Abstract: Duration of snow cover and the timing of snowmelt are important environmental factors determining the diversity of alpine ecosystem. Variation in timing of snowmelt greatly influences not only distribution and phonological schedules of alpine plants, but also pollination efficiency and reproductive success within and among species. For example, neighboring populations situated under different snowmelt conditions may have very different reproductive schedules, resulting in genetic separation through pollination process occurs between them. In addition, quality and quantity of pollinating insects varies throughout the season. Thus, the pollination efficiency of plants should be influenced by the timing of flowering. Such differences in reproductive situations may create and maintain the variation in genetic structure and mating systems of plants within local areas along snowmelt gradients. If global warming modifies the snowmelt regimes in alpine regions, genetic barriers among populations and biological connections between plants and animals should be changed. However, these questions have been poorly studied in alpine ecosystems. I will introduce our studies conducted in the Taisetsu Mountains in northern Japan. Japanese mountains are characterized by the cold and snowy winter and the mild and wet summer, and such seasonally variable ecosystems are expected to be seriously impacted by climate change.