Change in the number ratio of overtopped trees in young Sugi (cryptomeria japonica D. Don) plantations

スギ若齢人工林２林分（無間伐林と間伐林）を対象に，劣勢木の本数割合における変化特性を調べた。無間伐林では，相対幹距15.4％以下では劣勢木の本数割合は急激に高くなり，相対幹距15％で8.4％，相対幹距13％で17.2％，相対幹距11％で31.6％と推定された。一方，間伐林では，相対幹距15.4％以下であっても，相対幹距15％で1.9％，相対幹距13％で1.9％，相対幹距11％で7.7％と，無間伐林に比べて顕著に低かった。The changes in the number ratio of overtopped trees over 17 years were investigated in an unthinned and a thinned plantation of young Sugi (Cryptomeria japonica D. Don). The number ratio of overtopped trees in the unthinned plantaiton increased with a decreasing relative spacing index of (Sr)≦15.4%, and was estimated to be 8.4% in Sr=15%, 17.2% in Sr=13% and 31.6% in Sr=11%. In contrast, the number ratio of overtopped trees in the thinned plantation was estimated to be 1.9% in Sr=15%, 1.9% in Sr=13% and 7.7% in Sr=11%, and was much lower than that of trees in the unthinned plantation