Island of Borneo, Indonesia

The Southern Borneo Freshwater Swamp Forests [IM0153] can range in species diversity from numbers rivaling those of neighboring lowland rain forests to single-species forest stands of the Mallotus tree. Many of the animals that use lowland rain forest also use freshwater swamp forest, including all monkey and ape species. Like all other freshwater swamps found in the Indo-Pacific region, this ecoregion has been intensively converted to agricultural and plantation lands. Further protection is urgently needed to stem the loss of this ecoregion's native vegetation.

  • Scientific Code
  • Ecoregion Category
  • Size
    14,200 square miles
  • Status
  • Habitats

Location and General Description
This ecoregion is made up of the freshwater swamp forests in Kalimantan. These forests are located just inland from the southwestern coast, with a few small areas towards the center of the island. They are associated with coastal swamps, inland lakes, and low-lying river basins. Based on the Köppen climate zone system, this ecoregion falls in the tropical wet climate zone (National Geographic Society 1999).

Freshwater swamp forests exist where rivers meander through flat, low-lying alluvial floodplains before encountering mangrove forests. They are periodically flooded or waterlogged by mineral-rich fresh water, have a high pH (above 6), and do not contain substantial amounts of peat (Payne et al. 1994; FAO 1981). These factors combine to produce taller, more species-rich and more productive forests in comparison with peat swamp forests. The floristic composition of these forests is quite varied. They may include floating grass mats, the spiny pandan and palm vegetation, marshes, scrub, and forests. Mature freshwater swamp forest has an average tree height of 35 m, some lianas, and numerous epiphytes (Payne et al. 1994; MacKinnon et al. 1997).

Freshwater swamp forests can range from species-poor stands dominated by the genus Mallotus to forests that are floristically diverse. The flora is not distinct but may contain many species common in the surrounding lowland rain forest. The commonly occurring genera include Adina, Alstonia, Campnosperma, Coccoceras, Dillenia, Dyera, Erythrina, Eugenia, Ficus, Gluta, Lophopetalum, Memecylon, Metroxylon, Pandanus, Pentaspadon, Shorea, and Vatica (FAO 1981). The tall legumes Koompassia, Calophyllum, and Melanorrhoea and the swamp sago Metroxylon sagu also thrive in this habitat (MacKinnon 1997).

Biodiversity Features
The faunal diversity and abundance vary with the structure and diversity of the vegetation in the forest but are usually higher than in peat swamp forests. Primate densities in freshwater swamp forests can be as high as in lowland rain forests. Like peat swamp forests, they are usually the highest around rivers. Long-tailed macaques (Macaca fascicularis) are the most common primates in freshwater swamp forests. Long-tailed macaques are the most adaptive primate found in Borneo and can live almost anywhere. They are found in rain forests, mangrove forests, freshwater forests, disturbed or logged forest, or even human-dominated landscapes such as villages. These monkeys live in troops of twenty or more and are commonly seen in coastal areas wandering over the beach searching for food. This behavior has earned them an alternative name: the crab-eating macaque (MacKinnon et al. 1996). In inland riverine swamp forests, they are primarily frugivorous, with leaves, flowers, insects, and bark providing the remainder of the diet (Yeager 1996).

These forests are also home to the endangered orangutan (Pongo pygmaeus). The orangutan is a CITES I species and was added to the U.S. Endangered Species list in 1970. Despite these efforts, the populations of orangutans in both Borneo and Sumatra have continued to diminish, primarily through habitat loss and poaching (for food or the pet trade) (Yeager 1999). Orangutans have adapted to both tropical forest and freshwater swamp forests. Orangutans' primary food is fruit, but they also feed on a complex mix of nuts, leaves, insects, bark, honey, and sap. Orangutans often visit numerous trees as their fruit becomes ripe over wide areas, keeping track of dozens of fruiting trees. As the trees drop their last fruit, they move on to other tree species (notably figs). In this way orangutans act as seed dispersers for numerous tree species (Galdikas and Briggs 1999).

The bird fauna numbers more than 360 species and includes a wide variety of hornbills and a single near-endemic species the Javan white-eye (Zosterops flavus) (table 1).

Table 1. Endemic and Near-Endemic Bird Species.

Family Common Name Species
Zosteropidae Javan white-eye Zosterops flavus

An asterisk signifies that the species' range is limited to this ecoregion.

Current Status
Most of the original vegetation of the freshwater swamp forests has been cleared or modified by human activity. Only about 1.4 percent of the original land area is still forested; the rest has been cleared away for agriculture, especially sawah rice (MacKinnon et al. 1996). The existing protected area system, consisting of nine reserves, covers 3,520 km2 (10 percent) of the ecoregion area (table 2). There are several reserves (including those that extend into the ecoregion) that are more than 500 km2. The Tanjung Puting National Park provides some of the best freshwater habitat for orangutans and other wildlife in Borneo. However, this park, like the majority of parks and reserves in Indonesia, has been subject to severe encroachment by illegal loggers and illegal gold mining in the past few years (Yeager, pers. comm., 2000).

Table 2. WCMC (1997) Protected Areas That Overlap with the Ecoregion.

Protected Area Area (km2) IUCN Category
Muara Kendawangan [IM0104], [AA0124] 720 PRO
Unnamed [AA0124] 90 ?
Tanjung Penghujan NR [AA0124] 110 PRO
Tanjung Puting [IM0104], 90, 110] 660 II
Bukit Tangkiling 50 I
Danau Semayang Sungay Mahakam [IM0145] 900 PRO
Kutai [IM0161], [IM0143] 110 II
Kutai (extension) [IM0104], 90, 97] 430 PRO
Muara Kaman Sedulang [IM0104], [IM0161] 450 I
Total 3,520  

Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.

In 1997 and 1998 El Niño-driven fires burned through large portions of Sumatra and Borneo. Most of these fires were intentionally set to clear forest for large commercial oil palm plantations. Preliminary estimates indicate that more than 7,500 km2 of both freshwater and peat swamp forests were lost during these fires. The subsequent years of 1999 and 2000 saw further forest loss. The effects on the forest's wildlife populations were profound. The fires of 1997-1998 exceeded many species' ability to adapt to the loss of habitat and stress of lost food sources. Hundreds of adult orangutans were killed as the fled the fires and encountered human populations. Many of the orphaned juveniles were then sold into the international pet trade (Barber and Schweithelm 2000).

Types and Severity of Threats
The primary threat to this habitat is deforestation caused by conversion of forests to plantations, slash-and-burn agricultural practices, uncontrolled fires, mining, and exotic species. Fires are set in freshwater swamp forests to make room for plantation crops such as oil palm and pepper. This trend is not likely to abate given the current economic and political situation in Indonesia.

Freshwater swamp forests are highly desirable to commercial timber operations because of their high stocking level of commercially valuable species. The soil in most of the deep alluvial terraces is deep, fertile, and well watered, promoting rapid forest growth. However, it is also ideal for agriculture, and this ecoregion has been intensively cleared for cultivation (MacKinnon et al. 1996). In south and southeast Kalimantan, original freshwater swamp forests were converted to single-species stands of paperbark (gelam) (Melaleuca cajuputi), sedge and swamp grass, or wet rice fields (Whitmore 1984). Paperbark is a fire-adapted species with thick, fire-resistant bark. During repeated burns or uncontrolled fires paperbark regenerates quickly, outcompeting and eradicating most native species. Paperbark is used extensively by local people for cajeput oil, insect repellant, soap, caulking for boats, firewood, and construction (Brinkman and Xuan 1986; Klepper et al. 1990). The wide variety of uses derived from this tree promote its wider distribution into additional freshwater swamp forests.

Another increasing threat to the forest integrity is the lure of gold. Gold accumulates in the alluvial fans, and Indonesia is rapidly becoming one of the world's leading gold exporters. Most of the mining operations are illegal and use water pumps and mercury to separate out the gold. This causes increased sedimentation in the rivers and bioaccumulation of heavy metals in numerous riverine species (Galdikas and Briggs 1999).

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 et al. 1996). MacKinnon and MacKinnon (1986) divided the island's lowland forests into six subunits, with a central subunit representing the montane forests. MacKinnon (1997) revised the boundaries of these seven subunits but retained the same general configuration. These authors 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 (MacKinnon and MacKinnon 1986; MacKinnon 1997).

Because ecoregions are based on biomes, we first isolated the central montane ecoregion-the Borneo Montane Rain Forests [IM0103]-above the 1,000-m elevation contour using the DEM (USGS 1996). We then assigned the large patches of peat forests, heath forests, freshwater swamp forests, and mangroves, in the lowlands and along the periphery of the island, into their own ecoregions: the Borneo Peat Swamp Forests [IM0104], Sundaland Heath Forests [IM0161] (which also includes Belitung Island and the heath forests in Bangka island), Southern Borneo Freshwater Swamp Forests [IM0153], and Sunda Shelf Mangroves [IM1405], respectively. The alpine habitats of the Kinabalu Mountain Range were represented by the Kinabalu Montane Alpine Meadows [IM1001].

References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List

Prepared by: Colby Loucks
Reviewed by: