First study of leaf fossils from Borneo’s rainforest reveals current ecosystem to be ancient

According to an international research team led by Penn State in partnership with Universiti Brunei Darussalam. The results, published in the journal PeerJsuggest that the current landscape is similar to what was present during the Pliocene epoch, 5.3 to 2.6 million years ago, and may provide further justification for the conservation of these forests which are home to many critically endangered species.

“This is the first demonstration that the dominant life form characteristic of Borneo and the whole of the Asian humid tropics, the dipterocarps, were not only present but in fact dominant. We found many more fossils of dipterocarps than any other plant group,” said Peter Wilf. , professor of geosciences at Penn State College Earth and Mineral Sciences and co-funded faculty member of the Institutes of Energy and the Environment (IEE).

Dipterocarps are the tallest tropical trees in the world, and the tallest of them can reach 100 meters (328 feet) in height, or about the height of a 22-story building.

Wilf said dipterocarps include hundreds of keystone species that support tropical Asia’s critically endangered biodiversity by structuring rainforests and providing huge food resources through pollination and their nutritious seeds. Borneo has nearly 270 species of dipterocarps, more than half of the global total.

“Fossil leaves in the humid tropics are very rare due to the extensive forest cover and deeply weathered soils that obscure the rocky exposures,” Wilf said.

Previous studies of the island’s plant life have typically involved fossil pollen, which is highly resistant to decay. However, because dipterocarp pollen often does not store well, these data do not provide complete information about ancient plant landscapes in the Asian tropics, according to Wilf. This study provided extensive fossil evidence from both leaves and pollen, at two sites the team discovered after intensive reconnaissance in Brunei, which supports the idea that the diverse and well-structured vegetation of the current landscape is similar to what was present in the Pliocene epoch, 5.3 to 2.6 million years ago.

“From the same rocks that dipterocarp leaf fossils come from in large numbers, there is hardly any dipterocarp pollen,” he said. “Pollen and spores represent many other plant groups, including many ferns, but virtually no dipterocarps. So this validates the idea that there is a bias against dipterocarp pollen.”

Ferry Slik, a professor at Universiti Brunei Darussalam who studies the ecology of rainforests and co-authored the paper, said it was a hugely important study of the country’s fossil flora.

“There are very few fossil studies from the Asian tropics,” Slik said. “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.”

Wilf and his team unearthed a wide variety of fossil leaves and fruits, including many plant groups that are native today but had never before been found as fossils in the Malay Archipelago. These included three different genera of dipterocarps, such as Dryobalanops, whose species are almost all threatened; understory plants such as jujube Ziziph and melastomas; and a climbing aroid plant, Rhaphidophorawhich is related to the popular houseplant Monstere.

Slik said the team rebuilt an ancient ecosystem almost exactly like what is found in Brunei today.

“With the pollen included, we get a fairly complete representation of mangrove and swamp environments, fringed by lowland tropical rainforests of dipterocarps with very diverse fern understory and many climbers, including more ferns, of jujubes and aroids. So we’re actually getting to see what the environment was like millions of years ago,” Wilf said. “It looked a lot like what you can find out there now, although those habitats have been cut down in much of tropical Asia.”

Wilf said one of the motivations for doing this study was to encourage the conservation of these areas.

“The tropical rainforests are where the biodiversity is. Brunei is about the size of Delaware, but it has more than seven times the plant diversity of all of Pennsylvania,” he said. “This region has an always humid climate similar to that of the Amazon or Central African rainforests. It is home to spectacular animal life such as proboscis monkeys, crocodiles, rhinoceros hornbills, clouded leopards, Sun bears, flying lizards, bearded pigs and slow lorises.”

Although Borneo is one of the great biodiversity hotspots on Earth and its rainforests are ancient, its biodiversity is declining due to logging, agricultural conversion and climate change.

Dipterocarps are highly sought after by the logging industry and Borneo suffers from high deforestation rates, said Slik, who works to improve Asia’s tropical ecosystems.

“Borneo, and much of Asia’s rainforests, are ground zero for the biodiversity crisis,” Wilf said. “However, Brunei is a gem in the system as it is one of the very few countries in the region that still retains more than half of its ancient rainforests.”

According to Wilf, each paleontological discovery highlights the importance of history and provides fundamental support for the establishment of conservation areas and public education.

“If a living group has a known paleo history, it has added preservation and educational value, and it is less likely to be destroyed,” he said. “Paleontology provides the primary evidence of how and why life on Earth is distributed as it is and when different groups of plants and animals arrived.”

This project began as a 2015 IEE Seed Grant for Wilf’s project titled “Palaeobotanical and Genomic Biogeography of Gondwana Living Fossil Trees in Southeast Asian Rainforests: Informing Watershed Biodiversity and Conservation in the face of climate change and deforestation”. Later, funding came from the National Science Foundation and Universiti Brunei Darussalam.

In addition to Wilf and Slik, authors include Penn State graduate Xiaoyu Zou, who completed his dissertation on Brunei’s fossil leaves in tandem with this paper, and former doctoral student Michael Donovan, who now works at the Cleveland Museum of NaturalHistory. Other authors include László Kocsis, University of Lausanne; Antonino Briguglio, University of the Studi di Genova; David Shaw, Biostratigraphic Associates (UK) Ltd; and Joseph Lambiase, Lambiase Geoscience.