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Sulawesi

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The Sulawesi lowland rain forests harbor some of the most unique animals on Earth. The islands are located in the region known as Wallacea, which contains a distinctive fauna representing a mix of Asian and Australasian species. A fruit-eating pig with huge tusks, a dwarf buffalo, endemic macaques, and cuscuses exemplify a truly unique mammal community. Sulawesi, like the hub of a wheel, is surrounded by a variety of exotic ocean basins, including the Flores Sea, the Banda Sea, the Molucca Sea, the Java Sea, and the Straits of Makassar, as well as the diverse islands of Borneo, Java, Flores, Halmahera, and the Philippines. More than half of the original forest has been cleared, and most of the remaining forests have been reduced to fragments.

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Location and General Description

This ecoregion represents the lowland forests (less than 1,000 meters (m)) on Sulawesi and the surrounding islands of Banggai and Sula to the east and Talaud and Sangihe to the north. Sulawesi is almost completely mountainous. There are no extensive lowlands on Sulawesi, with large areas above 1,000 m and the highest elevation at 3,455 m on Mt. Rantemario. Sangihe is mountainous, reaching an elevation of 1,784 m, whereas Talaud is low-lying. The physiography of the Sula Islands is hilly, with mountains over 800 m only on the island of Taliabu.

The upland areas (more than 1,000 m) of Sulawesi form a separate ecoregion, the Sulawesi montane rain forests. Based on the Köppen climate zone system, this ecoregion falls in the tropical wet climate zone. Sulawesi has a complex geologic history and is composed of three geologic provinces based on that history. West and East Sulawesi form two of the geologic provinces, separated by the Palu-Koro fault, which runs from the town of Palu to the Gulf of Bone. The third geologic province consists of the Tokala region on the northeast peninsula, the Banggai Islands, Butung Island, and the Sula Islands. East and West Sulawesi collided approximately 13-19 million years ago, and ultrabasic rocks were exposed as East Sulawesi overrode the western portion. The forces that caused the collision are still at work, and Sulawesi is being torn apart today. The surface geology of Sulawesi is a diverse patchwork of ophiolites, Mesozoic sedimentary rocks, Tertiary sedimentary and igneous rocks, and Quaternary volcanics and sediments. Active volcanoes are located on the northern arm of Sulawesi.

The lowland forest is predominantly tropical lowland evergreen and semi-evergreen rain forest, with some monsoon forests at the tip of the southeast peninsula and small areas of freshwater and peat swamp forest. Distinctive forest types on limestone are distributed around southern Sulawesi and on ultrabasic soils in scattered locations all around the island. The lowland and hill forests contain the most tree species, although these forests are not dominated by any one tree family; only seven dipterocarp species are found in Sulawesi (compared with 267 and 106 in Borneo and Sumatra, respectively). The dipterocarps include Anisoptera costata, Hopea celebica, H. gregaria, Shorea assamica, Vatica rassak, and V. flavovirens. Distinctive ebonies (Diospyros spp.) were common in dense clumps in the lowland forests. Palms are common in the lowland forest, including Oncosperma horridum, Liculala celebensis, Pinanga, Areca, Caryota, and Livistona rotundifolia.

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The isolated Sula Islands, just off Sulawesi's east coast, receive rain from both the northwest and the southeast and have volcanic soils that create excellent growth conditions.

Aopa Swamp, 100 kilometers (km) west of Kendari, is a major area of peat swamp that varies seasonally in extent from about 150 to 314 square-kilometers (km2). The dominant tree species in this forest include Casuarina spp., Eugenia spp., Geunsia paloensis, Premna foetida, Metroxylon sagu, Pholidocarpus spp., Licuala spp., Arenga spp., Oncosperma spp., and Corypha spp. Sedges such as Scleria spp. also occur along with 5-m tall Pandanus spp., at least two species of climbing rattan, and epiphytic Lecanopteris ant-ferns.

Freshwater swamp forest is characterized by grassy areas near open water, with palms and pandans on firmer ground and ubiquitous pitcher plants (Nepenthes). Riverine forest dominated by tall Eucalyptus deglupta is found in the Sopu Valley northeast of Lake Lindu and Mt. Nokilalaki.

This ecoregion also includes karst (limestone) areas that have a relative paucity of trees and tree species because of their shallow soils and steep slopes, resulting from the high solubility of limestone rocks. High calcium levels in the soil give rise to distinctive tolerant plant communities but support certain snail species limited to limestone forest as well as the large swallowtail butterfly (Graphium androcles).

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Infertile ultrabasic substrates, with serpentine and peridotite rocks, contain unique forests with a high degree of plant endemism. Common species include ironwood (Metrosideros), Agathis, Calophyllum, Burseraceae, Sapotaceae, and dipterocarps (Vatica and Hopea celebica). Myrtaceae (Eugenia, Kjellbergiodendron, and Metrosideros) are dominant in the low and regular canopy. There is little marketable timber in such forests.