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

Outcrossing rates and the correlation of paternity were estimated in six natural populations of western redcedar (Thuja plicata Donn. ex D. Don) in southwestern British Columbia. Over 3000 offspring were assayed, as progeny arrays, for the only sufficiently polymorphic isozyme locus in this species, glucose-6-phosphate dehydrogenase. Estimates of population outcrossing rates ranged from 0.173 to 1.257 and averaged 0.715 ± 0.045 (mean ± SD). Esti- mates of the correlation of paternity generally did not differ from zero. Six of the seven outcrossing estimates (one population was surveyed in two consecutive years) were higher than a previous seed orchard study. However, these out- crossing rates are still lower than those estimated for most other species of conifers. Population outcrossing rates also showed wide variation, and this variation is discussed in terms of ecological and phenological differences among popu- lations.