Recent floods and landslides in northern Sumatra have once again drawn urgent attention to the precarious future of the Tapanuli orangutan, the world’s rarest great ape, found nowhere else on Earth but the Batang Toru forest.
Extreme rainfall in late 2025, following Cyclone Senyar, and into early 2026 caused widespread damage across the region. Villages were destroyed, forest habitat was fragmented, and further pressure was placed on a species already numbering fewer than 800 individuals. Conservation organisations working on the ground estimate that up to 10% of orangutans may have perished, been displaced, or cut off from critical feeding areas as a result. Satellite imagery has shown nearly 12,000 acres of forest on mountain slopes destroyed by landslides, although the true extent is likely to be even greater, as cloud cover limits visibility.
These events underline a stark reality. Climate driven disasters are now compounding long standing human pressures on the Batang Toru ecosystem.
Development, controversy and the Batang Toru forest
For much of the past decade, the Batang Toru forest has been at the centre of controversy surrounding a large hydropower development, promoted as a key part of Indonesia’s renewable energy strategy. The project, built by POWERCHINA and majority owned by SDIC Power Holdings, has progressed over several years, with completion dates repeatedly delayed.
The scheme has faced sustained opposition from scientists and conservationists due to its location within critical Tapanuli orangutan habitat, alongside concerns about forest fragmentation, landslides and wider ecological impacts.
Following the devastating floods, Indonesia’s government announced the revocation of permits for dozens of companies found to have violated forestry regulations across northern Sumatra. While officials did not publish a formal list, multiple independent reports indicate that the Batang Toru hydropower project is among those affected. As of early 2026, its long term future remains uncertain, pending reviews and possible re audits.
Looking back: monitoring support in 2019
Long before the recent floods, we recognised the importance of independent, long term monitoring in Batang Toru. In 2019, when development pressures were intensifying, we supported the Sumatran Orangutan Conservation Programme (SOCP) via the Ape Alliance, helping to sustain vital research and monitoring work focused specifically on the Tapanuli orangutan.
This work is centred at the Batang Toru Monitoring Station, Camp Mayang, located in the west Batang Toru forest block. Established in 2006, the station is unique. It is the only orangutan monitoring site in an upland forest setting, and the only one dedicated exclusively to Pongo tapanuliensis.
A small team of full time local researchers work to:
- Monitor known, habituated orangutans and track population health
- Record forest phenology to understand food availability and ecosystem change
- Document wider biodiversity, including reptiles, amphibians, figs and orchids
- Contribute to field guides that capture the ecological richness of Batang Toru
SOCP activities have been severely impacted by the recent floods with some of their research stations completely destroyed.
Why this matters now
As climate extremes intensify and land use pressures continue, long term monitoring is no longer a ‘nice to have’. It is essential. Data collected over years allows conservationists to understand how orangutans respond to sudden shocks such as flooding, as well as slower burn threats such as habitat fragmentation and climate change.
The recent floods are a sobering reminder that conservation is not only about protecting species from a single threat, but about safeguarding entire ecosystems against a rapidly changing future. Continued support for on the ground research, local expertise and independent monitoring remains one of the most powerful tools we have to help the Tapanuli orangutan survive.
Image: Andrew Walmsey, Ape Alliance
