© 2001 Heron Publishing—Victoria, Canada
Growth stress distribution in leaning trunks of Cryptomeria japonica
Yan S. Huang (1), Shin S. Chen (1), Tsan P. Lin (2) and Yuh S. Chen (1)
1. Division of Forest Utilization, Taiwan Forestry Research Institute, 53 Nan-Hai Road, Taipei 100, Taiwan / 2. Division of Silviculture, Taiwan Forestry Research Institute, 53 Nan-Hai Road, Taipei 100, Taiwan / Received March 10, 2000
Summary
The distribution of growth stresses in leaning trunks of Cryptomeria japonica (L.f.) D. Don was determined by measuring the stresses released by the kerf method with strain gauges glued at specified
positions along the trunks. Effects of both tree height and peripheral positions on the surface of leaning trunks on surface
growth stress were determined. The inner residual growth strains in leaning trunks were also measured. We found high compression
stresses in the lower side of leaning trunks that differed greatly from the tensile stresses in normal erect trunks. However,
transverse compression stress was found around the tree trunk in both normal and compression wood. In leaning trees, the distribution
of internal stresses in the bent trunk portion differed from that in the erect trunk portion, being compressive on the outside
and tensile on the inside. The resistant moment introduced by compression stress generated in compression wood is released
by the bending of the leaning trunk. The bending stresses are then superimposed on the original internal growth stress. We
demonstrated that Poisson's effect of longitudinal stresses should be considered when evaluating transverse surface growth
stresses. The existence and intensity of compression wood development can be assessed by growth stress measurements. We conclude
that the compressing force of compression wood functions physiologically to give an upward righting response in a leaning
trunk.
Keywords:
compression wood, residual internal stress, surface growth strain, strain gauge.
