Abstract
To determine suitable conditions for the establishment of Pinus densiflora seedlings on Daimonji-yama Mountain, Kyoto, Japan, five experimental sites were established in forests with pine wilt disease, after first removing the major broadleaf trees and litter. Plots in each site were 1 m2 and were subjected to one of the following treatments: treatment 1, the A0 layer was removed; treatment 2, two levels of horizontal terraces were created after removing the A0 layer; and control, no additional work was done. In the second year after P. densiflora seeds had been sown in each plot, the seedlings in the two treatment plots showed higher emergence, higher survival rates, and more vigorous growth, but a smaller top-to-root ratio than those of the control group, while the differences among the two treatments were not significant. These results indicate that removing the A0 layer enhanced root development in the mineral soil layer, as well as decreasing the mortality rate caused by drought and bacterial infection. In the fourth year, seedling growth in the control and treatment 2 declined considerably compared to treatment 1. In control, recovery of understory vegetation occurred, while in treatment 2, invasion of Gleichenia japonica was observed. The decline in growth rates in these two groups can be attributed to the vigorous understory vegetation that inhibited seedling growth. In summary, our study shows that removing the A0 layer and the broadleaf tree cover can be effective in improving the establishment, seedling growth, and subsequent regeneration of P. densiflora at this study site. However, seedling growth was inhibited by the creation of terraces (treatment 2) which may promote the growth of understory vegetation.
