Some of the world’s largest and eldest rainforest areas are located in Borneo. The lush rainforest is home to the orangutan, which today only lives in isolated fragments comprised of mainly lowland areas but also including more hilly or mountainous areas (up to 1000 m). It has been estimated that the habitat of orangutans was around 25 million ha back in 1973, and will diminish to less than 10 million ha by 2025. This constitutes a loss of more than 15 million ha (62 %) in just about 50 years.
Orangutans favored home is primary tropical rain forest and old secondary forest at low elevations, though they may also venture into grasslands, cultivated fields, gardens, young secondary forest, and shallow lakes. The highest densities of orangutans are found in areas containing a mosaic of different habitat types that provide high quantities of food throughout the year such as peatlands, where tree diversity is high. Density declines significantly with increasing altitude, and Bornean orangutans have not been discovered at elevations greater than 1000 m.
Climate and variability
The temperature on Borneo varies throughout the year between 18° C to 38° C, with a relative constant humidity of 80 %. A calendar year can be divided into two seasons: the rainy and dry season, beginning in november and april, respectively. The rainfall varies greatly between years, as it is influenced by the strength of the Asian monsoon and the occurrence of El Nino/La Nina events. This in turn impacts the availability of fruits, which highly variable nature means that Bornean orangutans (as frugivores) must have a highly flexible diet as well. Read how climate change might affect the orangutan's habitat here >>
Highly productive forests
The two major types of forest on Borneo are peatland forests and lowland dipterocarp forest, which both provide prime habitat for the orangutan.
● The lowland dipterocarp rainforest
The dipterocarp rainforests can be highly productive, especially during large-scale fruiting events, occurring every two to 10 years. During these periods large numbers of trees fruit simultaneously and the orangutans consume fruit in amounts greatly exceeding their daily caloric need, thereby putting on additional storages of fat. However, the dipterocarp forests is also highly valued as timber resources, making the home of the orangutans especially vulnerable to large-scale logging. Read more about logging here >>
● The indispensable peatland forests
The peatland forests is a preferred home of the orangutan, due to the steady, all year around supply of prime orangutan foods. The nutrient-rich peat soil in the lowland forest areas also absorbs and stores large amounts of CO2, and regulates and purifies the water. However, vast amount of peatlands are each year burned for the conversion into agricultural plantations, typically oil palm or pulpwood. As peatlands contain up to 20 times more CO2 than normal rainforest, its destruction is amplifying the consequences of climate change. Read more about peatland here >>