MIXED MATING IN AN EXPERIMENTAL POPULATION OF WESTERN RED CEDAR, THUJA-PLICATA

An outcrossing rate of 32% was found in a seed-orchard population of w estern red cedar (Thuja plicata) located on Vancouver Island, British Columbia, This is the lowest outcrossing rate reported for any conifer , in either experimental or natural stands. In addition, this study (a nd another) shows that western red cedar has one-half to one-fourth of the isozyme heterozygosity of other representative conifers. Paleobot anical records indicate this species experienced a severe bottleneck o f population size between 10,000 and 6,000 years BP. This bottleneck m ay have been responsible for these low levels of heterozygosity, which in turn may have decreased levels of inbreeding depression, allowing tolerance of this relatively high level of selfing.