Alpine plant species advance green-up but delay leaf senescence in response to experimental early snowmelt

Global warming is causing the snow to melt earlier than usual, while effects on alpine plant communities remain unclear in magnitude and direction, especially in Himalaya. We simulated early snowmelt (ES) conditions at different elevations over 3 years at an alpine site in Western Himalaya to study how ES affects the sequential phenological events of Himalayan alpine plant species. Experimental ES caused (1) advances in early-season phenological events (leaf unfolding, first flowering) and delays in late-season events (end of flowering, leaf senescence); (2) larger shifts in late-season events; and (3) lengthening of the entire flowering and senescence duration. The magnitudes of change and phenotypic plasticity for all phenological events were species-specific and larger for upper elevation species compared to lower elevation species. Hence, the extended growing season of Himalayan alpine plants is governed more by delayed autumn leaf senescence than advanced early spring green-up. The prolonged phenological phases under ES have adaptive advantages, but their energetic efficiency remains uncertain, suggesting further research to clarify how altered phenological phases translate into fitness outcomes under changing alpine conditions.