Growth stress distribution in leaning trunks of Cryptomeria japonica

The distribution of growth stresses in leaning trunks of Cryptomeria japoni ca (L.f.) D. Don was determined by measuring the stresses released by the k erf method with strain gauges glued at specified positions along the trunks . Effects of both tree height and peripheral positions on the surface of le aning trunks on surface growth stress were determined. The inner residual g rowth strains in leaning trunks were also measured. We found high compressi on stresses in the lower side of leaning trunks that differed greatly from the tensile stresses in normal erect trunks. However, transverse compressio n stress was found around the tree trunk in both normal and compression woo d. In leaning trees, the distribution of internal stresses in the bent trun k portion differed from that in the erect trunk portion, being compressive on the outside and tensile on the inside. The resistant moment introduced b y compression stress generated in compression wood is released by the bendi ng of the leaning trunk. The bending stresses are then superimposed on the original internal growth stress. We demonstrated that Poisson's effect of l ongitudinal stresses should be considered when evaluating transverse surfac e growth stresses. The existence and intensity of compression wood developm ent can be assessed by growth stress measurements. We conclude that the com pressing force of compression wood functions physiologically to give an upw ard righting response in a leaning trunk.