Genetic Implications of Shelterwood Regeneration of Douglas-fir in Southwest Oregon

Abstract

Abstract The genetic structure of two Douglas-fir ( Pseudotsuga menziesii var. menziesii ) shelterwood stands in southwest Oregon was investigated. With the exception of the Lap2 locus in one shelterwood, estimated frequencies of alleles at ten allozyme loci were not significantly heterogeneous among population samples from (1) uncut stands adjacent to shelterwoods, (2) shelterwood leave trees, (3) seed crops in shelterwoods, and (4) 3- to 5-year-old regeneration in shelterwoods. Measures of genic diversity (mean number of alleles per locus, percentage of polymorphic loci, and mean expected heterozygosity) were also not significantly heterogeneous among the four life-cycle stages. Contingency chi-square tests and estimates of the fixation index indicated that the observed genotypic proportions rarely differed significantly from those that were based on Hardy-Weinberg expectation at all life-cycle stages. The relative invariance of allele frequencies among stages and the absence of detectable inbreeding within them was attributed to high within-stand heterozygosity, high outcrossing rates, and large effective population size. Forest Sci. 31:995-1005.