Although the Borneo peat swamp forests are not as biodiverse as neighbouring lowland rainforests, the Borneo Peat Swamp Forests are some of the most speciose peat swamp forests in Southeast Asia. Peat swamp forests are a key habitat for the unique endangered Borneo endemic proboscis monkey (Nasalis larvatus). They are also home to the world's most desirable aquarium fish, the arowana (Scleropages formosus).
Location and general description
This ecoregion is made up of the peat swamp forests along the western coasts of the island of Borneo, within the Malaysian state of Sarawak and Indonesian Kalimantan. Most of the peat swamp forests are associated with coastal areas, but two large areas of peat swamp forests occur around Lake Mahakam and Lake Kapuas. Based on the Köppen climate zone system, this ecoregion falls in the tropical wet climate zone.
The peat swamp forests of Borneo have vegetative and edaphic characteristics similar to those in Sumatra and peninsular Malaysia. The peat soil is predominantly organic matter, which builds up behind mangrove swamps. These soils are ombrogenous, or rain-fed, and are recent in origin. Peat swamp forests form when sediments build up behind mangroves as rivers drain toward the coast. These areas build up with organic matter over time and eventually form domes that are rarely flooded. These peat deposits can extend down to 20 meters. Because peat swamps are not drained by flooding, they are nutrient-deficient and acidic (pH usually is less than 4). Compared with other moist forest ecoregions, peat swamp forests are not as species-rich or high in endemics.
Peat swamp forests encompass a sequence of forest types distributed from the perimeter to the center of each swamp. Six forest communities that have a distinct structure, physiognomy, and flora are discernible. The first type is similar to, yet less rich than, lowland dipterocarp evergreen rain forests that occur on mineral soils. These forests are dominated by Gonystylus bancanus (the single most valuable timber species), Dactylocladus stenostachys, Copaifera palustris, and four Shorea species. Shorea albida plays a major role in the swamp forest communities and dominates forest types two through four. Forest type four is also characterized by Calophyllum obliquinervum, Cratoxylum glaucum, and Combretocarpus rotundatus. The principal species in forest type five are Tristania obovata, Palaquium cochleariifolium, and Parastemon spicatum, and type six resembles open savanna woodland, with the most abundant species being Dactylocladus stenostachys, Garcinia cuneifolia, Litsea crassifolia, and Parastemon spicatum. Other genera of trees often found in Sarawak's peat swamp forests include Dryobalanops and Melanorrhea.
Most of the tree families of lowland dipterocarp forests are also found in peat swamp forests. Exceptions include Proteaceae, Lythraceae, Combretaceae, and Styraceae. Few plant species are endemic to peat swamp forests, mainly because of their recent formation. Many species found in the most acidic central portion of peat swamp forests also occur in heath forests. Brünig found 146 species common to both forest types. More than thirty palm species are found in peat swamp forest, including the red-stemmed sealing wax palm, Cyrtostachys lakka.
Many animal species occur in peat swamp forests, but only the Borneo roundleaf bat, Hipposideros doriae, and two birds, the Javan white-eye (Zosterops flavus) and the hooked-billed bulbul (Setornis criniger), are considered near endemic (Table 1, Table 2). With only two exceptions, monkeys, gibbons, and orangutans are all found in Borneo's peat swamp forests, but at lower densities. Long-tailed macaques (Macaca fascicularis) and silvered langurs (Presbytis cristata) have higher densities in peat swamp forests than in lowland rain forests, but only along [[river]s. Forest productivity is higher at the river's edge, with additional nutrient and light inputs.
|Table 1. Endemic and Near-Endemic Bird Species.|
|Pycnonotidae||Hook-billed bulbul||Setornis criniger|
|Zosteropidae||Javan white-eye||Zosterops flavus|
Peat swamp forests are key habitats for the unique proboscis monkey (Nasalis larvatus). These monkeys are found only in coastal and riverine habitats in Borneo. They are good swimmers and will swim across rivers, despite the presence of crocodilian predators. Proboscis monkeys are often found along the rivers in the afternoon, where they sleep in tall lookout trees. They eat primarily young leaves and the seeds of unripe fruit. Like other colobines, they have developed highly complex sacculated stomachs with specialized bacteria to digest this diet.
|Table 2. Endemic and Near-Endemic Mammal Species.|
|Rhinolophidae||Borneo Roundleaf Bat||Hipposideros doriae|
Bird species diversity tends to be lower in peat swamp forests than in the surrounding lowland rain forests. However, in Tanjung Puting National Park, a freshwater and peat swamp reserve in Kalimantan, more than 200 bird species were recorded.
One of the most desirable and rare aquarium fish, the arowana (Scleropages formosus), is found in deep pools in peat swamp rivers. These rivers also support other typical riverine fauna such as otters, waterbirds, false gavials, crocodiles, and monitor lizards.
Peat swamp forests used to be extensive in Sarawak and also occurred in southwestern Sabah. However, today about half of the area has been cleared. Brunei's peat swamp forests are probably less disturbed than examples elsewhere in the region. Some of those on the Belait River are still in a pristine condition: they may soon represent the only undisturbed forests of this type in the region. The eleven protected areas cover 4,300 km2 (6 percent) of the ecoregion. Tanjung Puting, Muara Sebuku, and Kelompok Hutan Kahayan each protect more than 500 km2 of contiguous forest (Table 3). The peat swamp forests are represented in Brunei's protected area network.
|Table 3. Protected Areas That Overlap with the Ecoregion.|
|Protected Area||Area (km2)||IUCN Category|
|Kelompok Hutan Kahayan||680||PRO|
|Danau Semayang Sungay Mahakam||330||PRO|
|Muara Kaman Sedulang||290||I|
In 1997-1998, fires originally set intentionally to clear forests for commercial agriculture and forestry companies were intensified by the region's drought, destroying vast tracts of Borneo's lowland forests. More than 7,500 km2 of peat swamp forest were burned in this two-year period. Kutai and Muara Kaman suffered extensive, severe damage during the fires, with almost no area left untouched. Peat swamp forests are particularly vulnerable to fire. During burning, they produce the most carcinogenic haze of any forest type through the release of large amounts of fine particulate matter. The haze so produced during 1997-1998 covered most of Indonesia and Malaysia and extended north to Thailand and Bangkok. Peat fires typically burn underground as well as above, not only eliminating the seedbank but also destroying the soil: this may take thousands of years to replenish.
The fires also had adverse effects on the wildlife. Unknown numbers of birds, reptiles, amphibians, primates, and mammals died in the fires or shortly after due to the scarcity of food. Hundreds of orangutan were killed by villagers for meat, and their orphaned babies were sold to the international pet trade as they fled into villages to escape the fires. Fires are a major threat to the continued existence of the endangered orangutan. The charismatic proboscis monkey was the primate species that lost the greatest percentage of habitat to the fires because large areas of riverine and coastal habitats were also destroyed.
Types and severity of threats
Peat swamp forests were the first formations to be logged on a commercial scale in Sarawak and for many years were the main source of timber. In Brunei, peat swamp forests are still intact, but are threatened by the planned expansion of forestry operations, which may result in overexploitation of forests rich in Shorea albida. The continual threat of fires clearing forest for oil palm and other commercial agriculture crops will loom over Indonesia until stricter forest policies and protection are taken.
Justification of ecoregion delineation
The large island of Borneo was divided into nine ecoregions. Most of the island's lowland and submontane forests are dominated by dipterocarp species. MacKinnon and MacKinnon divided the island's lowland forests into six subunits, in addition to a central subunit representing the montane forests. These authors revised the boundaries of these seven subunits but retained the same general configuration. MAcKinnon and MacKinnon used the major rivers, the Kapuas and Barito, to represent zoogeographic barriers to a few species of mammals and based subunits largely on these barriers, but also used climatic regimes for the drier eastern biounits.
- Li and Sun. 1999. Palynological records since Last Glacial Maximum from a deep-sea core in the southern South China Sea. Quat. Sci. Rev. 23: 2007-2016
- Pinxian Wang. 2009. The South China Sea: Paleoceanography and Sedimentology (Google eBook) Springer. 506 pages
- Eric D.Wikramanayake. 2002. Terrestrial ecoregions of the Indo-Pacific: a conservation assessment. Island Press. 643 pages
Additional information on this ecoregion
- For a more terse summary of this entry, see the WWF WildWorld profile of this ecoregion.
- Forests of Borneo
- Malaysia Geography Collection
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