The mating system in natural and shelterwood stands of Douglas-fir

Mating systems in two pairs of old-growth uncut and adjacent shelterwood stands of Douglas-fir (Pseudotsuga menziesii var. 'menziesii') were compared by estimating the proportions of viable progenies due to outcrossing (t) with both single-locus and multilocus techniques. Single-locus population estimates (ťs), ranging from 0.41 to 1.16, were significantly (P<0.05) heterogeneous among loci in three of four stands; mean single-locus estimates for shelterwoods were not significantly different from those for uncut stands. Multilocus population estimates (ťm) ranged from 0.94 to 1.00; again, estimates for shelterwoods were not significantly different from those for uncut stands. Multilocus estimates were slightly higher than mean single-locus estimates for uncut stands but were nearly equivalent for shelterwoods, suggesting that related matings other than selfs may be associated with uncut stands, but not shelterwoods. Individual-tree outcrossing rates (ťm i), estimated for six trees in each shelterwood, ranged from 0.90 to 1.10 and were significantly heterogeneous among trees at one of the two shelterwoods. Outcrossing was high (> 0.90) in both uncult and shelterwood stands, and no evidence indicated that low parent-tree density had affected stand outcrossing rates.