What are Dipterocarps?

Rainforests in the Sunda ecoregion are often referred to as lowland or highland dipterocarp forests - however, there is a paucity of awareness around the special origin of this name. Dipterocarps are a family of around 700 species of trees, gaining their name from the Greek "di" meaning two, ptero-", meaning wing, and "karpos", meaning fruit. Known for their characteristic, winged helicopter-like seeds, the Dipterocarps produce seeds with 2, 3, or 5 wings (despite the name). In healthy, unlogged Southeast Asian rainforests, they form the dominant family of trees, and form a popcorn-like canopy over thirty to sixty metres high!

A dipterocarp seed from the Shorea family (Source: berniedup)

Ecologically highly important, the canopy they form creates the layered structure of rainforests, and their fruits, flowers, and sap are an important food source for wildlife. An interesting feature of their ecology is that they fruit only one in two to five year (this is thought to be linked to the El Niño phenomenon), in a process called masting. The entire forest blooms simultaneously, producing a profusion of flowers and winged fruits - this is an extremely important ecological event in the Sunda rainforests, and can be life-saving for many species in dry weather conditions.

A mass flowering in Danum Valley (Source: UFZ)

Northern Borneo is the epicentre of diversity for these trees, and the worlds tallest tropical trees (over 95 metres tall!) are Dipetrocarps! (Shorea leprosula, to be precise). Their gum, dammar, was an important product historically, and the Borneo camphor tree, Dryobalanops aromatica, continues to be an important source of edible camphor for medicinal and culinary uses. Their strong, straight trunks have unfortunately made them an attractive source of timber, and they are logged heavily for this reason, decimating forests. However, they are often recalcitrant, which means that their seeds are only viable for a short period of time after fruiting, and require very specific conditions - this means that in logged forests, the harsh sunlight and dry soil will prevent Dipterocarp seeds from growing. As a result, tree diversity in many secondary forests is very poor, and often logged forests transition into seasonally burning grasslands. Dipterocarps anchor the ecosystem in place - in their absence, the rainforest quickly begins to unravel.

However, all hope is not lost. With nursery-grown dipterocarp trees, and a stage-wise planting process to create shade and leaf-litter from pioneer tree species, the original forest can begin to be re-created. At the Princeton Rainforest, we hope to establish a nursery to propagate these unique trees, and restore the lost glory of the rainforest. Stay tuned for updates!

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