Persistence and Age-age Genetic Correlations of Stem Defects in Coastal Douglas-Fir (Pseudotsuga menziesii Var. menziesii (Mirb.) Franco)

2000

S. 145-153

4 Abb., 2 Tab., 33 Lit. Ang.

Unselbständiges Werk

200069766

Persistence of stem defects, including bole sinuosity, large branch size and the occurrence of steep-angled branches (i.e., forks and ramicorns), and the efficiency of early selection against these traits, were investigated in 90 open-pollinated families of Douglas-fir (Pseudotsuga menziesii var. menziesii) from coastal Oregon. Trees originally measured for these traits at age 12 were remeasured at age 24 in three progeny test plantations. The majority of trees scored as having ramicorn branches at age 12 (62%) still had them at age 24, but most forks (53%) had become ramicorns by the second measurement. Thus, three seems little need to score forks and ramicorns separately, simply counting the number of whorls with steep-angled branches seems sufficient for selection purposes. Branch size scores were relatively consistent between the two ages, but not scores for bole sinuosity. Because of low estimated individual and family heritability estimates (0.13 and 0.41, respectively), predicted genetic responses in DBH and individual stem-defect traits were only modest for this population. Nevertheless, with the exception of sinuosity, genetic correlations between comparable stem-defect traits at the two ages were strong, and predicted responses in traits at age 24, from selection at age 12, were nearly as great as responses expected if selection was delayed until age 24. Branch size and occurrence of steep-angled branches were unfavorably (positively) correlated with DBH (estimated rA = 0.56 and 0.41, respectively). Thus, it is important to include these stem defect traits as selection criteria in Douglas-fir breeding programs, if stem volume growth is to be improved without sacrificing wood quality.