Mark McGinley's Fulbright in Malaysia: Taman Negara- Rainforest Trees

The rainforest is the definite star of Taman Negara and the central characters in a rainforest are the rainforest trees. Let's try to learn a little more about rainforest trees.

Dipterocarps

Lowland tropical rainforests in many parts of Asia are dominanted by dipterocarps. Dipterocarps are plants that are members of the Family Diptocarpaceae a family containing 17 genera and over 500 species. The name dipterocarp comes from Greek (di = two, pteron = wing and karpos = fruit) and refers to the two-winged fruit produced by these trees.

Dipterocarps dominate forests in Borneo, Sumatra, Java, the Malaysian Peninsula, and wet regions of the Philipines. Generally, dipterocarps are tall trees that produce straight smooth trunks. Some dipterocarps may grow up to 50 meters tall. Normally, dipterocarp trunks do not branch until they reach the canopy.

Because many dipterocarps produce such long trunks, it is important that the base of the tree are capable of supporting the mass of these large trunks. Most trees rely on the root system to help support the trunk.

To understand how dipterocarps support their trunks it is necessary to know something about how nutrients cycle in tropical ecosystems. All plants require nutrients, such as nitrogen and phosphorous, to grow. Plants pick up nutrients from the soil using their roots. Although tropical ecosystems (the soil and the living plants and animals) contain lots of nutrients, the concentration of nutrients in the soil is relatively low because most nutrients are held in the tissues of living organisms (mostly the plants). Moreover, the nutrients are concentrated near the surface. When animals and plants die, their bodies (that contain lots of nutrients) fall to the forest floor. Because the high temperature and moisture level of tropical ecosystems are perfect for the growth of bacteria and fungi that are the main decomposers, the rates of decomposition in the rainforest is very fast. Becuase there are so many plants in these communities, then these nutrients are picked up very quickly, so the nutrients never have time to move deeper into the soil. Thus, the roots of many tropical trees grow near the surface rather than growing deep beneath the surface.

Shallow roots are not as effective as anchoring trees into the soil as deeper roots. Dipterocarps supporte their tall trunks by producing structures known as buttresses. These buttresses are so effective at stabilizing trees that dipterocarps are less likely to be blown over by high winds than tropical trees from the Amazon Basin on the Congo.

Because of the large biodiversity in the tropics there are lots of organisms that want to attack and eat any trees. Dipterocarps protect themselves by producing oily resins and tannins that defend them against infection and herbivores.

Dipterocarps reproduce by producing a large number of small flowers. Seeds are contained in winged-fruits that rotate as the fall to the ground and thus increase the potential distance that these fruits can be dispersed by the winds. Most dipterocarps do not flower every year, but interestingly most of the plants of the same species flower in the same years in a phenomenon known as "mast years".

Some dipterocarp fruits.