Factors responsible for co-dominance of two beech species in a cool temperate forest in central Japan: interspecific comparison of spatial distribution and growth traits

To understand the co-existence mechanisms of related species,the recruitment processes of Fagus crenata and F. japonica were censused during 3 and 4 years from emergence, respectively, in a cool-temperate forest in Japan. The distributional properties and the growth traits were compared between two Fagus species. To evaluate the distributional properties, the spatial abundance of seedlings was estimated by a generalized linear model (GLM), with explanatory variables such as topographic variables, light conditions, the presence of dwarf bamboo, and the abundance of the overstory. To evaluate the growth traits under herbivory pressure, both the elongated shoot length and the proportion of recovery frompredation (re-growth) were also compared. No spatial segregation and no species-specific differences were detected by GLM, which was consistent throughout the census period. Only F. japonica exhibited a slope-related distribution, while F. crenata exhibited no topographical dependence, indicates the distributional overlaps. For the growth traits, contrasting trends were detected, F. crenata was superior in shoot growth, whereas the proportion of regrowth was higher in F. japonica than F. crenata. We concluded that co-dominance of these species was not attributed to the spatial segregationbut to the trade-off between growth and resistance to herbivory