Genetic variation in direct and indirect measures of wood stiffness in coastal Douglas-fir

We studied wood stiffness (estimated by modulus of elasticity, MOE), wood density, wood moisture content, and growth in a progeny test (50-130 families per trait; 1-3 sites) of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco). We measured MOE directly using lumber bending tests (MOEbl) and indirectly using tools (HM200 and ST300) that can be used to measure acoustic velocity in logs (Vel(HM)) or standing trees (Vel(ST)). Acoustic MOEs in logs and standing trees (MOEHM and MOEST) were obtained from the velocities and green wood density. For backward selection, we estimated genetic gains in MOEbl of 8.6%-12.3%. Relative efficiencies (REs), the relative gains in MOEbl expected from indirect selection for correlated traits, were 78%-93% for the HM200 traits, 57%-58% for the ST300 traits, 38% for the basic wood density of basal discs (Denbd), and 98% for the oven-dry density of logs estimated from the lumber (Den(ol)). The HM200 is an efficient tool for improving MOEbl, but gains will be lower using the ST300 on standing trees. Indirect selection on Denbd should be used with caution because the RE was low and Denbd was negatively correlated with growth (-0.49 to -0.73).