Borneo, a giant, rugged island in Southeast Asia’s Malay Archipelago, is shared by the Malaysian states of Sabah and Sarawak, Indonesian Kalimantan and the tiny nation of Brunei. It’s known for its beaches and ancient, biodiverse rainforest, home to wildlife including orangutans and clouded leopards. In Sabah is 4,095m-tall Mount Kinabalu, the island’s highest peak, and, offshore, the famed dive site Sipadan Island.
The island is bounded by the South China Sea to the northwest, the Sulu Sea to the northeast, the Celebes Sea to the east, and the Java Sea to the south—the latter separating Borneo from the island of Java. The Makassar Strait separates Borneo from the island of Celebes (Sulawesi) to the east and southeast, and a series of shallow seas and straits lie between Borneo and the island of Sumatra to the west.
Indonesia constitutes the largest political component of the island (in Indonesian known as Kalimantan), its territory divided into five provinces: Central Kalimantan, East Kalimantan, North Kalimantan, South Kalimantan, and West Kalimantan. Along the northwest coast and northern tip lie Sarawak and Sabah, two constituent states of Malaysia that are often collectively called East Malaysia, and between them is the Islamic sultanate of Brunei.
Borneo lies astride the Equator. It has a length of 830 miles (1,336 km) from northeast to southwest and a maximum breadth of 600 miles (960 km). The island is largely mountainous, although there are extensive lowlands, especially in Central Kalimantan and Sarawak, that are often swampy along the coasts.
A long series of mountain ranges extend southwest across the island from Mount Kinabalu in the far northeast, which, at an elevation of 13,455 feet (4,101 metres), is the island’s greatest height and is also the tallest peak in Malaysia. Ranges in the central spine include the Crocker, the Nieuwenhuis, and the Muller mountains. The Kapuas Hulu Mountains branch westward from the central core along the border between Sarawak and West Kalimantan, and a separate and discontinuous series of ranges parallel the east and southeast coasts in East and South Kalimantan.
Borneo’s climate is equatorial—hot and humid with a fairly distinct division into two seasons, consisting of a wet monsoonal period (landas) between October and March and a relatively drier, calmer period of summer (tedoh) for the rest of the year. The average annual rainfall is about 150 inches (3,800 mm).
Fauna and Flora
Borneo is largely covered in dense rainforest, and both the floral and the faunal populations of the island are extremely varied. There are extensive stands of teak, oak, conifers, and hardwoods of the Dipterocarpaceae family (including members the commercially valuable genus Shorea). The forests are also noted for their epiphytes and for the monster flower (Rafflesia arnoldii), the largest flower in the world.
Mammals endemic to the island include the Bornean clouded leopard (Neofelis diardi) and the proboscis monkey (Nasalis larvatus). Other notable animals include orangutans, gibbons, and elephants, but the Sumatran rhinoceros is now extinct there. There are also a great many species of birds, insects, and fish.