© 2005 Heron Publishing—Victoria, Canada
Growth strain in the trunk and branches of Chamaecyparis formosensis and its influence on tree form
Yan-San Huang (1), Shin-Shin Chen (1, 2), Ling-Long Kuo-Huang (3) and Chin-Mei Lee (1)
1. Division of Forest Utilization, Taiwan Forestry Research Institute, 53 Nan-Hai Road, Taipei, Taiwan 100 / 2. Corresponding author (sschen@serv.tfri.gov.tw) / 3. Department of Life Science, National Taiwan University, 1 Roosevelt Road, Sec. 4, Taipei, Taiwan 106 / Received October 5, 2004; accepted January 15, 2005; published online July 4, 2005
Summary
Distributions of growth strains in branches, straight trunks and basal sweeping trunks of Chamaecyparis formosensis Matsum. trees were measured with strain gauges. Microfibril angles (MFAs) of the S2 layer of the cell wall were measured by the iodine deposition method and their relationships with growth strain examined.
The magnitude of the compressive stress on the lower side of trunks with a basal sweep was greater than that of the tensile
stress at the surface of straight trunks. However, transverse compressive stress was similar around the trunk regardless of
whether normal wood or compression wood was present. The released surface growth strains varied with MFA. At MFAs of 20–25°,
growth stress changed from tension to compression, and compressive stress increased dramatically in the compression wood region.
Branches suffer bending stress due to self-loading. This stress is superimposed on the growth stress. Growth strains on the
upper or lower sides of branches were larger than those in the trunks, suggesting that generation of growth stress on the
lower sides of branches with extensive compression wood is affected by the gravitational bending stress due to self-loading.
We conclude that branch form is affected by the interaction between the bending moment due to self-loading and that due to
the asymmetric distribution of growth stress. Growth strain distribution in a branch differed depending on whether the branch
was horizontal, upward bending or downward bending.
Keywords:
compression wood, microfibril angle, residual internal stress, spring-back strain.
