Lowland dipterocarp forests
A prominent tree of the lowland forests of Borneo is the Borneo ironwood (Eusyderoxylon zwageri), also known as belian. Much sought after by the timber industry, this tree’s durable and dense wood does not need to be treated, and is in high demand for bridges, roof tiles and pillars for houses.
Other key species include the giant nyatoh (Palaquiumspecies) and kenari (Canariumodontophyllum). Strangler figs (Ficus species) are distinct elements of tropical forests. These plants typically wind themselves around their host tree, eventually covering and killing it. The size of their trunk can be truly awesome – the total circumference of a single mature strangler fig, including all its stems, can be over 10 metres. The fruit from these trees are a major food source for many animals.
The many faces of lowland dipterocarp forests
In areas below 150 metres, lowland dipterocarp forests often contain many trees from the legume family and massive strangler fig plants. Many aromatic kapur trees (Dryobalanops species) are found growing in the coarse, sandy soil on moderate slopes. These trees were once exploited for camphor.
As we move beyond 150 metres, the dipterocarp forests in some parts of Borneo contain a greater diversity of plants than the extreme lowlands, in addition to large timber trees and wild fruit trees.
Above 500 metres, it is possible to encounter one of the 17 species of Rafflesia. A plant which produces the largest flower in the world growing up to 1 metre diameter. At around 1,000 metres, coniferous trees (pine relatives) start appearing, and the dipterocarp forest gives way to montane forests.
Wildlife of the dipterocarp forests of Borneo
Other large mammals of these forests include a Sumatran rhinoceros subspecies (Dicerorhinus sumatrensis harrissoni) and the Borneo pygmy elephant (Elephas maximus borneensis).
Down on the ground and along the branches, some of the region's smaller mammals scurry about - including the mountain treeshrew (Tupaia montana), the Bornean black-banded squirrel (Callosciurus orestes) and Whitehead's pygmy squirrel (Exilisciurus whiteheadi).
The dipterocarp forests are the hunting ground of the leopard cat (Cynocephalus variegatus), while proboscis monkey (Nasalis larvatus) and the Bornean tarsier (Tarsius bancamus) can also be found.
The Dipterocarps – a family of giants
More than 270 species of dipterocarp trees have been identified so far in Borneo. Of these, 155 are endemic to the island – they occur nowhere else in the world. In a sample plot at Wanariset, East Kalimantan, 30 species of dipterocarp were found; similar plots in North Sumatra yielded 12 species.
A striking characteristic of the Dipterocarp family is how rarely and irregularly they flower. Flowering only occurs once or twice every 10 years, sometimes longer. It usually happens at the same time as other trees in the same area.
The reason this happens is because of the El Niño Southern Oscillation (ENSO) – a natural climatic event that begins in the Pacific Ocean.
In Borneo, ENSO conditions not only trigger dipterocarp flowering, but also seem to have an influence on seed production. This phenomenon is seen as critical for forest regeneration, with dipterocarp species reported to synchronize their flowering over very large areas.