Humans Have Influenced Southeast Asian Rainforests Since Last Ice Age

A study of rainforest vegetation on mainland Southeast Asia and three heavily forested island there has revealed that humans have been shaping the forests for the last 11,000 years.

The find runs contrary to the standing belief that the rainforests of Thailand and Vietnam as well as those on the islands of Borneo, Sumatra and Java have been largely unaffected by humans.

Writing in the Journal of Archeological Science, a research team led by Chris Hunt, a paleoecologist at Queen's University Belfast, reports that these Southeast Asian rainforests show a pattern of repeated disturbances by humans dating back to the last Ice Ace, about 11,000 years ago.

Finding physical evidence of human disturbances in dense rainforest is exceedingly difficult using traditional archaeological methods, the researchers said.

Instead, Hunt and his colleagues, including Ryan Rabett from Cambridge University, turned to pollen samples and a reassessment of existing paleoecological research.

"It has long been believed that the rainforests of the Far East were virgin wildernesses, where human impact has been minimal. Our findings, however, indicate a history of disturbances to vegetation. While it could be tempting to blame these disturbances on climate change, that is not the case as they do not coincide with any known periods of climate change. Rather, these vegetation changes have been brought about by the actions of people," Hunt said in a statement.

"There is evidence that humans in the Kelabit Highlands of Borneo burned fires to clear the land for planting food-bearing plants. Pollen samples from around 6,500 years ago contain abundant charcoal, indicating the occurrence of fire," Hunt continued. "However, while naturally occurring or accidental fires would usually be followed by specific weeds and trees that flourish in charred ground, we found evidence that this particular fire was followed by the growth of fruit trees. This indicates that the people who inhabited the land intentionally cleared it of forest vegetation and planted sources of food in its place."

Hunt went on to say that one of the major factors of human activity shaping rainforest is the "sheer prevalence" of weed trees such as Macaranga, Celtis and Trema. Recent studies have shown that these quick-growing weed trees are coming following episodes of burning or other forest disturbances in the region.

Hunt also reports that people imported Sago tree seeds to Borneo when they traveled there from New Guinea.

"Nearer to the Borneo coastline, the New Guinea Sago Palm first appeared over 10,000 years ago. This would have involved a voyage of more than 2,200km from its native New Guinea, and its arrival on the island is consistent with other known maritime voyages in the region at that time - evidence that people imported the Sago seeds and planted them," he said.

In the future, the research could be taken into account as logging companies try to clear old-growth forests in Southeast Asia. These companies, Hunt said, have worked to evict indigenous forest-dwelling people on the grounds that they play no role in supporting the forest.

"Laws in several countries in Southeast Asia do not recognize the rights of indigenous forest dwellers on the grounds that they are nomads who leave no permanent mark on the landscape. Given that we can now demonstrate their active management of the forests for more than 11,000 years, these people have a new argument in their case against eviction," Hunt said.