Red spruce (Picea rubens) populations in the southern Appalachians (Tennessee, North Carolina, Virginia) are disjunct from larger northern populations in New York, Vermont, New Hampshire, Maine and Canadian Maritime provinces. Heavy logging followed by severe fires in the early 20th century resulted in a > 90% reduction in spruce-fir forests in the southern Appalachians. The remaining red spruce populations are highly fragmented and restricted to high elevations. Considering their adaptation to cool, humid environs, they have the potential to become maladapted with predicted climate change. To assess existing populations for adaptive traits (phenology, physiology) we collected seed from several populations in North Carolina, Tennessee, and Virginia (half-sib) with the goal of propagating seedlings and identifying phenotypic differences in common garden plantings. Seed was collected from 15 trees in 2015 and 115 trees in 2016 from elevations ranging from 1036 to 1988 m. Red spruce produces seed in large quantities every 3-8 years making seed collection difficult and subject to finds of opportunity. The cones were dried, seeds removed and de-winged manually, heavier seed were removed from debris and cleaned via aspiration. A subset was weighed and counted to yield mean seed mass and 200 seeds were exposed to radiographic imaging to estimate the percent of filled and potentially viable seed.
Across all 130 families seed mass ranged from 1.0 to 4.4 mg and averaged 2.6 mg per seed. Seed mass and germination rate increased with elevation across all families and the relationship was strongest in trees in close geographic proximity from different elevations. Percent filled seed generally increased with elevation, but declined at the highest elevations. Surprisingly, estimated percent filled seed did not relate to germination rate. Germination experiments are ongoing to assess whether all families have optimal germination at standard conditions for the genus Picea (30C/8hr/light and 20C/16hr/dark). Seedlings are currently being propagated for phenotypic and physiological comparisons (growth, photosynthetic capacity, WUE, bud break, bud set) and will be out planted for continued study. Key findings are that red spruce in the southern Appalachians are producing the largest, most viable seeds the very tops of the mountains and have essentially run out of elevation to migrate towards. We hope to identify and deploy families that are suited to survive and regenerate at lower elevations and warmer conditions to resist losing species range for as long as possible in a warmer future.