The Borneo rainforest is the oldest rainforest in the world, and one of the most biodiverse.
There are about 15,000 species of flowering plants with 3,000 species of trees (267 species are dipterocarps), 221 species of terrestrial mammals and 420 species of resident birds in Borneo. It is also the center of evolution and radiation of many endemic species of plants and animals. Subject to mass deforestation, the remaining Borneo rainforest is one of the only remaining natural habitat for the endangered Bornean Orangutan. It is also an important refuge for the Asian Elephant, the Sumatran Rhinoceros, the and the Bornean Clouded Leopard.
There are seven distinct ecoregions in Borneo. The Borneo lowland rainforests cover most of the island, with an area of 427,500 square kilometres (165,100 sq mi). Other lowland ecoregions are peat swamp forests, freshwater swamp forests, and mangrove forests. The Borneo mountain rainforests lie in the central highlands of the island, above the 1,000 meters elevation. The highest elevations of Mount Kinabalu include the Kinabalu mountain alpine meadow, an alpine shrubland notable for its numerous endemic species, including many orchids.