紅檜造林木樹幹與枝條之生長應變探討

Growth Strains in Trunks and Branches of Planted Chamaecyparis formosensis Matsum.

陳欣欣(Shin-Shin Chen) ； 黃玲瓏(Ling-Long Kuo-Huang) ； 李金梅(Chin-Mei Lee) ； 黃彥三(Yan-San Huang)

《台灣林業科學》 21卷2期 (2006/06) Pp. 263-272

https://doi.org/10.7075/TJFS.200606.0263

摘要

樹枝承受來自自重之彎曲應力，此一應力與生長應力重疊。樹枝上下側之生長應變較樹幹者為大。枝條下側之生長應變有隨反彈應變之增大而增大之趨勢，且前者大於後者。吾人認為樹枝下側抗壓材所產生之壓縮生長應力係受到由自重所引發之重力彎曲應力之影響。因此，抗壓材所引起之高壓縮應力係與重力刺激有關。樹枝形態受樹枝自重所引起之彎距與生長應力所引起之彎距二者間之交互作用的影響。樹皮之生長應變測定結果顯示不論樹幹或樹枝均為收縮生長應變，顯示有引張生長應力之存在。
本研究係利用應變規以刻溝法測定紅檜(Chamaecyparis formosensis Matsum.)造林木根曲樹幹之生長應變，探討樹高及圓周位置對解放表面生長應變之影響，同時亦測定樹幹內部殘留生長應變，木質部細胞壁S2層之微纖維傾斜角(microfibril angle，MFA)與生長應變之關係亦被探討。試驗結果顯示生長應變與樹高間無明顯相關性，根曲樹幹下側有很大的壓縮生長應力，抗壓材之MFA遠大於正常材者。

關鍵字

抗壓材 ； 微纖維傾斜角 ； 生長應變 ； 反彈應變 ； 內部殘留應變

並列摘要

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.

並列關鍵字

compression wood ； microfibril angle ； growth strain ； residual internal stress ； spring back strain