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previous generation. The removal of the smallest trees to form shelterwoods resulted in the
removal of rare, presumably deleterious, alleles. Fewer alleles per locus were observed among
residual trees (2.76) and natural regeneration (2.75) than were found in uncut (control) stands
(2.86). The shelterwood regime appeared quite compatible with gene conservation, and it was
considered that it was best to leave parent trees of a range of sizes to act as gene conservation
reserves, in order to maximize the number of alleles (regardless of current adaptive value) in
naturally regenerated offspring. Seedling stocks used for artificial regeneration in clearcut,
shelterwood, and group selection stands (7 total) had significantly greater levels of genetic
diversity, on average, than natural regenerated seedlings.
12. Aitken, S.N. and W.T. Adams. 1996. Genetics of fall and winter cold hardiness of coastal
Douglas-fir in Oregon. Canadian-Journal-of-Forest-Research 26(10): 1828-1837.
Keywords: genetic tree improvement
tree/stand protection
tree/stand health
tree physiology
genetic relationships
Abstract: Genetic variation in autumn cold hardiness was studied in two western Oregon
breeding populations of coastal Douglas fir (Pseudotsuga menziesii var. menziesii), one on the
west slope of the Cascade Mountains and the other in the Coastal Range. On six sampling dates
(September, October and November 1992 and January, September and October 1993), shoot
cuttings from 40 open-pollinated families in each of two progeny test sites for each breeding zone
were subject to artificial freezing at two test temperatures. Damage in each shoot was recorded as
visible injury to needle, stem and bud tissue separately. Considerable family variation was found
for cold injury scores in all tissues in early to mid autumn, but differences were often smaller or
nonsignificant in late autumn and midwinter. Individual heritability estimates for needle cold
injury were low (