Flowering phenology in alpine grassland strongly responds to shifts in snowmelt but weakly to summer drought

Abstract Alpine plants complete their seasonal phenological cycle during two to three snow-free months. Under climate change, snowmelt advances and the risk of summer droughts increases. Yet, photoperiodism may prevent alpine from benefiting an earlier start growing season. To identify drivers flowering phenology in seven main species grassland, we experimentally shifted date through snow manipulations, excluded precipitation summer. With “time-to-event” models, analysed beginning with respect temperature sums, time after snowmelt, calendar day (photoperiod). We identified types: four tracking dates directly or a certain lag set by including dominant sedge Carex curvula , Anthoxanthum alpinum Helictotrichon versicolor Trifolium photoperiod: Geum montanum Leontodon helveticus Potentilla aurea . Photoperiodism did not act as daylength threshold but rather modulated thermal sums at flowering. Hence, photoperiod delayed snowmelt. The grass A. was only one that clearly responded drought longer remarkably high importance for both types suggests onset warmer climate, particularly non-photoperiod-sensitive species, increasing freezing damages potential disruptions biotic interactions most frequent type grassland across Alps. Consequentially, distinct microclimate species-specific responses challenge temperature-only based projections warming effects on plant species.