Growth strain in the trunk and branch of Chamaecyparis formosensis Matsum. and its influence on tree form

The distribution of growth strains in the branch and the basal sweeping trunks of Chamaecyparis formosensis Matsum. was measured using strain gauges. The microfibril angles (MFAs) of the S2 layer of cell wall also were measured by the iodine deposition method to examine their relationships with the growth strain. We found that the magnitude of the compressive stress on the lower side of sweeping trunks was greater than that of the tensile stresses in straight trunks. However, transverse compressive stress was found to be similar around the trunk regardless of normal and compression wood. The released surface growth strains varied with the variation of MFAs. The growth stress changed from tension to compression at 20∘~ 25∘, and the compressive stress increased dramatically in the compression wood region.
Branches suffer bending stress due to its self-weight. This stress is then superposed on the growth stress. It was found that growth strains on the upper side or lower side of branches were larger than those in the stems. It suggests that the generation of growth stress on the lower side of branch containing highly developed compression wood is affected by the gravitational bending stress due to its self-weight. We concluded that the branch form is affected by the interaction between the bending moment due to its self-weight and that due to the asymmetric growth stress distribution. Three types of branches, that is, horizontal (or slant), bending upwards and bending downwards, showed different status of growth strain distribution in branch.