Genetic parameter estimates for growth traits of black spruce in northwestern Ontario

Abstract

Genetic parameters of growth traits were estimated for first-generation selections of black spruce ( Picea mariana (Mill.) BSP) in northwestern Ontario from 720 open-pollinated families and more than 42 000 trees. Unbiased estimates of narrow-sense heritability for tree height growth averaged 0.19, 0.18, and 0.14 at ages 6, 11, and 19 years, respectively, from combined-site analyses compared with 0.25, 0.23, and 0.16 for the same ages from single-site analyses. Heritability estimates for diameter at breast height and stem volume were lower than that of height at age 19, suggesting that tree height is a more desirable trait for selection in black spruce. The moderately high estimates of type B genetic correlations implied limited operational importance of genotype × environment interactions. Estimates of age–age genetic correlation were high (>0.88) among cumulative tree height growth at 6, 11, and 19 years but lower between height increments from different age intervals. Estimates of type B age–age genetic correlation were more than 0.2 lower than their type A counterparts, suggesting strong effects of common environments on the estimates of type A genetic correlations. Based on the relative selection efficiencies, selection on cumulative tree height between ages 6 and 11 was more efficient than at age 19.