Indicators of Population Viabllity in Red Spruce, Picea rubens. I. Reproductive Traits and Fecundity
Red spruce (Picea rubens Sarg.) has experienced a substantial decline across most of its range in eastern North America over the past centmy and probably also in the disjunct Ontario populations where it now occurs only in small isolated stands. Measurements of cone and seed traits from natural populations were used as indicators of the reproductive and genetic status of red spruce across the northern margins of its range in Canada. Cone and seed traits were quantified to provide reproductive benchmarks for assessing and monitoring population viability. Reduced fecundity and seedling height growth were observed in some of the smallest Ontario populations, suggesting some inbreeding depression in both vegetative and reproductive components of fimess. Nevertheless, the reproductive status of these small isolated Ontario populations compared favorably with the much larger, more extensive Maritime populations in Nova Scotia and New Brunswick. Significantly higher proportions of aborted (nonpollinated) seeds and lower proportions of tilled seeds suggested poorer pollination conditions in the Maritimes in 19%. The proportion of empty seed, which was used to estimate inbreeding levels, was significantly and negatively related to seedling height growth. In the short-term, the Ontario populations, which probably represent relatively recent remnants of a broader past distribution, generally appeared to be quite resilient to the effects of small population size on fecundity and progeny fitness. In the longer term, continuing decline in population sires and numbers may be expected to erode reproductive success and genetic diversity through the effects of inbreeding, genetic drift, and changes in mating behavior. The reproductive indicators described here have general validity for assessing and monitoring reproductive and genetic aspects of population viability in conifers.