Abstract
The distribution of growth strain in basal sweeping trunks of Chamaecyparis formosensis Matsum. was measured by the kerf method using strain gauges. Effects of both tree height and peripheral positions on the trunk on the released surface strains were examined. The residual internal growth strains were also measured. The microfibril angles (MFAs) of the S2 layer of cell wall were measured using the iodine deposition method to examine their influences on growth strain. The results showed that there was no obvious relationship between tree height and growth strain. We found large compressive stresses on the lower side of sweeping trunks that differed greatly from the tensile stresses in normal erect trunks. Regarding the residual internal stresses within erect trunks, contract strain or tensile stress was present toward the outside, whereas extension strain or compressive stress was induced toward the inside of the trunk. The MFA of compression wood was larger than that of normal wood. Branches suffered bending stresses due to their own weight. This stress was 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 was shown that the growth strain increased with an increase in the spring-back strain on the lower side of branches, and the former was obviously larger than the latter. This suggests that the generation of growth stresses on the lower side of branches containing highly developed compression wood is affected by the gravitational bending stress due to their own weight. It was concluded that the branch form is affected by the interaction between the bending moment due to its own weight and that due to growth stresses.