- A new species of stone oak has been described from the forests of northern Sumatra, the first of its kind found on the island in more than 10 years.
- The two lone trees are located in the remote Batang Toru forest, the only known habitat of the critically endangered Tapanuli orangutan, which was itself only described in 2017.
- The new stone oak’s acorns seem to be an important part of the orangutans’ diet, but ongoing habitat destruction means this tree is also likely to be critically endangered.
- Urgent conservation action is needed to save the remaining Batang Toru forest and establish cultivated populations of the rare oak to prevent its extinction, researchers say.
A new species of stone oak tree has been described from deep in the forests of northern Sumatra and appears to be an important source of food for the Tapanuli orangutan, the world’s most threatened great ape.
Named Lithocarpus tapanuliensis, the tree species is the first new stone oak identified on the island in more than a decade, and was described from two lone specimens found by researchers in the remote Pilar Forest, part of the highly biodiverse Batang Toru ecosystem.
This specialized habitat is home to an abundance of rare plants and animals, including the Tapanuli orangutan (Pongo tapanuliensis), a critically endangered species that was itself only described scientifically in 2017.
During a vegetation survey in February 2023, Try Surya Harapan, an Indonesian Ph.D. student at Xishuangbanna Tropical Botanical Garden in China, noticed clues that the new oak species may provide a vital resource for the Tapanuli orangutans.
“I was walking in the forest and noticed an orangutan’s nest,” said Try, who describes the nest as a “thick comfy bed with many leaves and branches.” Not far from the nest, he found fruit remains on the forest floor. “Some fruits were completely eaten and others were just partially eaten. The bite marks seemed from rodents and primates. I was very excited looking at these fruits when I noticed some ‘weird’-looking acorns … From that day, I suspected the acorns belonged to a new locality or even to a yet-to-be-described species.”
Orangutans rely on stone oaks and related species for food and nesting materials. The consistent yearly fruiting of these oaks makes them a vital fallback food source when other resources are scarce.
The stone oaks (Lithocarpus) are endemic to Asia and restricted to the tropics and subtropics. Although closely related to the trees referred to as oaks (in the genus Quercus) they are an evolutionary distinct group with nearly as many species.
The unique cup-like growths surrounding the acorns of L. tapanuliensis distinguish them from other regional stone oak varieties. The acorns also secrete a distinctive resin when dried.
Despite extensive surveying, only the two individual trees have been located so far.
“The species has been assessed as critically endangered due to its tiny population and range size,” Try said. “The Batang Toru ecosystem suffers from habitat fragmentation and habitat loss due to large-scale infrastructure projects, such as mining, agroforestry plantations, and hydropower in the surrounding forest.” Recent development projects have further disrupted the area.
Compared to neighboring islands, Sumatra’s plant diversity remains poorly documented and is assumed to be not as rich as Borneo’s, home to another species of orangutan. But Try said he believes many unknown species like L. tapanuliensis are yet to be uncovered through dedicated exploration across Sumatra’s forests.
“This discovery highlights how Indonesia’s rainforests likely harbor far more biodiversity than currently known. Finding this rare oak tree shows we must survey threatened habitats before they are permanently lost,” he said.
To protect this new species, and the orangutans, we need to save the remaining forest in Batang Toru, he added. He also recommended growing some of these rare trees outside the forest, in places like botanical gardens. Using both methods together gives the species a better chance at long-term survival.
Of the nearly 700 tree species in the Fagaceae family in Asia, around two-thirds should be considered threatened with extinction, according to recent work by the IUCN Global Tree Assessment and Global Tree Specialist Group “Of these, about 590 are Stone Oaks (Lithocarpus) and Chinquapin (Castanopsis),” Joeri Sergej Strijk of the
Alliance for Conservation Tree Genomics told Mongabay in an email.
Without urgent action, extinction of the newly found stone oak, and many other species looms. “We must act quickly to conserve this oak tree and its habitat,” said Try. “Protecting rare species like L. tapanuliensis means protecting Sumatra’s irreplaceable native biodiversity.”
Banner image of an adult female, Pongo tapanuliensis by Tim Laman Batang Toru Forest Sumatran Orangutan Conservation Project North Sumatran Province (CC BY 4.0).
Liz Kimbrough is a staff writer for Mongabay and holds a Ph.D. in ecology and evolutionary biology from Tulane University, where she studied the microbiomes of trees. View more of her reporting here.
Harapan, T. S., Tan, W. H., Febriamansyah, T. A., Nurainas, Syamsuardi, & Strijk, J. S. (2023). Lithocarpus tapanuliensis (Fagaceae), a new stone oak from northern Sumatra and its role as an important resource for critically endangered orangutans. PhytoKeys, 234, 167-179. doi:10.3897/phytokeys.234.106015
FEEDBACK: Use this form to send a message directly to the author of this post. If you want to post a public comment, you can do that at the bottom of the page.