Genetic parameters of height and diameter of interior spruce in British Columbia

Data from 406 open-pollinated interior spruce families selected from 3 selection units located in the East Kootenay, Prince George and Prince Rupert region of British Columbia (BC), Canada were used to estimate genetic parameters for cumulative height and diameter (DBH) at plantation ages upto 20 years. Variation among families in both traits was highly significant in all selection units and at all assessment ages, but the levels of genetic variability varied greatly among them. The estimates of individual, family, and within-family heritability for 15-year height ranged from 0.15 to 0.34, 0.61 to 0.84, and 0.12 to 0.28, respectively, among selection units. The corresponding estimates for 20- year DBH varied from 0.10 to 0.23, 0.50 to 0.81, and 0.08 to 0.18, respectively. In all three selection units, temporal variation in individual, family and within-family heritabilities of height displayed parallel patterns and they all started at the highest values at age 3, decreased to the lowest at about age 10, and raised at age 15. Genetic correlation between height and diameter was always positive and impressively strong (0.87 at age 15). The estimated coefficients of age-age genetic correlation in height fit the logarithmic relationships ( rA = a + b (LAR) and rA = a + b (LAR2) very well (R2 0.94) in all selection units but the prediction models of age-age genetic correlation developed in the Prince Rupert selection unit were apparently different from the others. The optimum plantation ages for early selection were calculated to be 15 and 16 years for Prince Rupert selection unit using the LAR and LAR2 prediction model, respectively, and 7 years for both the East Kootenay and Prince George selection units using both models. Overall, the Lambeth model (rA = 1.02 + 0.308 (LAR) developed based on phenotypic correlation of height in Pinaceae tends to underestimate the age-age genetic correlation in interior spruce in BC. Type-b genetic correlation between sites within East Kootenay and Prince George selection units was always positive and strong, but weak positive and even negative correlation was observed between sites in the Prince Rupert selection unit. This observation suggests that the first two selection units may need expansion while the third requires more regionalization for proper breeding and seed planning