Disentangling the impacts of agriculture, logging, and extractive industries on Tapanuli orangutan habitat: A geo-ethnographic assessment

Rapid land-use change across Southeast Asia has placed many narrowly distributed endemic species at imminent risk of extinction. In the Batang Toru Key Biodiversity Area (North Sumatra, Indonesia), small-scale logging, agriculture expansion, and three major mineral and energy projects (gold mining, geothermal energy, and hydropower dam; hereafter extractive projects) threaten the last remaining habitat of the critically endangered Tapanuli orangutan ( Pongo tapanuliensis ). We combined geospatial mapping, causal inference, and ethnography to estimate the effects of these activities on forest loss within unprotected areas of Batang Toru. Using a synthetic control approach, we estimated a counterfactual trajectory that reflects potential forest loss in the absence of extractive projects initiated in 2012. We also applied segmented regression to identify temporal shifts in forest loss drivers between 2000 and 2023. Batang Toru lost 7659 ha (~5%) of forest during this period, with annual loss rates doubling after 2012. The area lost 3472 ha more forest than expected under the counterfactual scenario, suggesting added impacts from extractive projects. However, post-2012 forest loss remained dominated by smallholder agriculture and small-scale logging, together accounting for ~70% of total loss. Ethnographic data confirmed that these activities continue to drive forest loss independently of extractive projects. Effective conservation in Batang Toru will therefore require not only regulating major extractive projects but also: 1) clarifying and securing land tenure, 2) integrating incentive-based approaches that align local livelihoods with biodiversity protection, and 3) strengthening monitoring and accountability of small-scale logging.