If you thought dipterocarp was the name of the huge herbivorous dinosaur that dwarfs the awestruck visitors in the atrium of London’s Natural History Museum, it might be time to take a side trip west to the Royal Botanic Gardens in Kew.

Dipterocarps are plants. But that description does them a gross disservice – a bit like labelling a whale shark simply as a fish, or referring to rafflesia as a flower.

The botanical equivalent of charismatic megafauna, dipterocarps are the skyscrapers of the forest. Several species attain heights well in excess of 80 metres. Their roots do not penetrate deep into the ground, since the nutrient-rich layer of rainforest soil is relatively shallow, so the tall trunks derive their stability from buttress roots that splay out sideways and snake across the forest floor.

Buttress roots such as these help prevent towering, shallow-rooted dipterocarp trees from toppling over. Credit: Alex Hyde/NaturePL

Their name – literally meaning two-winged fruit – derives from their huge and highly distinctive seeds, which rely on wind power to ensure that enough of them fall to the ground well beyond the patch of shade cast by the wide umbrella of the parent tree’s canopy.

Dipterocarps are distributed across the tropical regions of South America, Africa and Asia, but are most closely associated with the rainforests of Southeast Asia, where they are the dominant family of trees. In some cases, they comprise up to 90% of the canopy layer.

Why are dipterocarps important?

These colossal trees are the keystone species of their forest domain. They feed, shelter and support myriad other life forms, and lock up prodigious quantities of carbon in their roots, trunks and foliage. Natural allies in the fight against climate change, they make a massive contribution to carbon sequestration.

Individually and collectively, dipterocarp trees play a crucial ecological role: their roots hold together the soil; their trunks are natural highways; their leaves provide food and nutrients for other plant growth on the forest floor; their seeds feed terrestrial herbivores; and their canopy provides nest sites and temporary refuges, permanent homes for arboreal animals, a platform for epiphytic plants and fruit-bearing strangler figs, and acts as a giant umbrella, shielding the forest floor from the torrential tropical rain that would wash away soil and essential nutrients.

The distinctive winged seed of a dipterocarp, falling to the ground. Credit: Cyril Ruoso/NaturePL

Why are dipterocarps threatened?

Many dipterocarp species also have considerable cultural or economic value, and the latter has contributed to their downfall. Highly prized for their timber, dipterocarps have been decimated throughout their range, and only the least accessible and best protected trees have survived the logging onslaught. As a result, many dipterocarp species are threatened with extinction.

Fauna & Flora International (FFI) and our partners across the globe are working to save some of the world’s most threatened tree species, including a dozen dipterocarp species that are in dire need of conservation attention.

Dedicated to dipterocarps

Arief Hamidi, national botanist with FFI’s Indonesia programme, is a massive fan of these massive trees. His work across our project sites throughout the Indonesian archipelago focuses on rare, threatened and endemic trees (including a number of critically endangered dipterocarps), as well as native species with significant value to communities.

Arief at the base of a massive Anisoptera, another threatened dipterocarp species. Credit: Arief Hamidi/FFI

“Many dipterocarps are really on the brink of extinction and few people are aware of this. The challenge is to highlight these issues and invite decision-makers to take action. I really hope that these species have a future and that we succeed in protecting their habitat and reviving the population.”
Arief Hamidi FFI National Botanist, Indonesia

One such tree, known locally as pelahlar – scientific name Dipterocarpus littoralis – is found only on Nusakambangan, a small prison island off the coast of Java that has become an unlikely haven for some of Indonesia’s rarest wildlife.

Limited human settlement has meant that Nusakambangan retains around 75% of its original forest cover. Nevertheless, these forests haven’t escaped the attention of loggers seeking to exploit the island’s trees. Like other dipterocarps, pelahlar is highly prized for its timber. The large, branchless trunk makes it ideal for boat building and it has long been harvested to support this industry.

At one stage, there were thought to be fewer than 50 of these trees left in the entire world. Arief was a member of the 2014-15 survey team comprising staff from FFI’s Indonesia Programme and the local Conservation Department (BKDSA) that discovered a number of new pelahlar specimens, increasing the known global population to 149 mature trees.

A fallen leaf from the critically endangered pelahlar tree. Credit: David Gill/FFI

With so few trees left in the wild, monitoring and protection of the remaining population is paramount. Seed propagation could also provide a vital safety net for the species and produce saplings to boost restoration of the degraded forest. But the pelahlar takes many decades to reach full maturity, so it will require a long-term commitment to ensure the future of this critically endangered tree.

Arief is also intimately associated with two other critically endangered dipterocarp species, Dipterocarpus cinereus and Hopea bancana, both of which are found only one small island – Mursala – off the north-west coast of Sumatra.

D. cinereus was believed to be extinct until it was rediscovered in 2012. Even now, only three small subpopulations survive on the island. Arief joined a survey team aiming to estimate the population of the remaining stands of this super-rare dipterocarp, which clings to survival on Mursala’s virtually inaccessible hilltops. In total, just 30 mature trees were recorded, along with hundreds of saplings, confirming that the species is in urgent need of conservation attention.

The situation for Hopea bancana, which is also endemic to Mursala, is even more precarious. The most recent survey – again involving Arief – recorded a mere nine mature individuals among a total of 36 trees. The entire world population of this disappearing dipterocarp is confined to an area less than 16 square kilometres in extent, with timber extraction an ever-present threat to its survival.

Arief alongside a mature specimen of the critically endangered dipterocarp, Hopea bancana. Credit: Arief Hamidi/FFI

Why does this matter?

These are keystone species: the clue is in the name. Their disappearance would spell disaster for the wider forest ecosystem. Leaving aside their intrinsic economic and cultural value, and their crucial ecological importance, these trees also have a symbolic significance.

A tropical rainforest without giant dipterocarps is like an ocean without whales or an African savannah devoid of elephants. When we say that every species matters, we mean every species. At a time when biodiversity loss threatens the very fabric of our existence, we can ill afford to shrug our shoulders and turn away as the last of these forest giants crashes to the ground.