How microclimate influences the spring phenological responses to decreased snow cover in four tree species seedlings in a boreal forest

Heat accumulation and spring freeze, both strongly influenced by snow cover, are key factors regulating the onset of spring phenology. In forest ecosystems, decreased snow cover due to climate change may differently impact heat accumulation and the occurrence of spring freezes between canopy gap and under the tree canopy, leading to varied phenological responses. In this study, we examined how spring phenology of tree seedling responds to decreased snow cover across microsites and explored whether these responses are species-specific. We conducted a manipulation experiment in a planted forest in northern Hokkaido, Japan, establishing five canopy gap and five under canopy areas, each with control and snow removal plot. Four dominant tree species were planted in each plot. Snow removal significantly advanced budburst and leaf-out in both microsites, with a more pronounced effect observed in the canopy gap. Moreover, snow removal significantly advanced the budburst and leaf-out of all four species in the canopy gap, whereas only Abies sachalinensis showed significantly earlier budburst and leaf-out in the under canopy. Overall, our study demonstrated that projected winter warming led to a greater advancement of spring phenology in tree seedlings in canopy gap compared to under the canopy, with species-specific responses.