Eastern hemlock (Tsuga canadensis (L.) Carrière) is a slow-growing and long-lived conifer in the Pinaceae family. Its range extends from Nova Scotia west into Wisconsin and Minnesota and south along the Appalachian Mountains, Northern Georgia, and Alabama with outlier populations along the western range limits in Minnesota, Ohio, Indiana, Georgia, Alabama, Kentucky, and Tennessee. Eastern hemlock is a foundation species across its range that has transformational effects on its surrounding ecosystem. As of 2013, eastern hemlock has been listed as near threatened due to the presence of an invasive insect, the hemlock woolly adelgid (Adelges tsugae Anaand.), which is destroying populations in the eastern United States. Eastern hemlock has historically existed in Minnesota in disjunct and marginal populations and it is listed as endangered in the state. Additionally, trees of known native provenance at the Minnesota Landscape Arboretum were collected from a now extirpated population near Mille Lacs Lake, Minnesota and there are additional trees of unknown provenance in state and municipal parks and public gardens. The objectives of this research were to understand the propagation potential and genetic diversity of native and unknown provenance eastern hemlock in Minnesota with the aim of using this information to inform conservation strategies. Field site visits revealed that there are less than 40 known native mature eastern hemlock trees in Minnesota, with scattered seedlings and saplings. Information on individual trees and herbarium specimens including details on height, diameter at breast height (DBH), location, and notes on tree health, are included in the supplementary spreadsheet Appendix B. Using previously published microsatellite markers (SSRs) derived from eastern hemlock, we observed inbreeding in disjunct Minnesota native trees when compared with trees in the main range. Hemlock Ravine was the most genetically distinct from all other sites sampled, as were native origin trees at the Minnesota Landscape Arboretum. Interestingly, neither of these two sites were similar to the other Minnesota disjunct site, West Duluth. The West Duluth trees were more genetically similar to populations sampled in Wisconsin and Michigan. Seedlings grown from native Minnesota trees also displayed inbreeding. From paternity analyses, we found that trees at the Minnesota Landscape Arboretum are potentially outcrossing with non-native trees. Additionally, trees in Minnesota of both native and non-native origin can be propagated successfully via seed. Trees at the Minnesota Landscape Arboretum in particular are amenable to seed propagation, but had little overall success when propagated vegetatively, with the exception of a singular accession (MLA19). These discoveries can be used to inform conservation practices in Minnesota. We recommend that land managers continue in situ preservation of sites across Minnesota and continue ex situ maintenance of eastern hemlock trees in parks and gardens. We also recommend that land managers focus on native Minnesota trees when sourcing material for propagation, planting, and seed-banking in national and local repositories.
University of Minnesota M.S. thesis.September 2017. Major: Applied Plant Sciences. Advisors: Stan Hokanson, James Bradeen. 1 computer file (PDF); 135 pages + 1 supplementary file.
The Genetic Diversity and Conservation Potential of Eastern Hemlock (Tsuga canadensis (L.) Carrière) in Minnesota.
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