The Mating System of Black Spruce in North-Central Alberta, Canada

Summary Mating system parameters for a lowland and an upland black spruce population were simultaneously estimated for the 1983, 1982 and 1981 seed years, and for bulked seed collections from the 1978 to 1976 seed years. Population multilocus outcrossing estimates increased from 0.62 in 1983, to 0.85 in 1978 to 1976. There were no significant differences in outcrossing estimates among populations, or between years, although there was a significant difference between the most recent (1983) and the oldest estimate (1978 to 1976). Single-locus outcrossing estimates ranged from 0.326 to 1.03 with significant heterogeneity amongst loci in all 3 years in the lowland site, but with only the 1981 population showing significant heterogeneity in the upland site. Correlation between stand density, assessed from fixed-area plots, and the multilocus outcrossing estimate from each plot was not significant in either population. Three factors suggested population substructuring: (i) Means of single-locus estimates of outcrossing for each year were consistently lower than multilocus estimates. (ii) There was significant spatial heterogeneity of the outcross pollen pool. (iii) WRIGHT’s Index of Fixation was higher than the inbreeding equilibrium coefficient.