2018 ASHS Annual Conference

Eastern hemlock (Tsuga canadensis (L.) Carr), a common conifer in the eastern United States, exists on the northwestern extent of its native range in Minnesota. The species has always been rare in the state, possibly due to the cold, dry climate, but it has declined in the last century due to pressures from fire and logging. Eastern hemlock is currently considered to be the most endangered tree species in Minnesota, with less than 40 mature trees left in native stands in the northeastern region of the state. Additionally, there are trees of known native origin at the Minnesota Landscape Arboretum and trees of unknown, but possibly native origin at various municipal and state parks across the state. We used eight previously described microsatellite markers derived from Tsuga canadensis to investigate the genetic diversity and differentiation of disjunct native populations and cultivated trees in Minnesota and to determine the origin of cultivated trees of unknown provenance. We collected foliage samples for DNA extraction from all known native trees and select cultivated trees in Minnesota, trees in the Great Lakes region and trees from North Carolina, the center of species diversity. Additionally, over the course of two years we collected and grew seed from 17 Minnesota native trees and 4 trees of wild provenance from the Minnesota Landscape Arboretum. Considering only native adult trees, population differentiation and inbreeding as measured by Slatkin’s were relatively high (R_st = 0.123; R_IS = 0.219). Structure and Principal Component Analysis revealed Minnesota native populations to be genetically distinct from main range populations in Michigan and North Carolina. Paternity analysis of seedlings revealed few statistically significant mother-father pairs, although likely pollen parents often included non-native trees. Results from this research are being used to inform decisions about the conservation and management of existing native and cultivated trees. This includes using select native trees as seed sources for restoring populations and supplying the region’s landscape nursery industry with native sourced plant material. Although these disjunct populations are subject to potential genetic risks posed by inbreeding, they may prove useful as a source of genetic resources for problems such as the hemlock wooly adelgid (Adelges tsugae Anaand.) currently killing large numbers of trees in eastern U.S. populations.