Abstract
Abstract
The aim of this study is to preliminarily clarify the wood properties and lumber qualities of trees of male-sterile
Cryptomeria japonica
full-sib families, and to evaluate the possible short-rotation forestry using these families, although the number of trees and families used in this study is limited. The standing tree characteristics, wood properties, and dimensional lumber quality (1820 × 38 × 89 mm; visual grading according to the Japanese Agricultural Standards for structural lumber and finger jointed structural lumber for wood frame construction [JAS 0600], and static bending properties) were investigated in 14-year-old trees (12-year-old forest stand) from five male-sterile
C. japonica
full-sib families developed by the Tokyo Metropolitan Agriculture and Forestry Research Center, Tokyo, Japan. The mean values of stem diameter at 1.2 m above the ground, tree height, and stress-wave velocity of stems in all 22 trees from five families were 15.2 cm, 12.3 m, and 2.45 km/s, respectively. Mean value was also 7.7 mm in annual ring width, 0.31 g/cm
3
in basic density, 26.9° in microfibril angle, 5.60 GPa in modulus of elasticity (MOE), and 58.7 MPa in modulus of rupture (MOR). In lumber quality (
n
= 34), annual ring width, bow, crook, twist, slope of grain, air-dry density, MOE, and MOR were 9.4 mm, 0.28%, 0.18%, 1.4°, 0.09%, 0.37 g/cm
3
, 4.79 GPa, and 33.4 MPa, respectively. Although the lumber was obtained from 14-year-old trees, about 90% of lumber pieces exceeded the characteristic value of MOR (28.4 MPa) in the select structural visual grading class of JSII of JAS 600. In addition, the preliminary calculated value of the 95% lower tolerance limit with a confidence level of 75% of the MOR of lumber was 23.1 MPa. Therefore, from the viewpoint of the bending properties of lumber, short-rotation
C. japonica
forestry producing structural lumber might be established, owing to the improvement of mechanical properties by tree breeding in male-sterile families, although the tested samples were limited.