In perennial plants, such as trees, reproduction event affects individual-level resource allocation. In some tree species, vegetative growth is markedly reduced in a large reproduction year (e.g., heavy masting year). In Fagus crenata, growth usually starts at the beginning of growing season, but seed ripening occurs later in the growing season. Therefore, there are two hypotheses that could explain the mechanism for growth reduction in a masting year; 1) reduction of growth rate due to resource allocation both to vegetative growth and reproduction during the growing season, and 2) early growth saturation due to switching of the resource allocation from vegetative growth to seed ripening. In this study, we aimed to evaluate the effect of masting on the trunk radial growth of F. crenata from the point of view of the resource allocation. High-resolution
patterns of radial growth in F. crenata during a non-reproduction year (2014) and a heavy-masting year (2015) were monitored by using a digital dendro-meter.
Data from digital dendro-meter were fitted to a sigmoidal function, and the parameters of the function were evaluated using the hierarchal the Bayesian approach as the properties of the seasonal trunk radial growth pattern. Trunk radial growth in each individual of the F. crenata started synchronously just after leaf flushing in both non-reproduction (2014) and a heavy-masting years (2015), but slightly earlier in the heavy masting year. The reproduction affected negatively the radial growth rate. The growing period of the trunk growth varied among individuals in both years, and there was not any clear difference between the reproductive and non-reproductive trees. During the trunk radial growing period, branch and cupula biomass also increased, and seed weight started increasing after branch and cupula biomass increasing were settled. As these results, trunk radial growth was larger in non-reproductive trees than in the reproductive trees in the heavy reproduction year. These results suggest that the decrease in trunk radial growth of F. crenata in a masting year resulted from the reduction of growth rate.