Leaf fossils in Borneo reveal ancient forest 4 million years old

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Leaf fossils from Borneo have been studied in detail for the first time, researchers say, revealing that the rainforests that cover the surface of the island have been in place and have been supporting biodiversity for at least 4 million years.

The current landscape, dominated by dipterocarpslooks a lot like it would have looked in the Pliocene epoch around 2.6 to 5.3 million years ago, the researchers say – and that makes it a valuable ecosystem to preserve for future generations.

Borneo is home to nearly 270 species of dipterocarps, more than half of the total number of species worldwide. As tropical Asian biodiversity is currently under serious threat, the island plays a crucial role in supporting this biodiversity.

A fossil fragment of a huge dipterocarp leaf. (Wilf et al., PeerJ, 2022)

“This is the first demonstration that the dominant life form characteristic of Borneo and the whole of the Asian humid tropics, the dipterocarps, was not only present but in fact dominant,” he added. says paleobotanist Peter Wilf, from Pennsylvania State University. “We found many more dipterocarp fossils than any other plant group.”

These dipterocarps are among the tallest tropical trees in the world, some individuals capable of growing to a height of about 100 meters (328 feet).

However, rock fossils of their leaves are difficult to find, due to the cover provided by forests and their soils, according to to Wilf.

Previously, fossilized pollen has been used to study plant life in Borneo, but because dipterocarp pollen breaks down so quickly, it is suspected that these pollen studies did not show the whole picture. Here, the team found rocks with many dipterocarp leaf fossils but little dipterocarp pollen, supporting the bias hypothesis.

(Peter Wilf et al.)

This new study combines both leaf and fossil pollen, identifying an ancient world of mangroves and swamps bordered by lowland tropical rainforests, with diverse fern undergrowth and an abundance of climbing plants.

“We are starting to see what the environment was like millions of years ago,” said Wilf. “It looked a lot like what you can find there now, although those habitats have been culled across much of tropical Asia.”

Forests are under pressure from logging activities, agricultural land conversion and climate change. There are high rates of deforestation in Borneo, although in the Brunei region of the island – where the study was carried out – the majority of ancient rainforests are still preserved.

Maintaining and expanding this preservation should be a top priority, the researchers say. Through pollination and a vast supply of nutritious seeds, dipterocarps provide the foundation of life for many types of flora and fauna, including proboscis monkeys, clouded leopards, sun bears, and rhinoceros hornbills.

leaffossilvsmeasuringleaf(Peter Wilf et al.)

Now, about 89 percent of the 460 species of Asian dipterocarps have Near Threatened status, while 57 percent are labeled as Endangered, Critically Endangered or Extinct. If we let the slide continue, as this latest study shows, then we lose four million years of forest history. A better understanding of the area’s history should aid conservation efforts.

“There are very few studies of fossils from the Asian tropics,” says environmentalist Ferry Slikfrom the University of Brunei Darussalam.

“I hope this study will further stimulate fossil research efforts in the tropics, as they will tell us a lot about the natural history of the region.”

The research has been published in PeerJ.

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