Original paper(Vol.49 No.4 pp.379)

Effect of growth rate on the growth strain in Cryptomeria japonica

Kitahara Ryushi; Sakaida Tsuyoshi; Haruyama Katsuaki

Abstract:Growth stresses occur in the stem of living trees. They frequently cause considerable degradation of timber based on end-splittings and warps of logs and boards after felling or during machining. This paper examined the influence of rate of growth in stem diameter on peripheral longitudinal and internal longitudinal growth strains in 22, 25 and 30 years old plantation grown trees of Cryptomeria japonica. The relationship between peripheral longitudinal growth strain and wood properties was also investigated. Strain due to growth stress relief was measured by using electronic strain gauges glued to the outer xylem and within stem xylem. In addition to, set recovery (that is, dimensional change) due to growth stress relief within logs was measured by using a length comparator after heat treatment.
A negative correlation was found between level of growth strain and rate of growth in diameter in silviculturally treated trees. Lower average levels of growth strain occurred in trees with higher growth rate. The internal longitudinal strain gradient, along a radius from pith to outer xylem, was reduced in trees with a faster rate of growth. As such, less splitting and warp during conversion would occur in faster grown trees. Moreover, the fact that peripheral growth strain was lower in trees with higher wood density, longer tracheid length and smaller mean microfibril angle suggested that splitting and warp due to growth stress relief would be decreased by using silvicultural treatments.

Key Words:Growth strain, Rate of growth, Cryptomeria japonica, Growth strain gradient, Set recovery, Wood properties