Leaf Fossil Study Reveals Borneo's Rainforest Trees 4 Million Years Old

Scientists have recently discovered that dipterocarps, the dominant tree group in the rainforests of Borneo, have been present on the island for at least four million years. A research team led by Penn State University studied the fossilised leaves of the tree and found that the current landscape in the Southeast Asian island is similar to what was present during the Pliocene Epoch - 5.3 to 2.6 million years ago.

“This is the first demonstration that the characteristic dominant life form of Borneo and the entire Asian wet tropics, the dipterocarp trees, was not only present but actually dominant,” said Peter Wilf, professor of geosciences at the Penn State College Earth and Mineral Sciences, adding, “We found many more fossils of dipterocarps than any other plant group.”

The team noted that Borneo island is home to almost 270 dipterocarp species, which is more than half the total global species. They also informed that dipterocarps are among the tallest tropical trees in the world, with some individuals able to grow up to heights of around 100 metres. 

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However, Mr Wilf said that rock fossils of dipterocarp leaves are difficult to come across because of the cover provided by the forest and their soils. He said that previously, fossilised pollen has been used to study plant life on Borneo, but because dipterocarp pollen decays so quickly, there has been a suspicion that these pollen studies haven't shown the whole picture. The team found rocks with many dipterocarp leaf fossils but little in the way of dipterocarp pollen, backing up the bias hypothesis. 

Now, the new study combines both leaf and fossil pollen, identifying the ancient world of mangroves and swamps bordered by tropical lowland rainforests, featuring diverse fern undergrowth and an abundance of climbing plants. Mr Wilf said that the team got to actually see what the environment was like millions of years ago. 

The researchers believe the latest findings add further justification to preserve such prehistoric forests and the many critically endangered species that use them as a home. They said that with tropical Asian biodiversity currently under severe threat, the island plays a crucial role in supporting that biodiversity. 

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As per the researchers, currently, around 89% of the 460 Asian dipterocarp species have “near threatened” status, while 57% are labelled as “endangered, critically endangered or extinct”. The team stated that if we allow the slide to continue, this latest study shows, then we are losing four million years of forest history.