Upward expansion and acceleration of forest clearance in the mountains of Southeast Asia

Southeast Asia contains about half of all tropical mountain forests, which are rich in biodiversity and carbon stocks, yet there is debate as to whether regional mountain forest cover has increased or decreased in recent decades. Here, our analysis of high-resolution satellite datasets reveals increasing mountain forest loss across Southeast Asia. Total mean annual forest loss was 3.22 Mha yr−1 during 2001–2019, with 31% occurring on the mountains. In the 2010s, the frontier of forest loss moved to higher elevations (15.1 ± 3.8 m yr−1 during 2011–2019, P < 0.01) and steeper slopes (0.22 ± 0.05° yr−1 during 2009–2019, P < 0.01) that have high forest carbon density relative to the lowlands. These shifts led to unprecedented annual forest carbon loss of 424 Tg C yr−1, accelerating at a rate of 18 ± 4 Tg C yr−2 (P < 0.01) from 2001 to 2019. Our results underscore the immediate threat of carbon stock losses associated with accelerating forest clearance in Southeast Asian mountains, which jeopardizes international climate agreements and biodiversity conservation. Southeast Asia contains half the world’s tropical mountain forests. This study finds increasing mountain forest loss there, with the clearing frontier moving higher in the 2010s and causing unprecedented carbon loss.