Thinning Effects on Changes in Crown Length and the Increment in Diameter at Breast Height of Japanese Cedar Trees in Overcrowded Mature Plantations.

The effects of moderate low thinning of around 30％ in number ratio on changes in crown length for seven years and DBH growth for four years were investigated in overcrowded mature plantations of Sugi (Cryptomeria japonica D. Don). Mean crown length increased with time in the thinned stands. In the thinned stands, mean height increment was approximately 0.2 m/year, while the rising rate of crown base was nearly 0.0 m/year. Mean DBH increment in the thinned stands was significantly higher than that in the unthinned stand. As for the relationship between initial DBH and DBH increment, the greater the initial DBH, the greater the difference in the increment between the thinned stands and the unthinned stand. There are cases in which the rise of crown base in overcrowded mature stand can be stopped even by moderate low thinning. However, thinning effect on DBH growth would decrease, as the trees which are comparatively suppressed among inter-tree competition. © 2022 Nihon Ringakkai. All rights reserved.