Fossil evidence confirms the persistence of prehistoric forests in Brunei

  • A recent study published in the journal PeerJ reports the excavation of fossilized leaves from ancient forests at least 4 million years old in Brunei on the island of Borneo.
  • More than 80% of the leaves the team found belonged to the family Dipterocarpaceae, trees that remain dominant today, confirming their longstanding role in anchoring Borneo’s species-rich ecosystems.
  • The discovery adds urgency to protecting these forests from logging or development for agriculture, because once they are gone, they will be difficult to recover, the authors say.

On a sunny, windless beach in Borneo, one of the biggest challenges paleobotanist Peter Wilf faced in his team’s plant fossil hunt was getting used to a new set of tools. The damp ground they probed for ancient plant detritus had never completely turned to stone, so it crumbled with all but the most delicate touch.

They found they were fine if they could get a slice 30 centimeters (12 inches) across – nothing like the 2-meter (6.5-foot) pieces of rock Wilf used to carve in fossil beds in Argentina. And he had to work with a simple penknife, replacing the gas-powered drill or even the backhoe that is part of a paleontologist’s kit in places like the US state of Wyoming.

“You can almost dig up the fossils by hand,” said JW Ferry Slik, a botanist at the University of Brunei Darussalam and one of Wilf’s collaborators.

It wasn’t easy, but the team dug up fossilized leaves and other plant material from two main sites in Brunei, which is on the west coast of Borneo. The process of drying and carefully packing them, clearing them and shipping them in suitcases from Brunei to the United States was painstaking and took months. But in the end, the evidence uncovered by the researchers revealed that the prehistoric forests on the island at least 4 million years ago looked quite similar to what exists today.

A fossil fragment of a huge dipterocarp leaf (estimated size 160 square centimeters or 25 square inches) is an exemplary specimen and one of the largest fossils in the collection. Image courtesy of Wilf et al. (2022).
Brunei Fossil Leaf.
Evidence uncovered by the researchers revealed that prehistoric forests on the island at least 4 million years ago resembled what exists today. Image courtesy of Wilf et al. (2022).

More than 80% of the leaves they found were from Dipterocarpaceae, a family of giant rainforest trees that anchor modern forests across the island, shared by Brunei, Indonesia and Malaysia.

“This type of forest is ancient, and it worked more or less the same way for a long time,” said Wilf, a geosciences professor at Pennsylvania State University and a faculty member at the Institutes of Energy and Energy. of the university environment. Today, this type of forest continues to anchor ecosystems across the island that are home to countless species.

The team reported their findings on March 24 in the newspaper PeerJ.

“It is a fascinating description of a paleobotanical study that supports long-held hypotheses about the ancient nature of Borneo’s rainforest communities, in their composition and distribution,” Charles Cannon, botanist and director of the Center for Tree Science from Morton’s Arboretum in the United States, Mongabay told in an email. Cannon (no relation to the author of this article), who was not involved in the study, said he would have liked to see the samples identified more thoroughly, but added that he was surprised that the team could even find plant macrofossils” under these conditions.

The study illustrates techniques that could still pull back the curtain on the region’s ancient history, said Robert Morley, a geologist at consultancy Palynova Limited, who was not involved in the research.

A gecko hunting at night in Borneo.
A gecko hunting at night in Brunei. Image by John Cannon/Mongabay.

“The main benefit of this paper is that it shows potential local paleobotanists how fossil leaf beds can be usefully studied using modern methods,” Morley said in an email.

He noted that scientists have long known about the enduring presence of the din in this region. Peter Ashton, professor emeritus in the department of organismal and evolutionary biology at Harvard University, who was not part of the study team, also said that evidence of dipterocarps from plant parts and of pollen date back at least to the middle of the 20th century.

Still, the study provides further evidence of how long these forests last and the biodiversity they support, Cannon said.

Today, Borneo’s mega-diverse forests are under threat. Cannon said this is partly due to natural sea level rise since the world’s glaciers began to melt around 10,000 years ago. As the seas rose, existing forests shrank and broke up. Today, logging and agriculture are also causing massive degradation or evaporation of tracts of Borneo’s venerable forests. As he and his colleagues argue in a 2009 study published in the Proceedings of the National Academy of Scienceswhich created “a double whammy for the overall process of diversification and adaptation,” Cannon said.

Another recent study, published in Conservation Biologyrevealed that much of the land supporting key tree species across Southeast Asia is unprotected.

Now, this new evidence confirming the age and history of these forests makes their conservation even more urgent.

“If this forest disappears, as is currently happening quite quickly, then it will be very difficult to get it back,” Slik said.

A map of Borneo
A map of Borneo from the research publication shows the nation of Brunei where the fossils were excavated. Image courtesy of Wilf et al. (2022).

Relatively small Brunei remains an exception, having set aside forest reserves that cover more than half of the country’s land area. But global demand for products like rubber, palm oil and tropical hardwoods has driven deforestation at a breakneck pace across neighboring Indonesian and Malaysian Borneo.

“There’s kind of an idea that you can cut it and it will grow back,” Wilf said. “But that’s not what we see in Southeast Asia.”

The region’s shrinking forests have also heightened the urgency of cataloging the life they support, as well as understanding how Borneo’s immense biodiversity, rooted in its flowering flora, came to be – an idea that motivated Wilf.

“Even though the fossils are disappearing, we don’t really know enough about the history of these places,” he told Mongabay.

Much of what modern paleobotanists know about ancient plants comes from ancient pollen. Often hard-shelled and microscopic, these capsules of plant genetic information have a knack for surviving in sediment for millennia. Identification by discerning scientists in the laboratory then provides an approximation of the composition of plants that existed at a given location millions of years ago.

In the case of dipterocarps, however, their pollen does not seem to hold up so well through the ages – one reason why the prevalence of dipterocarps in these old growth forests has not been so clear until now.

A tree in an ancient forest in Brunei.
A tree in an ancient forest in Brunei. Image by John Cannon/Mongabay.

Past searches have often failed to detect dipterocarp pollen, Wilf said. This has led to questions about their place in ancient ecosystems, he said: “Were they abundant? Were they important?

At their research sites in Brunei, Slik said, periodic flooding in the distant past would have covered parts of the forest floor with fine clay, essentially preserving the leaf deposits more or less as they were at that time. -the.

“Leaf repositories are considered…almost the closest thing to snapshot repositories,” Wilf said. And in those deposits the team excavated, more than 80% of the leaves belonged to the dipterocarp family, although pollen from trees in the family was harder to find.

“These are keystone species,” Wilf said.

The researchers also found leaves of likely understory vines, as well as fungi, ferns, and an ancient group of plants called lycophytes that include modern lycophytes.

“We’re starting to get this three-dimensional picture of what the forest was like based on what we found,” Wilf said. “It’s an exciting part when you can put it all together.”

Wilf said he hopes evidence of the long history of these forests in Brunei and the island of Borneo will raise wider awareness of their importance – and the consequences if they are allowed to disappear.

“You’re going to lose a unique, highly functioning Earth system that supports wildlife, supports humanity, supports biodiversity, supports carbon sequestration,” he said. “And the human population will be much poorer for it.”

A spider in the forests of Brunei.
A spider in the forests of Brunei. Image by John Cannon/Mongabay.

Banner image: A river running through ancient lowland rainforest in Brunei. Image by John Cannon/Mongabay.

John Cannon is a feature writer with Mongabay. Find him on Twitter: @johnccannon


Cannon, CH, Morley, RJ and Bush, AB (2009). The current tropical refuge forests of Sundaland are not representative of their biogeographical past and are very vulnerable to disturbance. Proceedings of the National Academy of Sciences, 106(27), 11188-11193. doi:10.1073/pnas.0809865106

Gaisberger, H., Fremout, T., Kettle, CJ, Vinceti, B., Kemalasari, D., Kanchanarak, T., … Jalonen, R. (2022). Valuable tree species of tropical and subtropical Asia threatened. Conservation Biology, e13873. doi:10.1111/cobi.13873

Wilf, P., Zou, X., Donovan, MP, Kocsis, L., Briguglio, A., Shaw, D., … Lambiase, JJ (2022). Early fossil leaf floras from Brunei Darussalam show dipterocarp dominance in Pliocene Borneo. PeerJ, ten, e12949. doi:10.7717/peerj.12949

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