Forest gain in high elevations of the Himalayas revealed by long-term satellite records

The Himalayas host the planet's highest-elevation mountain forests, serving as natural sentinels of climate change. Despite evidence of accelerated shifting alpine treelines, changes in the entire Himalayan forest system remain understudied. In this study, we derive tree cover from long-term Landsat observations using machine learning algorithms and find a significant overall increase in tree cover by 2.5 percentage points from 1990 to 2020. At the scale of the entire Himalayas, the fastest increase occurred at higher elevations (1,000 to 3,500 m above sea level (a.s.l.)) at an annual rate exceeding 0.15% yr−1, whereas within the monsoonal Himalayas, even higher rates occurred between 1,000 and 2,500 m a.s.l. (>0.3% yr−1). We analyze forest change over the three decades in relation to climate and land cover datasets and validate the results with Google Earth Pro imagery. Forest gains in the monsoonal and westerly Himalayas were mainly associated with rising temperatures and changing precipitation patterns, respectively. Forest losses were dominated by the expansion of cropland and built-up areas, especially in the lower elevations. These findings highlight the value of long-term satellite records for detecting elevation-dependent forest changes and supporting sustainable forest management in the Himalayas.