Loucks; et al. (2002). Terrestrial Ecoregions of the Indo-Pacific: a Conservation Assessment. Island Press; Washington, DC.
^ abcHazimah Din, Faizah Metali, Rahayu Sukmaria Sukri, "Tree Diversity and Community Composition of the Tutong White Sands, Brunei Darussalam: A Rare Tropical Heath Forest Ecosystem", International Journal of Ecology, vol. 2015, Article ID 807876, 10 pages, 2015. https://doi.org/10.1155/2015/807876
