In situ wood quality assessment in Douglas-fir

The genetic control and phenotypic and genotypic correlations among wood density, modulus of elasticity, height, diameter, and volume were assessed using 967 trees representing 20 unrelated 32-year-old coastal Douglas-fir full-sib families growing on four (spaced and pruned vs. control) comparable test sites. Generally, no significant differences were observed between treatments, indicating their limited effect at assessment time. Family effect did not differ for the growth traits; however, significant differences were observed for wood density and both in situ methods (drilling resistance and acoustic velocity). Growth and wood quality attributes, individually, produced high and positive phenotypic and genetic correlations; however, high and negative correlations were observed between individual variables belonging to the two suites of attributes. Individual tree heritabilities were low for growth (0.04 to 0.08) and modest to high for wood quality attributes (0.14 to 0.68). The observed heritabilities and phenotypic and genotypic correlations imply modest to strong genetic control; however, they operated in opposing direction. The significant and consistent genetic correlations between the in situ methods and wood density and stiffness support their use as a non-destructive and economic assessment approach. The reliability of the in situ assessments was verified through cumulative pith-to-bark wood density assessment, resulting in inconsistent genetic and phenotypic correlations for early growth years. These latter findings imply that caution should be used in employing these in situ techniques as early screening tools in breeding programs.