SELECTION OF CROWN FORM TRAITS IN CONTROLLED CROSSES OF COASTAL DOUGLAS-FIR

Genetic parameters for crown-form traits and bole taper were investigated in full-sib progeny of Douglas-fir (Pseudotsuga menziesii (MIRB.) FRANCO). Significant amounts of additive genetic variance were shown for all traits except branch thickness. Non-additive genetic variance was statistically significant (p < .05) for three of the eight crown from traits investigated. High individual-tree heritability was expressed for branch angle, indicating that this trait could be improved through phenotypic selection. Progeny testing would be more effective for most other form traits. Branch thickness and branch length indicate stronger genetic differences when they are expressed as a proportion of stem size. A positive association existed between yield and a fine branching form type. Path-analysis showed that branch number was associated with 42% of family differences for stem volume. Multi-trait index selection can be used to improve both yield and fine branching in Douglas-fir seed orchard progeny.