What they are
The Dipterocarpaceae — the dipterocarps — are a family of mostly enormous tropical trees that dominate the rainforests of Southeast Asia as no single family dominates any other rainforest on Earth. In the forests of Borneo, Sumatra, Malaysia, and the region, dipterocarps make up the majority of the tallest trees, and the tallest tropical trees ever measured (over 100 m) are dipterocarps.
The name means "two-winged fruit," and it describes their most obvious feature: the nut-like seed is topped by long, stiff, papery wings — usually two, sometimes more — that make it spin like a helicopter or shuttlecock as it falls, slowing its descent from the great height of the parent so it drifts a little from the trunk. The seeds of maples and ash use the same winged, spinning trick in the temperate world.
The great mast flowering
Dipterocarps do something ecologically extraordinary that shapes the whole forest: they take part in general (mast) flowering.
Instead of flowering every year, the dipterocarps — and many other forest trees with them — stay vegetative for years, then, every two to seven years, and triggered by the drought and cooler nights of an El Niño event, they all burst into flower and fruit at once, across whole regions, in a synchronised, forest-wide event. For a few weeks the canopy is coloured with flowers and then rains down millions upon millions of winged seeds together.
The reason is predator satiation, the same strategy behind the beech and oak mast years: by producing almost no seed for years and then a colossal glut all at once, the trees overwhelm the seed-eating animals (which cannot build up their numbers on the lean years), so that far more seed survives to germinate than if the trees fruited a little every year. It is one of the grandest examples of reproductive synchrony in nature, and it means dipterocarp forests regenerate in great pulses tied to the rhythm of El Niño — a rhythm that climate change may now be disrupting. See seed banking.
The seeds have almost no dormancy and must germinate at once in the shaded forest floor, and — unusually for tropical trees — dipterocarps depend heavily on ectomycorrhizal fungi (the fungal partners more typical of temperate oaks and pines), which is one reason clearing the forest and its soil fungi makes them so hard to re-establish. See mycorrhizal fungi.
The timber of the tropics
The dipterocarps are also, overwhelmingly, the commercial timber of Southeast Asia, and their trade names are familiar to any builder even if the family is not: meranti, lauan ("Philippine mahogany"), keruing, balau, seraya, and merbau are all dipterocarps.
Their wood is the basis of a huge industry — the tropical hardwood plywood, veneer, and general-construction timber of much of the world comes from dipterocarps — and they also yield valuable resins (dammar, used in varnishes and incense) and oils. That commercial value has driven catastrophic logging and deforestation across the region: the lowland dipterocarp forests of Borneo and Sumatra are among the most heavily logged and cleared forests on the planet, felled for timber and then often converted to oil palm, with the loss of the orangutan's and countless other species' habitat. Because the trees are slow, mast-dependent, fungus-dependent, and poor at regenerating on cleared ground, these forests are extremely hard to restore once lost — making the dipterocarps a central concern of tropical forest conservation and restoration economics. See structural diversity and keystone species.
Growing them
Dipterocarps are trees of the hot, wet, lowland tropics, deeply frost-tender, and mostly enormous, slow, and specialised — not garden or plantation trees in any ordinary sense, though some are grown in enrichment planting, restoration, and research.
The great difficulty in growing them is the seed: it has no dormancy and dies within days or weeks of falling, so it cannot be stored or shipped in the normal way and must be sown immediately and fresh — a serious obstacle to seed banking and to restoring dipterocarp forest, and an active area of research. Establishing them also usually requires their mycorrhizal fungi in the soil. Restoring a logged dipterocarp forest is therefore slow, skilled, and costly work — one more reason the standing forest is worth protecting in the first place. See reforestation techniques.
See also
- Maples the temperate trees with the same spinning winged seeds
- Beech mast flowering as predator satiation
- Oil Palm the crop that so often replaces cleared dipterocarp forest
- Teak another great — but plantation-grown — tropical timber
- Mycorrhizal Fungi the fungal partners dipterocarps depend on
- Reforestation Techniques the difficulty of restoring these forests
- Sal Tree