Forest microclimates significantly influence how ecosystems respond to global climate change, yet our understanding of their specific impact on ecological processes, such as plant phenological responses, remains limited. Rising air temperatures and shifting precipitation reduce seasonal snow cover depth and duration. This change in snow cover could accelerate or delay spring phenology, resulting in a longer or shorter growing season. Moreover, in canopy gap and under-canopy areas with significantly different microclimates, including air temperature, soil moisture, and light intensity, plant spring phenology would respond differently, as these microclimates can directly affect spring phenology. To investigate these dynamics, we conducted a snow removal experiment in both canopy gaps and under-canopy areas in a boreal forest. Our aim was to elucidate how decreased snow cover and forest microclimates mutually influence tree seedling spring phenology (budburst and leaf-out). In addition, as spring phenology of different species may be influenced by various factors, such that, pioneer species typically constrained by temperature and late successional species likely affected by both temperature and photoperiod, we anticipated that the responses of spring phenology in different species would vary in reaction to the interaction of decreased snow cover and forest microclimate.
　The experiment took place in a planted Picea glehnii forest in Teshio, Hokkaido. To create canopy gap areas, Picea glehnii in five 20m×20m areas were all clear-cut. Control and snow removal plots were established in both canopy gap and under-canopy areas. Acer pictum, Quercus crispula, Abies sachalinensis, Picea glehnii were planted in each plot. Snow removals were conducted twice in December 2022, and in March 2023 aligning with the local past climate and IPCC RCP 4.5 scenario, to shorten the duration of snow cover. Observations of budburst and leaf-out were made twice or thrice a week.
　The results revealed that both budburst and leaf-out in the snow-decreased plots and canopy gap areas occurred earlier compared to the control plots and under-canopy areas. The significant mutual effect of decreased snow and microclimate was detected in leaf-out but, which indicated that canopy gap enlarge the effect of decreased snow caused earlier leaf-out. Examining each species, evergreen conifer species exhibited more sensitive phenological responses to decreased snow, microclimate, and their interaction than deciduous broadleaf species. In this presentation, we also aim to discuss the underlying mechanisms of microclimate, decreased snow, and their interaction causing phenological advancement, and the varied responses observed among different species.