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(ML) recovery of the estimated means and variances of the expected completed samples. ML
estimates became increasingly stable as truncation proceeded into the main body of data. Prior to
data truncation, the estimated additive variance and heritability estimates of the CP population
were significantly greater than corresponding estimates for the OP population. However, ML
estimates obtained after a proportional elimination of about 12% of the trees in each plot
supported the contention that there was no important difference in additive genetic variance or
heritability between OP and CP populations.
355. Magnussen, S. and A.D. Yanchuk. 1993. Selection age and risk: finding the compromise. Silvae-
Genetica 42(1): 25-40.
Keywords: genetic tree improvement
growth
Abstract: Selection ages for height in coastal Douglas-fir (Pseudotsuga menziesii) at four
sites on Vancouver Island, Canada, were determined by stochastic simulation of age-to-age
correlations. Stochastic perturbations of expected age-to-age correlations at both family and
within-family levels were derived from bootstrapping more than 4000 records of 23 years of
observed height growth. Stochastic dominance principles were used to isolate stochastic efficient
(risk averse) selection ages in both family and forward selection schemes. The optimum age for
family selection depended strongly on the number of progenies tested in each family and on the
test site. Early family selection (age