Early selection for wood density in young coastal Douglas-fir trees

Abstract

Selection age for wood density in vigorous coastal Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) was determined by examining the following: strength of the correlation between total-stem wood density of 50-year-old trees and their breast-height density when the trees were 5 through 30 years old (breast-height age); efficiency in terms of gain per year of tree improvement effort by selecting at ages 5 through 30, relative to selecting at age 50. The linear regression and rank correlation between total-stem and breast-height densities improved as age increased from 5 to 15 years, but showed no significant improvement from 15 to 30 years. Densities of early-growth rings fluctuated considerably and their exclusion from the calculation of breast-height density enhanced the linear regression with total-stem density. Efficiency estimates in terms of gain per year showed an optimum value at age 15, but the estimates for ages 10–14 were nearly as efficient.