Mechanical properties affecting the within-tree variation of microfibril angle

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Microfibri angle (MFA) is large in the juvenile wood within stem, and is different by species and clones within the same species. It suggests that MFA is genetic component, but also it is affected by a factor changing by tree growth such as tree mechanical properties. Tree structure including the root system was examined, and the wood properties were compared between the stem and branch wood formed under gravitation and the root wood formed under gravity-free state, using sugi (Cryptomeria japonica) clones having different MFA and spruce having small MFA. The root systems were different by clones or species having different MFA and strength properties in the stem. The MFA difference between young sugi clones were large in the stem wood, but small in the root wood, which suggested that the large MFA variation in the sugi juvenile wood is observed only above the ground. The root wood was eccentric, didn't form the compression wood and its growth stress distribution was not symmetric about the center.