Genetic parameters for wood stiffness and strength properties were estimated in a 29-year-old hybrid larch stand (Larix gmelinii var. japonica × Larix kaempferi). The study included 19 full-sib larch families from Hokkaido, northern Japan. Implications of these genetic parameters in wood quality improvement are subsequently discussed. Traits included in the analyses were the dynamic modulus of elasticity of green logs (E log ), the modulus of elasticity (MOE), the modulus of rupture (MOR), compression strength parallel to the grain (CS) in small clear specimens, wood density (DEN), and diameter at breast height (DBH). DEN had the lowest coefficients of variation and MOE the highest. The narrow-sense heritability estimates of E log , MOE, MOR, and CS were 0.61, 0.44, 0.60, and 0.43, respectively, and those of DEN and all mechanical properties increased from an inner to outer position within the stem. E log and DEN had high positive phenotypic (0.52-0.83) and genetic (0.70-0.92) correlations with MOE, MOR, and CS. The mechanical properties of the inner position of the stem had rather high phenotypic and genetic correlations with those of the outer position and overall mean. The predicted gains in wood stiffness (E log and MOE) were higher than those of the strength properties (MOR and CS). The predicted correlated responses in MOE, MOR, and CS when selecting for E log and DEN were 72.6%-97.8% of a gain achievable from direct selection of these traits. DBH showed an insignificant correlation with all mechanical properties, although selection of this trait had a slightly negative effect on the mechanical properties.

Age trends in the genetic parameters of wood density and the relationship with growth rates in hybrid larch (Larix gmelinii var. japonica ¥ L. kaempferi) F 1 Abstract Age trends in variance components and heritability of overall wood density, earlywood and latewood density, and latewood proportion were investigated in 29-year-old trees of 19 full-sib families of hybrid larch (Larix gmelinii var. japonica × Larix kaempferi) F 1 . The age-age correlation and optimum selection age for these traits were also estimated and genetic and phenotypic correlations between wood density and radial growth rate were calculated for each growth ring. Intraring wood density data were obtained using X-ray densitometry. The coefficient of additive genetic variance was stable over all ages, whereas the coefficient of environmental variances gradually decreased with increasing age, resulting in increases in heritability estimates with age for overall density. The latewood proportion had the highest heritability estimates at all ages, ranging from 0.44 to 0.66. Overall density and its various components at 28 years of age showed strong genetic correlations with their respective traits at all younger ages. Optimum selection ages for the wood density traits ranged from 8 to 14 years, at which point maximum gain efficiencies per year were obtained. There were negative correlations between wood density and radial growth rate at early ages, although these relationships tended to be weaker with increasing age. These results suggest that selection at a young age is effective for wood density, but particular care must be taken in selecting trees with an improved radial growth rate because rapid growth will result in a low-density wood product, especially in the early growth period.

Hybrids generated by crossing Kuril larch (Larix gmelinii var. japonica) and Japanese larch (L. kaempferi) are expected to have high carbon accumulation ability because of fast growth and high wood density in Hokkaido, Japan. We estimated the amount of carbon accumulation of the hybrid larch in three progeny test plantations consisting of 21 full-sib families and compared the results to the carbon accumulation of open-pollinated progenies of Japanese larch plus-trees (improved Japanese larch). Geneenvironment interactions were not observed for tree height and diameter at breast height but were seen for wood density (area-weighted density, AWD). The amount of carbon accumulated per unit area (C stand ) positively correlated with the stand volume. The AWD did not correlate with the C stand ; therefore, families with high wood density can be selected independent of the C stand . The C stand of the best full-sib family, female parent half-sib family, and male parent half-sib family at three sites were 106.1, 84.6, and 93.2 Cton•ha −1 , respectively. All these values exceed the mean for the improved Japanese larch, which has a C stand value of 82.5 Cton•ha −1 .

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Genetic Variation and Genotype-environment Interaction in Annual Ring Structure in Progeny Test of Plus Trees of Sakhalin Fir Abies sachalinensis. J. Jpn. For. Soc. 90: 137 144, 2008 For improving the wood properties of Sakhalin fir Abies sachalinensis variation in annual ring structure and genetic variation in different environments were examined by X-ray densitometry. The specimens were sampled from 32-to 41-year-old open-pollinated families in progeny test stands, which were 74 families totaling 444 trees in Bibai and 24 families totaling 96 trees in Akkeshi. Six components were analyzed as growth ring components-ring width RW , earlywood width EW , latewood width LW , ring density RD , earlywood density ED , and latewood density LD. The values of LW and LD in Akkeshi were smaller than those in Bibai under the influence of low temperature and short sunlight hours in summer. Narrow sense heritability of ring components was 0.17 0.27 for width and 0.26 0.34 for density in Bibai and 0.47 0.79 for width and 0.26 0.66 for density in Akkeshi. The value of heritability of LW and LD in Akkeshi was different for other traits, probably because of the summer weather. The analysis using 23 common families in two stands indicated that interaction between families within provenance and stands was significant in LW, RD, ED, and LD. Therefore, seed zones are as necessary for wood density as resistance to weather damages and disease, or growth.