Abstract
Past management, stand structure and tree quality composition were investigated in six stands of about 100-year-old Chamaecyparis obtusa plantations, to understand the effects of their respective thinning histories. The stand which had not been thinned for about 60 years since the previous thinning showed highest tree density (843 trees ha−1) and highest stem volume (1,298.9 m3 ha−1), and tree density and stem volume tended to decrease as the frequency of thinning increased. Maintaining lower tree density, that is, less than 500∼1,000 trees ha−1 from the early stage of the plantations, may enable the establishment of an old-aged coniferous plantation with high stem volume, without additional thinning. On the other hand, regarding tree quality composition, planted trees belonging to larger size-classes showed a higher proportion of higher quality trees in all stands. However, lower quality trees were observed even in the stands which had been subjected to multiple thinnings. Tree density of the higher quality trees was constant, at 100∼150 trees ha−1 in all the stands, regardless of the thinning history. These results suggest that the thinning in the study stands had not improved the quality composition of the stands. The data in this study could not provide much background information about this, they may nonetheless be important for establishing old-aged coniferous plantations composed of higher quality trees by thinning lower quality trees at the early stage of the plantations.
