Within- and between-site variations in leaf longevity in hinoki cypress (Chamaecyparis obtusa) plantations in southwestern Japan

We investigated mean leaf retention time in order to elucidate the factors affecting regional and local variations in stand-level leaf longevity in hinoki cypress (Chamaecyparis obtusa) plantations. Our study sites consisted of six stands at a low elevation (320-370 m a.s.l.) and 12 stands at a high elevation (850-970 m a.s.l.) in southwestern Japan. We also used published data on leaf longevity in stands at various elevations to clarify the regional-scale variations in leaf longevity and their relationships to environmental factors. At the regional scale, leaf longevity increased with increasing elevation and with decreasing air temperature, growing season length, and Kira's warmth index across sites. Similar relationships were obtained for the variation in leaf mass. At the local scale, leaf longevity did not show a clear relationship with topographic position, soil water content, or soil C/N ratio. Contrary to our expectation, leaf longevity was negatively correlated with the leaf C/N ratio at both study sites, although the significance level was marginal. This indicates greater leaf longevity with better leaf nutrient status. Our results suggest that responses of leaf longevity in hinoki cypress stands to environmental factors would be more prominent at the regional scale than at the local scale, although large variation was detected at the local scale. Air temperature and growing season length appear to be the main drivers of the variation in leaf longevity at the regional scale, whereas the causal factors are unclear at the local scale.