The south-east Asian rainforest

February 27, 2012

The south-east Asian rainforest is the oldest, consistent rainforest on Earth, dating back to the Pleistocene period some 70 million years ago, giving it a rich biological diversity that is common to all three tropical forest eco-regions. The south-east Asian rainforest is one of the three main tropical forest eco-regions in the world – the other two being the Congo Basin and the Amazon basin. Sadly, south-east Asia is losing its rainforests faster than any equatorial region, and has the fewest remaining primary rainforests.

Rail transport for SE Asian forestry
Transport in the peat swamp forest is by rail only.
Manual log skidding in SE Asia Oil palm plantations in SE Asia
Logs skidded manually to small train siding. Oil palm plantations.


South-east Asia is a 5 000 km long chain of about 20 000 islands strung between Asia and Australia. In ancient times, as the rest of the world went through cooling and warming periods, the climate of the south-east Asian region remained more stable due to being on the equator and surrounded by water. Because the climate on the equator doesn't change much and the surrounding oceans provide plenty of moisture in the form of rain, the region was able to have consistent forests over very long periods of time. As sea levels rose and fell through warming and cooling cycles, small pockets of forests survived as 'forest refugia', or reservoirs of wildlife from which various species could re-establish themselves. Malaysia and the islands of Borneo, Sumatra and Java were all part of the same landmass during the last ice age. When the glaciers melted and sea levels rose, many of these reservoirs were cut off from each other. This forced species to develop along their own distinctive evolutionary paths in response to local environments, leading to an amazing diversity of species.

One interesting feature of the lowland rainforests of Malaysia, Borneo and Sumatra is the dominance of one family of trees, the Dipterocarpaceae. Dipterocarp are emergent trees and can reach heights of 40 m. Their crowns are supported on large straight trunks. Many epiphytes, like orchids and ferns, grow on the trees and lianas, while vines and strangler figs cling to the trees as they grow towards the sunlight. One of the emergent species is the tualang (Koompassia excelsa) which can reach heights of 90 m. It is the third tallest tree species in the world, and is almost never cut down because of its hard wood and massive buttresses. But most importantly, it is home to honey bees, whose honeycombs hang like enormous wedges from the underside of its branches. These trees are worth more money when left standing. Each of the hundreds of fig species has its own species of pollinating wasp, without which they would become extinct and vice versa. Links within the tropical rainforest ecosystem extend to thousands of plants which support mammals and birds.

Trees don't flower and come into fruit at the same time in the south-east Asian rainforest. Some trees only bear fruit once every three years, some only every decade. The short nutrient cycle makes it difficult for trees to produce large amounts of fruit at regular intervals. Many trees complete the flowering cycle in only one day, and are only receptive for a few hours during the day or night. Very few trees depend on the wind for pollination since there is little movement of air under the dense canopy. These trees depend mostly on animals and insects to pollinate and disperse their seeds.

Political instability in the Indonesian archipelago has resulted in little law enforcement within protected wildlife areas. For example, in 1992, local people took control of the land and began indiscriminate logging and farming in the dipterocarp rainforests. Little regard has been given for the long-term environmental effects, and at the present rate of destruction, there will be very little primary lowland rainforests remaining in this region within the next decade. Illegal logging continues to affect thousands of plant and animal species and upsets the natural biologic equilibrium that keeps a rainforest healthy and stable.

Sumatra has lost 48% of its natural forest cover since 1985, with many of the remaining species endangered. The critically endangered two-horned Sumatran rhinoceros survives in small forest pockets of Sumatra and Borneo. Their entire population is thought to be only 300 to 500 individuals. The Javan rhinoceros has already slipped into extinction. The Sumatran tiger, like its cousin the Javan tiger, is also threatened with extinction. The Asian elephant is another large forest herbivore which needs large amounts of forest to survive. Human encroachment and logging are shrinking their habitat to the extent that they can no longer support the elephants. The Malayan tapir is the largest of the four species of tapir still alive and no more than 50 animals still live in the wild. Another animal found only in Sumatra and Borneo is the orangutan, or 'man of the forest'. They were once found on mainland Asia from Thailand to southern China.

They feed mostly on fruit and move through the forest following the fruiting trees. There are 13 separate species of primates in Borneo's lowland forests alone. Most have overlapping home ranges but have different diets and foraging methods.

Some of the peat swamp forests are managed responsibly by concession owners. In such cases, partial cutting is applied to ensure the sustainability of forest resources. In some cases, logs are removed through the construction of temporary railway lines within the swamp forest. The systematic way of moving through the area is based on the construction and subsequent dismantling of these railway lines, which leads to work areas being concentrated in a cutting block allocated for 10-year planning periods. Once the rail has been dismantled, access largely ceases and it becomes uneconomic to return until full regeneration has taken place.

During partial cutting operations, logs are felled and bucked at the felling site then manually skidded to a log landing at a temporary railhead. The logs are then manually rolled on to the railway carriages. The flat terrain allows for the rail system to be laid out on a regular grid with temporary tracks being run into each year's harvest area.

Published in December 2011

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