Cross-sectional Area Increment of the Lower Trunk in Aged Sugi (<i>Cryptomeria japonica</i>) Trees: A Heightening Trend

The vertical distribution of the cross-sectional area increment lower trunk in aged Sugi (Cryptomeria japonica) trees was analyzed using annual ring data from disks. We collected three approximately 90-year-old mature plantations under different density management and old-growth stands 160 years or more. Of nine sample thinning experiment plots, only had significantly higher increments at a relative height 0.2 × tree (0.2h) than mean increment. This result did not strongly support hypothesis that several are thinned regularly may show heightening trend trunk. In contrast, 0.2h for all stands. A generalized linear mixed model with presence absence as response variable used 20 trees. results showed ratio to diameter breast (H/D ratio) spacing index (Sr) fixed effects optimal. probability showing increased H/D Sr most recent values. estimated if stand is maintained an Sr≥19%, where forest canopy sparse, part occurs ≤71.