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Sundaland heath forests
Sundaland heath forests
	Padang scrub at Bako National Park
	Ecoregion territory (in purple)
Ecology
Realm	Indomalayan
Biome	tropical and subtropical moist broadleaf forests
Borders	List Borneo lowland rain forests; Borneo montane rain forests; Borneo peat swamp forests,; Southwest Borneo freshwater swamp forests; Sumatran lowland rain forests;
Geography
Area	76,130 km2 (29,390 sq mi)
Countries	Indonesia; Malaysia;
Conservation
Conservation status	critical/endangered
Protected	6,436 km2 (8%)

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 fixing bacteria) 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]

Dipterocarps, including species of Shorea and Hopea, are common canopy trees on less barren soils, along with palms. Native trees include both heath forest endemics, typical lowland forest species, and species shared with peat swamp forests like Shorea albida, Shorea pachyphylla, and Shorea scabrida. Heath forests are also characterized by many plants of Australasian origin, including trees of families Myrtaceae and Casuarinaceae and the southern hemisphere conifers Agathis, Podocarpus, and Dacrydium.^[2]

Fauna

The heath forests generally have less wildlife and species diversity than the surrounding lowland rain forests, with little or no endemic species.^[2]

Protected areas

9.695% of the ecoregion is in protected areas. These include:^[6]

References

^ 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]
^ ^a ^b ^c ^d ^e ^f Wikramanayake, Eric; Eric Dinerstein; Colby J. Loucks; et al. (2002). Terrestrial Ecoregions of the Indo-Pacific: a Conservation Assessment. Island Press; Washington, DC.
^ ^a ^b ^c Hazimah 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
^ Sellan, Giacomo; Thompson, Jill; Majalap, Noreen; Robert, Rolando; Brearley, Francis Q. (2020-05-01). "Impact of soil nitrogen availability and pH on tropical heath forest organic matter decomposition and decomposer activity" (PDF). Pedobiologia. 80: 150645. Bibcode:2020Pedob..8050645S. doi:10.1016/j.pedobi.2020.150645. ISSN 0031-4056. S2CID 218789907.
^ Proctor, J. (1999) "Heath forests and acid soils". Botanical Journal of Scotland 51, 1-14.
^ Sundaland heath forests. DOPA Explorer. Accessed 1 April 2023.