The mating system in natural populations of western redcedar (Thuja plicata)

Outcrossing rates and the correlation of paternity were estimated in six na tural populations of western redcedar (Thuja plicata Donn. ex D. Don) in so uthwestern British Columbia. Over 3000 offspring were assayed, as progeny a rrays, for the only sufficiently polymorphic isozyme locus in this species, glucose-6-phosphate dehydrogenase. Estimates of population outcrossing rat es ranged from 0.173 to 1.257 and averaged 0.715 +/- 0.045 (mean +/- SD). E stimates of the correlation of paternity generally did not differ from zero . Six of the seven outcrossing estimates (one population was surveyed in tw o consecutive years) were higher than a previous seed orchard study. Howeve r, these outcrossing rates are still lower than those estimated for most ot her species of conifers. Population outcrossing rates also showed wide vari ation, and this variation is discussed in terms of ecological and phenologi cal differences among populations.