Quantification of leaf area index (LAI) is essential for understanding forest productivity and the atmosphere–vegetation interface, where the majority of gas and energy exchange occurs. LAI is one of the most difficult plant variables to adequately quantify, owing to large spatial and temporal variability, and few studies have examined the horizontal and vertical distribution of LAI in forest ecosystems. In this study, we demonstrated the LAI distribution in each layer from the understory to canopy using multiple-point measurements (121 points) and examined the relationships among layers in a cool-temperate deciduous forest. LAI at each point, and the spatial distribution of LAI in each layer, varied within the forest. The spatial distribution of LAI in the upper layer was more heterogeneous than that of LAI at the scale of the entire forest. Significant negative correlations were observed between the upper- and lower-layer LAI. Our results indicate that the understory compensates for gaps in LAI in the upper layer; thus, the LAI of the entire forest tends to remain spatially homogeneous even in a mature forest ecosystem.

As plant distribution and performance are determined by both environmental and genetic factors, clarifying the contribution of these two factors is a key for understanding plant adaptation and predicting their distribution under ongoing global warming. Betula ermanii is an ideal species for such research because of its wide distribution across diverse environments. Stomatal density and size are crucial traits that plants undergo changes in to adapt to different environments as these traits directly influence plant photosynthesis and transpiration. In this study, we conducted a multi‐location common garden experiment using B. ermanii to (1) clarify the contribution of both environmental and genetic factors to the variation in stomatal density and size of B. ermanii, (2) demonstrate the differences in the plasticity of stomatal density and size among B. ermanii populations, and (3) understand how stomatal density and size of B. ermanii would respond to increased temperature and changing precipitation patterns. Genetic factors played a more significant role in stomatal size than environmental factors, suggesting that B. ermanii struggles to adjust its stomatal size in response to a changing environment. Our results also revealed a positive correlation between stomatal size plasticity and original habitat suitability, indicating that in B. ermanii populations in harsh environments exhibit lower adaptability to environmental shifts. Although stomatal density and size of B. ermanii showed the significant responses to increased temperature and shifting precipitation patterns, the response ranges of stomatal density and size to the environmental factors varied among populations. Our findings highlighted the interplay between genetic and environmental factors in determining the intraspecific variation in stomatal density and size in B. ermanii. This indicated that certain populations of B. ermanii exhibit limited stomatal plasticity and adaptability, which could directly affect photosynthesis and transpiration, suggesting potential population‐specific fitness implications for B. ermanii under future climate change.

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.

Secondary forest accounts for almost 60% of the forest area in Japan. Dwarf bamboo (Sasa senanensis) grows widely in the understory of such forest and could make a significant contribution to the overall CO₂ sink function (gross primary production, GPP) of forest ecosystems. It is, therefore, necessary to evaluate the GPP of Sasa in various forests and estimate its controlling factors. In this study, we estimated the Sasa GPP at the community level by using a chamber system in an evergreen coniferous forest, a mixed forest, and a deciduous broadleaved forest. We hypothesized that (1) the seasonal trends of Sasa community GPP and Sasa annual GPP would differ in different forest types, (2) in addition to light intensity, the seasonal changes of the Sasa community GPP would be controlled by different factors in the different forest types. As a result, although the seasonal trends of the Sasa GPP and the controlling factors differed among the three forests, the annual Sasa GPP was almost the same for the three forests. This study reveals the possible effect of forest type on the seasonal trends of Sasa GPP and its controlling factors; however, for the annual Sasa GPP, the length of the growing periods would also be an important factor.