Dipterocarpus tree

Dipterocarps are tall, plain-barked trees that dominate the upper canopy of many tropical and
monsoon forests in Asia. They are massive flowering evergreen trees that belong to the same order
of plants as cotton, chocolate and hibiscus. They reach a height o f 230 feet and are supported by
huge buttresses. A few species are found in Africa and the Indian subcontinent, and one was
recently discovered in South America ,but the fast majority are in Southeast Asia, particularly the
seasonal lowlands of Indonesia's islands. On Borneo they make up half of all the giant canopy trees.
[Source: Emily Harwell, Natural History, July, 1999]
There are hundreds of species of dipterocarp. They represent 13 of the world's 16 genera. All of
them flower over the same two month period Four months later their fruit matures and drops to the
floor and immediately begins to germinate. Almost all non-carnivorous animals in the rain forest---
including orangutans, hornbills, flying foxes, gibbons, rats squirrels, tree shrews---feed on them.
Some species such as orangutans migrate in search of fruiting forests and are more likely to mate
and produce offspring when the forests fruit.
Dipterocarp trees fruit infrequently and crowd out other trees, resulting in forest with sparser and less
reliable food sources than other forests, such as those in the Amazon. Animals that live there have
to work harder and travel further to get food.
Dipterocarp do not need the wind or animals to disperse their seeds. The pea- to walnut-size fruits
have wing-like epals that helicopter down close to the source tree. Mature tress may go three to 10
years without reproducing and then suddenly fill the forest floor with seeds.
Dipterocarp saplings have chemical defenses against pathogens and produce sugar secretion that
attracts certain species of ant that defend the saplings from leaf-eating insects. The saplings grow
tall very fast, sometimes with the help of nutrient-supplying roots
Dipterocarp Fruiting
Dipterocarp trees fruit unpredictably. In the late 1990s, the dipterocarp trees in Southeast Asian rain
forests went through a particularly long period without fruiting. Animals suffered and starved. Then in
1997, after a temporary drop on nighttime temperatures, the cue the trees had been waiting for,
dipterocarp trees throughout Southeast Asia blossoms and fruited.
One of the main reasons why the trees fruit so abundantly and infrequently is that there is no way
the animals of the rain forest can consume all the fruit and seeds if they all appear at the same time
and therefore some seeds with survive and germinate. If one species get out of sync with the mass,
their fruit will immediately be gobbled up and there is less likelyhood that the seeds will survive and
produce saplings. Even other species such as legumes and unrelated trees fruit at the same time as
dipterocarps so their seeds are likely to survive too.
What triggers the fruiting? In Borneo, every five years or so, a series of weather events brings cool
air form Thailand's Khorat Plateau to Borneo. The cooler temperatures cause the trees to bud, flower
and produce fruit. Some scientists believe that genes activated by the cool temperatures cause the
buds to begin forming. The flowers are pollinated by thrips, small fly-like insects that are among the
world's smallest pollinators.
The temperature triggering mechanism probably developed when the dipterocarp trees covered
India hundreds of thousands of years ago and were a response to the cooler temperatures that
occur in the winter months. In Southeast Asia, there are no real seasons. Therefore they are
triggered by infrequent temperature changes.


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