Waning snowfields have transformed into hotspots of greening within the alpine zone

Declining seasonal snow cover duration leads to changing conditions for plant recruitment and growth in temperate mountains. Yet capturing the intricacy of snow cover and vegetation dynamics at multidecadal scale in complex terrains poses a great challenge. Here we show that over the last four decades the greenness trend in European mountains increases with the annual date of the seasonal snow cover disappearance. By combining satellite data of high spatial resolution and downscaled climate re-analysis we show that the reduction in snow cover duration surpasses elevated temperatures in influencing heat accumulation during the growing season. This accumulation is a key driver of the pronounced greening observed in late snow-melting sites, particularly in sparsely vegetated, north-facing screes. Our results provide a comprehensive account of rapid vegetation changes in waning snowfields and highlight the pivotal role played by snow cover dynamics to unravel the complexity of greening within the temperate alpine zone.