Dynamics of flowering phenology of alpine plant communities in response to temperature and snowmelt time: Analysis of a nine-year phenological record collected by citizen volunteers

Phenological modification is one of the most serious effects of global warming on ecosystems with clear seasonality, such as alpine ecosystems in mid- to high latitudes. Changes in flowering time and duration in plant communities are likely to influence plant-pollinator interactions. However, the effects of global warming on community-scale phenology have scarcely been studied in alpine ecosystems. I analyzed the flowering records of fellfield and snowbed communities collected over a nine-year period in the Taisetau Mountains of northern Japan. The flowering structure of alpine communities is composed of a flowering sequence of early-blooming fellfield species (FE), late-blooming fellfield species (FL), and snowbed species. Flowering initiation in FE showed small interannual variation, while peak flowering time was accelerated according to warmer temperature. Both the initiation and peak flowering time of FL depended on heat sum during early summer. The flowering period of fellfield communities was shortened under warmer conditions, and 1 degrees C warming thought to shorten the major flowering period by 3.8 days. The flowering initiation of snowbed plants strongly depended on snowmelt time, and the peak flowering time further advanced in warmer summers. However, the major flowering period of snowbed communities was independent of snowmelt time and thermal conditions because many snowbed species shifted flowering onset days with little changes in flowering period. As a result, the total flowering period of alpine plant communities was largely determined by snowmelt time, independent of thermal conditions. It is predicted that a 10-day earlier snowmelt will shorten the total flowering season by 4.8 days and a 10-day later snowmelt will extend the total flowering season by 5.8 days. Therefore, snowmelt regime is a major determinant factor of the flowering structure of alpine ecosystems. Clarification of snowmelt dynamics is crucial to predict the global warming impacts on the phenology of alpine ecosystems.