Location and General Description
This ecoregion represents the peat swamp forests along the eastern coast of the island of Sumatra, Indonesia. Based on the Köppen climate zone system, this ecoregion falls in the tropical wet climate zone (National Geographic Society 1999).
The peat swamp forests of Sumatra have similar characteristics to those in Borneo and peninsular Malaysia. Peat soil is composed of more than 65 percent organic matter (Driessen 1978). Most peat deposits found behind mangroves along the coast are ombrogenous, or rain-fed peat swamps (Driessen 1977; Morley 1981). Peat swamp forests are formed when rivers drain into the inland edge of a mangrove and the sediments are trapped behind the tangle of mangrove roots. These areas begin to build up and flood less often as the coastline extends outward. The peat deposits usually are at least 50 cm thick but can extend up to 20 m. Peat swamps are domed and are rarely flooded. Because peat swamps are not drained by flooding, they are nutrient deficient and acidic, with a pH usually less than 4. Compared with other moist forest ecoregions, peat forests-at least in the lowlands-are not as species-rich and are not high in endemism (WWF and IUCN 1991).
There is not a single type of peat swamp forest but rather a gradation of forests types along a nutrient gradient. The edges of peat swamp forests are relatively nutrient-rich, whereas the center is nutrient-poor (Whitten et al. 2000). Likewise, the forest becomes smaller with an even canopy, moving from the edges to the center. Whereas Borneo has up to six types of peat swamp forest, Sumatra retains only two: a mixed peat swamp forest and a pole forest.
Both mixed swamp forest and pole forest have few tree species, but a pole forest may have a higher density. Mixed swamp forests tend to have a larger average diameter and basal area. Some characteristic species from these forests include Tristania obovata, Ploiarium alternifolium, Polyalthia glauca, Stemonurus secundiflorus, Radermachera gigantea, Salacca conferta, Livistona hasseltii, and Cyrtostachys lakka (Whitten et al. 2000). Palms are not common, but several species generally are confined to these forests. The emergent Livistona hasseltii is characteristic, as is the bright-red sealing wax palm Cyrtostachys lakka.
Peat swamp forests do not support an abundance of terrestrial wildlife, and none of the mammals are considered endemic. The Sumatran tiger (Panthera tigris) is Indonesia's largest terrestrial predator and is critically endangered (IUCN 2000). The Sumatran tiger lives in lowland and montane rain forest and frequent peat swamp forests throughout Sumatra. An estimated 500 Sumatran tigers remain in Sumatra (Franklin et al. 1999). There are three Level II TCUs in Sumatra that overlap this ecoregion (Dinerstein et al. 1997). The Asian elephant (Elephas maximus) is found in numerous populations throughout Sumatra. However, only five populations have more than 200 individuals, but habitat loss has placed the survival of many of these populations at risk (Sukumar 1989). The number of bird species tends to be lower in peat swamp forest than in the surrounding lowland rain forests, and there are no endemic or near-endemic species.
More than half of the habitat in this ecoregion has been cleared, especially in the southern portion, where only a few blocks of habitat remain. Large areas of swamp have been drained, mainly for transmigration settlements and large-scale development projects, making this a highly vulnerable ecoregion. There are thirteen protected areas that extend into the ecoregion to cover 4,730 km2 (5 percent) of the area (table 2). However, many of the protected areas are proposed, and the official status is still uncertain. Of the gazetted protected areas, only Berbak is greater than 1,000 km2.
Table 1. WCMC (1997) Protected Areas That Overlap with the Ecoregion.
Protected Area Area (km2) IUCN Category
Bakau Selat Dumai [AA0124] 320 PRO
Bukit Batu 230 PRO
Siak Kecil 940 PRO
Danau Tanjung Padang 110 PRO
Giam Duri [IM0157] 200 PRO
Pulau Burung [AA0124] 260 I
Berbak [AA0124] 1,310 II
Istana Sultan Siak 240 PRO
Danau Belat/Besar Serkap 80 PRO
Sarang Barung 40 PRO
Kerumutan 110 IV
Kerumutan Lama 40 PRO
Padang Sugihan 850 IV
Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.
Types and Severity of Threats
In some areas of southern Sumatra, the peat swamp has been drained for transmigration and other major development projects. The drainage of one area dries neighboring areas. Therefore, fires are common, preventing natural succession and promoting the development of extensive, nearly monospecific stands of paperbark (Melaleuca cajuputih) (Whitten et al. 2000). In areas where the peat itself is burned, small, shallow lakes form and become covered with floating islands of grasses and herbs (Whitten et al. 2000). Large-scale plantations, illegal logging, and timber enterprises have also led to increasing deforestation with resultant erosion and sedimentation of nearby rivers (WWF-Indonesia n.d.). Coconuts are grown along the coast, and drained swamps are used for pineapple plantations (MacKinnon and MacKinnon 1986). Logging concessions cover almost 80 percent of the ecoregion's remaining habitat and pose a serious threat to habitat integrity and conservation.
Justification of Ecoregion Delineation
Whitmore (1984a) and MacKinnon (1997) showed large extents of peat swamp forests along the northern coast of Sumatra, especially in Riau Province. We delineated the Sumatran Peat Swamp Forests [IM0160] to represent these forests but extracted the smaller patches of freshwater swamp forests into the Sumatran Freshwater Swamp Forests [IM0157] and the mangroves in the Sunda Shelf Mangroves [IM1405].
MacKinnon's biounit 21 largely corresponds to Udvardy's Sumatra biogeographic province. However, Udvardy did not include the Nicobar Islands. Eight ecoregions overlap Udvardy's Sumatra biogeographic province: Sumatran Lowland Rain Forests [IM0158], Sumatran Montane Rain Forests [IM0159], Mentawai Islands Rain Forests [IM0127], Sumatran Peat Swamp Forests [IM0160], Sumatran Freshwater Swamp Forests [IM0157], Sundaland Heath Forests [IM0161], Sumatran Tropical Pine Forests [IM0304], and Sunda Shelf Mangroves [IM1405].
References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List
Prepared by: Colby Loucks and Tony Whitten