抄録
The forest stratification and species diversity of the old-growth Cryptomeria japonica D. DON natural forests on Yakushima were studied. Five fine-scale permanent plots of 0.80-1.00ha were established in these forests, and the height and DBH of all living trees were measured twice with intervals of 15-19 years. Using the discriminant analysis method, each plot was stratified into two strata and the degree of stratification was quantified. The upper and lower strata were almost entirely composed of coniferous and broad-leaved species, respectively. The difference in the intensity of past cutting was considered to have affected the species diversity. The recruitment, mortality and stratification patterns showed that the regeneration of coniferous species might depend on the occurrence of large canopy gaps due to typhoons. The stability of the maximum tree height suggested that the typhoons limited the maximum tree height. A negative correlation between the degree of stratification and species diversity was observed, indicating that the degree of stratification was indirectly affected by the effect of past cutting on species diversity. From these results, it was concluded that both artificial disturbance due to cutting and natural disturbance due to typhoons played an important role in the dynamics of forest stratification and species diversity of C. japonica natural forests on Yakushima.
