Genetic variability within Douglas-fir populations: Implications for tree improvement

Genetic variances and covariances for growth potential, phenology and patterns of first year elongation were calculated from 30 half-sib families from each of three contrasting populations. Analyses of 4-year old trees growing in a single environment revealed high levels of additive genetic variance within populations. As a consequence, rather high estimates of genetic gains in growth potential were associated with weak selection intensities. However, genetic correlations were strong. Gains in growth potential were associated with delayed bud set and increased susceptibility to early fall frosts. For tree improvement to increase the growth potential of Douglas-fir without inadvertent degeneration of adaptation, selections must be based on several traits.