Indicators of population viability in red spruce, Picea rubens. I. Reproductive traits and fecundity

Red spruce (Picea rubens Sarg.) has experienced a substantial decline acros s most of its range in eastern North America over the past century and prob ably also in the disjunct Ontario populations where it now occurs only in s mall isolated stands. Measurements of cone and seed traits from natural pop ulations were used as indicators of the reproductive and genetic status of red spruce across the northern margins of its range in Canada. Cone and see d traits were quantified to provide reproductive benchmarks for assessing a nd monitoring population viability. Reduced fecundity and seedling height g rowth were observed in some of the smallest Ontario populations, suggesting some inbreeding depression in both vegetative and reproductive components of fitness. Nevertheless, the reproductive status of these small isolated O ntario 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 fill ed seeds suggested poorer pollination conditions in the Maritimes in 1996. 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 r ecent remnants of a broader past distribution, generally appeared to be qui te resilient to the effects of small population size on fecundity and proge ny fitness. In the longer term, continuing decline in population sizes and numbers may be expected to erode reproductive success and genetic diversity through the effects of inbreeding, genetic drift, and changes in mating be havior. The reproductive indicators described here have general validity fo r assessing and monitoring reproductive and genetic aspects of population v iability in conifers.