Effects of snowmelt timing on reproductive phenology and pollination process of alpine plants (scientific paper)

Comparative studies on alpine plants along a snowmelt gradient bring us good information about the selective force of short growing season acting on plants. Flowering and fruiting phenologies of each species are potentially determined by temperature, and actual flowering and fruiting times are influenced by the timing of snow disappearance. Snowmelt pattern within an area is rather stable, but actual time of snowmelt at the same place is highly variable from year to year. Early flowering induced by early snowmelt often reduces pollination success because activity of pollinating insects is low in early cool conditions. On the other hand, delay of flowering restricts the length of the fruit developing season, and plants in late snowmelt habitats sometimes fail to set seeds even if pollination is successful. Steep snowmelt gradient causes variations of flowering pattern within and among species and visitation pattern of pollinators. This may accelerate inter-specific competition for pollinator acquisition among plants which affects reproductive success in each species. Thus, the distribution pattern of plants along a snowmelt gradient should be explained not only by abiotic environments (snow depth, snow-free period, soil condition and micro-topog-raphy) and physiological traits of each species (tolerance for short growing season and temperature dependent phenological traits), but also by biotic interactions (plant-plant interaction and plant-insect interaction)