Determination of relative economic weights for multitrait selection in coastal Douglas-fir

Relationships between tree traits and tree value for lumber production were investigated. For the purposes of estimating relative economic weights for use in multitrait selection in coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) France var. menziesii), tree height, diameter at breast height, and branch diameter were measured on 164 trees (ages 36-66 years). Increment cores from a subsample (92) of these trees were assayed by X-ray densitometry to determine wood density. Bole volume was derived by summing the log volumes of all logs from each tree. Value of lumber recovered from each tree was determined in a separate mill study using both visual and machine stress rated (MSR) grading rules. Multiple linear regression was used to relate tree value to the growth and wood quality traits. Stem volume and branch diameter significantly influenced tree value under visual grading, with relative economic weights of 0.06 dm(3) and -5.22 cm, respectively. Wood density significantly influenced tree value under MSR grading (relative economic weights: 0.06 dm(3), -6.69 cm, and 0.06 kg/m(3), respectively), where lumber strength is measured more accurately. These regression coefficients can be used directly as economic weights in selection indices.