Early snowmelt accelerates bud break but has mixed effects on leaf area of understory woody plants in a heavily snow-covered deciduous forest in northern Japan

Climate change induces earlier snowmelt in most regions and extends growing seasons for woody plants. However, there is still limited understanding of how the relative impacts and interactions of light, temperature, and water conditions altered by early snowmelt affect phenological and morphological traits of understory plants. We conducted snow removal experiments in a heavily snow-covered forest. We compared bud break dates and leaf size developments with the effects of snow removal in understory Fagus crenata, Lindera umbellata, and Viburnum furcatum. Snow removal increased temperature and light conditions around buds but decreased the soil moisture during bud break. Removing snow one month before ambient snowmelt accelerated bud break but only by 5.9-11.9 days. Bud break in individuals with snow removal required more thawing degree days around buds than under ambient conditions. Leaf areas of V. furcatum in the snow removal were smaller than those in controls. Summarizing changes in light conditions and leaf area growth, the earlier bud break and leaf growth did not result in greater light capture potential over the spring period in L. umbellata and V. furcatum. Although earlier snowmelt accelerates bud break and leaf expansion in these plants, this may not result in greater carbon accumulation.