The Tapanuli orangutans (Pongo tapanuliensis) are considered the rarest of the great apes. With a status of “critically endangered,” they have a declining population of no more than 800 individuals and are confined to a single region, in the Batang Toru mountains, in North Sumatra Province, Indonesia.
The debate about the future of this region, and of the Tapanuli orangutans themselves, has focused on threat factors such as large projects like hydroelectric plants, gold mining, and geothermal energy, and their impacts on this habitat and this species.
However, a group of scientists, in an article they published in the journal Biological Conservation, warns that the reality is more complex than one might initially think.
Through satellite data, interviews with local communities, and computer simulations to understand the impacts of these human activities in Batang Toru, the team assessed forest loss since the beginning of the century and the social and economic processes behind it.
The major conclusion of this work is that the Tapanuli orangutans are not being threatened by one factor or another, but by a multiplicity of factors acting together, from extractive industries to logging and agricultural expansion, passing through the increasingly severe impacts of climate change.
According to the study, between 2000 and 2023, Batang Toru lost 7,659 hectares of forest, or 5% of its total forest cover. Deforestation intensified significantly after 2012, coinciding with the start of three large extractive projects in the region.
Based on the digital simulations they created, the researchers estimate that Batang Toru lost a further 3,472 hectares of forest than would have been lost in the absence of these projects.
However, it notes that about 70% of the forest loss recorded since 2000 is associated with small-scale agriculture and logging. Therefore, they argue, while extractive industries have caused a sharp increase in deforestation, agricultural expansion and timber extraction have placed a continuous pressure on the Tapanuli orangutan habitat, a pressure that even intensified during the study period.
Hidden Factors
Satellite imagery and computer simulations do not allow us to fully capture the complexity of reality, the authors say, so interviews with local communities made it possible to uncover social and economic factors that drove deforestation.
According to explanations advanced by the scientists on The Conversation site, changes in the prices of forest products, changes in land ownership, road development, and local livelihoods are all highly relevant factors.
For example, they point out that a drop in rubber prices led some residents to clear these plantations to establish banana crops. “These unregulated land conversions may occur due to overlapping claims on customary lands and state lands, as well as weak oversight of small-scale forest exploitation activities,” the researchers write.
The team thus highlights the importance of combining ecological perspectives with social perspectives in order to have the clearest and most complete possible picture of what is happening. Especially in a region where humans and orangutans have lived side by side for many generations. Only in this way, they suggest, can the major problems be identified and acted upon.
In addition to all that, climate change is also exerting a strong pressure on the Tapanuli orangutans.
An earlier study revealed that the torrential rains that affected Indonesia in 2025 destroyed about 8,300 hectares of forest in the western Batang Toru region. And it is estimated that this resulted in the death of approximately 58 orangutans, about 7% of the species’ global population.
Because the Tapanuli orangutans are threatened by a combination of extractive industries, agricultural expansion, logging, failures in law enforcement and supervision, market forces and climate change, the researchers say that focusing on just one factor or another will not help safeguard the species’ future.
Therefore, they believe that an integrated approach is needed to help protect the landscape on which both orangutans and humans depend.
