Genetic parameters of growth and stem forking for black spruce progeny tested in New Brunswick, Canada

We investigated genetic parameters for juvenile to mature growth and stem forking in black spruce [ Picea mariana (Mill.) B.S.P.] in order to obtain reliable estimates for supporting eastern Canadian tree breeding strategies. The study was based on data collected from two series of progeny tests of black spruce in New Brunswick (NB) including 285 open-pollinated families and more than 57,000 individual trees. Height (HT), diameter at breast height (DBH), and stem forking (SF) were periodically measured between ages 5 and 35 years. Results showed that tree volume (V), HT and DBH were highly genetically controlled, with average individual narrow-sense heritability ( h i 2 ) estimates of 0.29, 0.29 and 0.21, and family mean heritability ( h F 2 ) estimates of 0.82, 0.85 and 0.77, respectively. SF had low h i 2 (= 0.06 on average) but had moderate h F 2 (= 0.56), indicating family selection might effectively reduce SF. Both h i 2 and h F 2 increased with age and then stabilized or declined, being the highest around ages 15–20 years for all traits. The type-B genetic correlation ( r B ) estimates were moderate to high for all the traits, suggesting negligible genotype × environment interactions. Strong age–age genetic correlation estimates were found for growth traits, implying the potential for practicing early selection. Age–age genetic correlation estimates were moderate for SF (= 0.72). Trait–trait genetic correlation estimates were strong and positive among growth traits, but between growth traits and SF they were mostly negligible albeit positive. Overall, results suggest that genetic selection will be effective for growth traits but much less so for reducing stem forking in New Brunswick’s black spruce.