Vegetation on the move: elevational shifts and greening dynamics across the Himalayan alpine zone

This study investigates alpine ‘vegetation line' (the upper limit of continuous plant community) dynamics in the Himalayan alpine zone (HAZ) over a 24‐year timescale (1999–2022) using maximum NDVI products derived from Landsat series datasets, adjusted for sampling bias using phenological modelling. Vegetation line elevations across six regions spanning from Ladakh in the west to Bhutan in the east were analysed for temporal dynamics, spatial patterns of elevation and greening/browning trends (i.e. temporal increase or decrease in NDVI). Results revealed consistent upward shifts in vegetation lines across all regions, with rates ranging from 1.42 m year –1 in Khumbu (Nepal) to 6.95 m year –1 in Manthang (central High Mountain Asia). Initial levels of vegetation greenness generally increased from west to east. Across all study regions, greening trends were more prevalent than browning trends, while significant browning trends were observed in more easterly regions, specifically in Khumbu and Bhutan. Integration with the ERA5 dataset suggests snow depth as a key driver associated with the upward migration of vegetation lines, while variations in precipitation appear linked to the extent and intensity of browning. This study is the first to demonstrate vegetation line shifting patterns across the Himalayas at a 30 m spatial resolution, providing robust evidence of upward vegetation line movement under climate change and exploring underlying climatic trends.