The longtime impact of human beings has been found in tropical rainforests previously thought to be pristine.

A study of pollen samples across the three Pacific islands -- Borneo, Sumatra, Java -- and the Southeast Asian mainland, mainly Thailand and Vietnam, has revealed the tropical forests there, believed untouched by humans in the past, have in fact been affected by people for the last 11,000 years or so.

"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," palaeoecologist Chris Hunt from Queen's University Belfast in Northern Ireland said in a release.

"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," he said.

Since more traditional archaeological methods used to locate and excavate sites are hard to use in dense forests, pinpointing evidence of human activity in rainforests is extremely difficult, Hunt explained. But pollen samples and a major review of existing fossil research suggest human activities.

"There is evidence that humans in the Kelabit Highlands of Borneo burned fires to clear the land for planting food-bearing plants," Hunt said. "Pollen samples from around 6,500 years ago contain abundant charcoal, indicating the occurrence of fire."

Fires that burned naturally in the region would have usually been followed by the enhanced growth of certain weeds and trees that tend to flourish in charred ground, Hunt said. However, there were indications many fires over the many years were followed by the appearance of fruit trees, suggesting people intentionally set the fires to clear forest vegetation and plant sources of food instead.

"These vegetation changes," Hunt said, "have been brought about by the actions of people."