Location and General Description
This ecoregion represents the disjunct patches of freshwater swamp forests along the eastern alluvial plain on the Indonesian island of Sumatra. Based on the Köppen climate zone system, this ecoregion falls in the tropical wet climate zone (National Geographic Society 1999).
The major difference between freshwater swamp forests and peat swamp forests is the lack of deep peat, and the source of water is riverine and rainwater. Freshwater swamp forests grow on fertile alluvial soils, and the wide variety of soils is reflected in a diversity of vegetation types that ranges from grassy marshes to palm or Pandanus-dominated forest and forests similar in structure and composition to lowland rain forests. Trees with buttresses, stilt roots, and pneumatophores are common in some areas (Whitten et al. 1987). Trees in freshwater swamp forests endure prolonged periods of flooding, causing the soils to become anaerobic. Pneumatophores, specialized respiratory structures on the roots, are common on many tree species and assist in respiration during oxygen-poor periods. Emergent trees attain heights of 50-60 m (FAO 1981). These forests are floristically very variable; the dominant species include Adina, Alstonia, Campnosperma, Coccoceras, Dillenia, Dyera, Erythrina, Eugenia, Ficus, Gluta, Lophopetalum, Memecylon, Metroxylon, Pandanus, Pentaspadon, Shorea, and Vatica spp. (FAO 1981). Melaleuca leucadendron covers extensive areas in the south of this ecoregion (FAO 1981).
The freshwater swamp forest fauna is much more diverse than the fauna of peat swamp forests, being more similar to that of lowland rain forests. Many of the characteristic species of lowland rain forests are also found here, although these forests contain no endemic mammal or bird species. However, they are home to Asia's largest terrestrial mammal, the Asian elephant (Elephas maximus), which is found in numerous populations throughout Sumatra. However, only five populations number more than 200 individuals, and with the rapid habitat loss the survival of many of these populations is uncertain. Way Kambas, a freshwater swamp forest reserve in southern Sumatra, contains one of these populations (Sukumar 1989). The endangered Malayan tapir (Tapirus indicus), the largest of the four living tapir species and only Old World representative, is also a resident of these forests. The Sumatran population of the Malayan tapir is close to extinction, with no more than fifty animals left in the wild (McClung 1997). Another endangered species, the Sumatran tiger (Panthera tigris), Indonesia's largest terrestrial predator, lives in lowland, montane, and freshwater swamp forests throughout Sumatra. There are an estimated 500 Sumatran tigers remaining in Sumatra, with approximately 100 found in Gunung Leuser National Park in northern Sumatra (Franklin et al. 1999).
Numerous primate species live in these forests, including the long-tailed macaque (Macaca fascicularis), pig-tailed macaque (M. nemestrina), and siamang (Hylobates syndactylus), Sumatra's largest gibbon. Other species common to these forests include squirrels, monitor lizards, estuarine crocodile (Crocodylus porosus), false gharial (Tomistomus schlegeli), and the endangered clouded leopard (Pardofelis nebulosa) (Whitten et al. 1987; Stone 1994).
The swampy grasslands and forests provide important habitat for many waterbirds, including herons, egrets, bitterns, pond herons, whistling ducks, pygmy geese, lesser adjutant (Leptoptilos javanicus), milky stork (Mycteris cinerea), and the rare white-winged duck (Cairina scutulata) (Stone 1994).
Less than a fifth of the original extent of natural habitat remains in this severely threatened ecoregion. There are three protected areas that extend into the ecoregion and cover 620 km2 (3 percent) of the ecoregion, but two of these are less than 200 km2 (table 1). Freshwater swamp forests have very fertile soils that are suitable for agriculture; therefore, this ecoregion has been intensively converted and exploited (Whitten et al. 1987). Very little of the remaining habitat is in an undisturbed state, including the areas inside nature reserves.
Table 1. WCMC (1997) Protected Areas That Overlap with the Ecoregion.
Protected Area Area (km2) IUCN Category
Sei Prapat Simandulang 60 PRO
Giam Duri [IM0160] 140 PRO
Way Kambas [IM0158] 420 II
Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.
Types and Severity of Threats
Way Kambas is one of the oldest reserves in Indonesia, declared in 1937, and was upgraded to a national park in 1989. It was established to protect important freshwater and lowland rain forest flora and fauna in southern Sumatra. Despite its long standing as a nature reserve and increased protection in 1989, most of its land has been degraded by human interference (Scott 1994).
The estuarine crocodile and the false gharial, once numerous in this ecoregion, have been decimated by hunting, both from fear of these animals and for their skins, although the estuarine crocodile is protected by law in Indonesia (Whitten et al. 1987). Large-scale logging has also occurred throughout this ecoregion, especially from 1968 to 1974, and concessions cover 17 percent of the remaining habitat. Several large fires (1972, 1974, 1976, 1982, 1998, and 2000) have also swept through this ecoregion, destroying large tracts of forest. Paperbark, a common secondary growth tree in freshwater swamps, has a bark that peels off to form a highly flammable soil cover, encouraging further burning (Whitten et al. 1987). Climax communities of this forest, which include 100-year-old dipterocarp trees, are extremely slow to regenerate (Whitten et al. 1987). Widespread illegal logging, regardless of logging concessions, has occurred throughout Indonesia since the economic crises and fall of the Suharto government in 1998. It is doubtful whether any pristine freshwater swamp forests still exist in Sumatra. If any do exist, they will be under intensive pressure in the coming years and probably will be gone within 10 years (Holmes, Essay 1; Holmes, pers. comm., 2000).
Justification of Ecoregion Delineation
Whitmore (1984) 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