Location and General Description
This ecoregion is made up of the lowland dipterocarp forests of Borneo. All of Borneo, Java, Sumatra, and mainland Malaysia and Indochina were once part of the same landmass during the Pleistocene glacial period. Land bridges connected all of these islands, fostering waves of migrations of animals, plants, and humans (MacKinnon 1997). Today Borneo is separate but shares similarities in flora and fauna with these other landmasses. The geology of the Borneo Lowland Rain Forests [IM0102] consists of limestones, volcanic rocks, schist-gneiss complexes, and sedimentary rocks. Soils are primarily ultisols and inceptisols, generally older, infertile soils (RePPProT 1990). Based on the Köppen climate zone system, this ecoregion falls in the tropical wet climate zone (National Geographic Society 1999). Monthly rainfall exceeds 200 mm year-round, and the temperature rarely fluctuates more than 10°C.
The natural vegetation of this ecoregion is tropical lowland rain forest. The region's stable climatic conditions have given rise to some of the world's richest assemblage of flowering plants. Forests contain a high diversity of tree species, and dominant species are uncommon. As many as 240 different tree species can grow within 1 ha, with another 120 in the hectare adjacent (Kartawinata et al. 1981; Ashton 1989). The general characteristics of these forests are canopies 24-36 m high, with emergents reaching up to 65 m. Dipterocarpaceae is a dominant family in the emergent stratum (Whitmore 1984). In the richest forests, up to 80 percent of the emergent trees are dipterocarps, although the white-barked Koompassia tree (Laurelaceae) is a readily identifiable emergent as well. Of the dipterocarp genera, Dipterocarpus, Dryobalanops, and Shorea are the emergents, and Hopea and Vatica usually are found in the main canopy. Berseraceae and Sapotaceae are other common main canopy families (MacKinnon et al. 1996). Bornean ironwood (Eusideroxylon zageri), or Belian, is a common and commercially valuable species. A third layer occurs below the canopy of shade-tolerant species, adorned with lianas, orchids, and epiphytic ferns. This layer includes many species from the Euphorbiaceae, Rubiaceae, Annonaceae, Lauraceae, and Myristicaceae families. In some cases Euphorbiaceae is more common than dipterocarps, being the second most common family in Borneo (Newberry et al. 1992). Another unique feature of this layer is the prevalence of caulifory. Caulifory is a phenomenon in which trees bear their flowers and fruits on their trunks. The forest durian (Durio testudinarum) is a common example of caulifory. On the forest floor, herbs, seedlings, and shade-tolerant palms exploit the few places that receive sunlight.
Limestone formations are found throughout Borneo and include extensive areas in the Sangkulirang Peninsula and the limestone hills of Sarawak. Detailed botanical surveys of the limestone areas have not been completed, but preliminary studies suggest that this habitat supports a tremendous number of flora species, many of them probably endemic (Whitmore 1989). Although limestone forest has little commercially valuable timber, herbs such as Balsaminaceae, Begoniaceae, and Gesneriaceae (which are well represented in this ecoregion) have horticultural potential (Whitmore 1989). The Labi Hills of the Brunei-Sarawak border support a diverse mosaic of forests on podzols and sandy yellow soils, and these are rich in endemics, including two palms, Livistona exigua and Pinanga yassinii, known only from podzolized ridges in the Ulu Ingei area (WWF and IUCN 1995). There seems to be no special vertebrate fauna associated with limestone in this ecoregion, although banteng (Bos javanicus), orangutan (Pongo pygmaeus), Bornean gibbon (Hylobates muelleri), sambar (Cervus unicolor), muntjac (Muntiacus muntjak), and mousedeer (Tragulus spp.) all use limestone outcroppings (MacKinnon et al. 1996).
The flora of Borneo alone consists of about 10,000-15,000 species, more than on any other island or region in Malesia and richer than all of Africa, which is forty times larger (Burley 1991; Jacobs 1988). Borneo has more than 3,000 tree species and 2,000 orchid species and is the center of distribution of dipterocarps, with 267 species, 60 percent of them endemic (Ashton 1982; Whitmore and Tantra 1987). Some of the most unique plants in the world are the five or six species of the parasitic Rafflesia plant found in Borneo. All Rafflesia produce large brown, red, orange, and white flowers. The largest in the world, Rafflesia arnoldii, is found in this ecoregion and produces flowers more than 3 feet wide. Rafflesia have no leaves, instead deriving all their energy from the tissues of the ground vine Tetrastigma, which it parasitizes. Large buds emerge from the vine and have five petals that surround spikes that smell like rotting meat. This smell attracts insects, which act as pollinators (MacKinnon et al. 1996).
Bornean rain forests share much of their fauna with the Asian mainland and other Sunda islands but few with Sulawesi and the eastern islands. The wildlife in the Bornean lowland rain forests is not characterized great spectacles of migrating or large charismatic species but by an enormous diversity of forest animals. As a whole, Borneo has a higher number of endemic mammals (forty-four) than the other islands in the Sunda Shelf and Philippines Bioregion, but fifteen are limited to lowland forests, and many of these are small rodents and bats (MacKinnon et al. 1996). Twelve of these are endemic, and one is near endemic to these forests (table 1).
Table 1. Endemic and Near-Endemic Mammal Species.
Borneo also lacks some of the larger predators found in Asian mainland ecoregions, such as the tiger (Pantera tigris) and the leopard (P. pardus). In their absence, several small-medium carnivores dominate these forests, including the endangered clouded leopard (Neofelis nebulosa), sun bear (Helarctos malayanus), Sunda otter-civet (Cynogale bennettii), and other mustelids (MacKinnon 1997). The Asian elephant (Elephas maximus) and critically endangered Sumatran rhinoceros (Dicerorhinus sumatrensis) are found in northeastern Borneo. The Asian elephant and Sumatran rhinoceros are the largest forest herbivores, and they need a large amount of forest to survive. The intense human pressure on the natural forests will challenge their ability to survive in the long term.
Borneo's lowland forests are home to the globally recognized orangutan. The prehistoric race of orangutan distribution reached mainland Asia through Indochina and Thailand to southeastern China. Today the orangutan is limited to northern Sumatra and Borneo (Galdikas and Briggs 1999). Unlike other apes, orangutans are solitary and arboreal. They feed primarily on fruit but also feed on leaves, flowers, insects, and, during times of food stress, specifically bark (Knott 1998). The orangutans move throughout the forest, following the fruiting of numerous trees. They have the ability to catalog the location and degree of a fruit's ripeness for a large number of trees and species (Daws and Fujita 1999; Galdikas and Briggs 1999).
The orangutan is not the only primate in Borneo's lowland forests. They are home to thirteen primate species: three apes (the orangutan and two gibbon species), five langurs, two macaques, the tarsier (Tarsius bancanus), the slow loris (Nycticebus coucang), and the endangered proboscis monkey (Nasalis larvatus). Most of these species have overlapping ranges, but they vary with respect to dietary content and foraging strategy (MacKinnon 1997).
The fauna communities are divided into those that are active during the day and those that are nocturnal. Orangutans, pig-tailed macaques (Macaca nemestrina), and the white-rumped shama (Copyschus malabaricus), with its melodious calls, can be seen or heard during the early part of the day. Many birds, reptiles, and amphibians browse throughout the day. As night approaches, bats such as the large flying-fox (Pteropus vampyrus) and flying squirrels begin to appear. Pangolins (Manis javanicus) search for ants on the forest floor, while civets and the clouded leopard (Neofilis nebulosa) hunt for food. Bearded pigs, though occasionally active during the day, are predominantly nocturnal animals. The tarsier (Tarsius bancanus), one of Borneo's strangest animals, with its large eyes searches out smaller animals and leaves for food.
The bird fauna, like the mammal fauna, is similar to that of peninsular Malaysia and Sumatra. In Borneo there are eight hornbill species, eighteen woodpecker species, and thirteen pitta species. The 385 bird species attributed to the ecoregion include nine near-endemic species and two endemic species: the black-browed babbler (Malacocincla perspicillata) and the white-crowned shama (Copsychus stricklandii) (table 2). Hornbills such as the bushy-crested (Anorrhinus galeritus), helmeted hornbill (Rhinoplax vigil), and great rhinoceros (Buceros rhinoceros) are important seed disperses of many fig (Ficus spp.) trees. Figs act as a keystone resource, providing food for many animals such as monkeys, arboreal mammals, squirrels, civets, and birds. The high diversity of fig trees in the rain forest assures food during fruiting throughout the year (MacKinnon et al. 1996).
Table 2. Endemic and Near-Endemic Bird Species.
Borneo is probably the richest island in the Sunda Shelf for reptile and amphibian diversity. Because detailed studies of the entire island have not been done, an incomplete picture emerges. For example, the earless monitor lizard (Lanthonotus borneensis) spends most of its life in underground caves and has been recorded in only a few places in Borneo. However, it probably has a widespread distribution throughout the island. Many populations of amphibians and reptiles are also hunted toward the brink of local extinctions.Current Status
This ecoregion is the second largest ecoregion in the Indo-Pacific region, yet more than half of the natural habitat in this ecoregion has been cleared or degraded. In recent years there has been extensive habitat loss, and current assessments predict further widespread destruction of forests. There are sixty reserves on paper that protect almost 12 percent of the region, but many are small (less than 100 km2) or are still proposed (table 3). Only six reserves have been gazetted that protect more than 1,000 km2 of contiguous lowland rain forest. The remaining reserves are proposed. These include Gunung Bentuang, Kutai, Pleihari Martapura, S. Kayan S. Mentarang, Tabin, and one SAR (Sanctuary Reserve). The protection of these reserves and the gazetting of the proposed reserves are essential to the conservation of biodiversity in this ecoregion.
Table 3. WCMC (1997) Protected Areas That Overlap with the Ecoregion.
This area has been heavily logged, with most logging occurring in the last thirty years. Commercial logging destroyed the forests while providing access to them. Massive agricultural projects, such as oil palm, rubber, and industrial timber for pulp and plywood, soon followed. Smaller agricultural shareholders also filled in these areas by cutting and burning patches of forests. By the late 1980s Indonesia was the world's largest plywood producer. Private and state-owned forestry companies have stripped the land clear for pulp and palm oil plantations, destroying vast tracts of forest. They are replanting with a limited number of fast-growing exotic species (Galdikas and Briggs 1999; Barber and Schweithelm 2000).
In 1982-1983 27,000 km2 of tropical rain forest was burned in Kalimantan. The cause of what was at the time the largest forest fire ever recorded was widespread logging activities over the previous decade. Logging had transformed the fire-resistant primary forest into a degraded and fire-prone landscape. The El Niño-driven drought of that year set that stage for catastrophe when small agricultural fires escaped and ignited the forest (Grip 1986).
Indonesia did not learn from its past lessons. In 1997-1998, another intense El Niño year, the same events unfolded. In 1997-1998 fires raged across Kalimantan and Sumatra as forests were being cleared to make way for agriculture and plantation lands. More than 23,750 km2 of lowland rain forest in Kalimantan was burned in these years alone. Primary tropical rain forests do not burn naturally, so few native plant or animal species are adapted to fire. Fires in pristine forests rarely escape the ground vegetation because of the high humidity and moisture. However, tropical rain forests that have been previously logged are fire-prone because large amounts of wood are left on the forest floor, and the forest canopy is opened, drying out the ground vegetation. These forests rarely escape fires such as those set throughout Indonesia in 1997 (Holmes, Essay 1; Barber and Schweithelm 2000; Yeager 1999a).
The prognosis for Borneo's lowland forests is bleak. With little to no law enforcement in Indonesia, large tracts of land will be susceptible to burning every year by commercial logging agricultural projects such as oil palm, rubber, and industrial timber for pulp and plywood. Smaller agricultural shareholders threaten the forests through continued slash-and-burn agricultural practices. Little to no regard is given to the long-term environmental effects these actions will cause. Without immediate intervention to stem the loss of these forests, and given the current rate of destruction, there will be no primary lowland dipterocarp forests remaining in Indonesian Borneo within ten years.
The current system of protected areas underrepresents the habitat, and, based on the actions from 1997-1998, even protected areas will become susceptible to illegal and rampant logging and burning activities. The loss and fragmentation of the forest habitat will have drastic effects on the wildlife populations. As the forests shrink, more and more primates will interact with humans, and many will be killed or sold into the international pet trade. Vast numbers of species will become extinct before they have even been described and their role in the ecosystem determined. This collapse of the ecosystem will occur long before the last dipterocarp is cut down or set afire.
Exploration for oil and coal is a potential major threat to Gunung Lotung and the Maliau Basin in south central Sabah (WWF and IUCN 1995). On the Klias Peninsula, proposed development schemes will drain the wetlands for agriculture and pose the most serious threat (WWF and IUCN 1995).
Justification of Ecoregion Delineation
The large island of Borneo was divided into seven 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 mammal species 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]. The remaining lowland dipterocarp forests in Borneo were combined into one ecoregion, Borneo Lowland Rain Forests [IM0102]. This deviates from MacKinnon's use of subunits (25a, b, f, g, h, i) to divide Borneo.
References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
This text was originally published in the book Terrestrial ecoregions of the Indo-Pacific: a conservation assessment from Island Press. This assessment offers an in-depth analysis of the biodiversity and conservation status of the Indo-Pacific's ecoregions.
For more general information on this ecoregion, go to the WildWorld version of this description.All text by World Wildlife Fund © 2001