Sulawesi, with an area of 180,681 km², is the fourth-largest island in Indonesia, and the eleventh-largest in the world. The landmass of Sulawesi includes four peninsulas: the northern Minahasa Peninsula, the East Peninsula, the South Peninsula, and the Southeast Peninsula. The island is mountainous, and the highest peak is Mount Latimojong at 3,478 meters. Approximately 40% of Sulawesi's land area is in the montane rain forests ecoregion; the surrounding lowlands are in the Sulawesi lowland rain forests ecoregion. The islands that make up the ecoregion are part of Wallacea, a group of islands that are part of the Australasian realm, but were never joined to either the Australian or Asian continents. The islands of Wallacea are home to a mix of plants and animals from both terrestrial realms, and have many unique species that evolved in isolation. The Makassar Strait separates Sulawesi from Borneo to the west; the strait is part of the Wallace Line, which demarcates the western boundary of Wallacea. Borneo and the other Indonesian islands west of Sulawesi are part of Sundaland, and were connected to the Asian continent when sea levels were lower during the ice ages.
Climate
The ecoregion has a wet tropical montane climate.
Flora
The main plant communities are lower montane rain forest, upper montane rain forest, and sub-alpine forests. The forests generally form a closed canopy, and height decreases with elevation. Lower montane rain forest, or sub-montane forest, ranges from 1000 to 1500 meters elevation. Trees in the beech family are predominant, including four species of Lithocarpus and two species of Castanopsis. Other trees include Eugenia, along with trees in the myrtle family, laurel family, and tea family and the conifers Agathis dammara and Phyllocladus. Epiphytes including orchids are common. In the mid-montane forests Fagaceae, especially Lithocarpus menadoensis and L. celebicus, Myrtaceae, and Agathis are predominant. Upper montane forests are characterized by conifers, including species of Agathis, Podocarpus, Dacrycarpus, Dacrydium, and Phyllocladus, together with Myrtaceae and the shrubs Rhododendron, Vaccinium, Gaultheria, and Tasmannia piperita. Fagaceae are less common than in the lower-elevation forests. Mosses become abundant over 2000 meters elevation. Sub-alpine communities form above 3200 meters elevation, with low trees and shrubs, principally Rhododendron, Decaspermum, and Hedyotis, along with the lower shrubs Gaultheria and Styphelia suaveolens. The trees and shrubs are festooned with lichens. Herbs include the daisy Keysseria, the ginger Alpinia, Potentilla leuconata and P. parvus, and the grasses Poa and Agrostis.
Fauna
The ecoregion is home to 102 mammal species, a third of which are endemic or near-endemic. 24 mammal species are endemic to the ecoregion, and 10 are near-endemic. Larger mammals include two pigs, the Celebes warty pig and North Sulawesi babirusa. The Celebes warty pig lives in the lower montane and lowland rain forests of Sulawesi and other islands of Wallacea. The North Sulawesi babirusa lives in both the montane and lowland rain forests of northern and central Sulawesi. The endemic Mountain anoa is a dwarf buffalo which stands only 70 cm high. The Celebes rusa deer is a subspecies of the Javan rusa, which may have been introduced from Sundaland to Sulawesi by humans in ancient times. There are two endemic arboreal primates, Dian's tarsier and the Pygmy tarsier ''. The majority of endemic species are rodents, including three squirrels and 17 Murid rodents:
The Bola Batu babirusa, known only from bones, is recognized as a separate species. No living individuals have been recorded, and the species may be extinct. The ecoregion is home to 168 bird species. 19 species are endemic to the ecoregion, and another 23 are near-endemic.
Protected areas
A 2017 assessment found that 9,066 km² 12%, of the ecoregion is in protected areas.
