The genetic diversity of disjunct populations of Eastern hemlock (Tsuga canadensis) in Minnesota

Abstract

Tree conservation efforts have increasingly focused on intraspecific genetic diversity to help identify trees and populations for conservation. Disjunct populations and populations on the periphery of a species' range may be useful genetic resources. Eastern hemlock (Tsuga canadensis (L.) Carriere), a common native conifer in the eastern United States, exists on the northwestern edge of its range in Minnesota. Eastern hemlock has occurred in Minnesota in smaller disjunct populations for at least 1,200 years, but is now listed in the state as an endangered species. The number of trees has decreased significantly from over 5,000 in the early 1900s to less than 40 known mature trees, which are restricted to native stands in the northeastern region of the state. This decrease was due to logging, fire, herbivorous predation, and poor regeneration. There are additional trees of native provenance cultivated at the Minnesota Landscape Arboretum in Chanhassen, MN and trees of unknown provenance at various municipal and state parks and on private property across the state. We are using previously described microsatellite markers derived from Tsuga canadensis and T. caroliniana to investigate the genetic diversity of native disjunct populations and naturalized and cultivated trees in Minnesota. We collected foliage samples for DNA extraction from native provenance trees, trees of unknown provenance in naturalized and cultivated areas in Minnesota, trees in the Great Lakes region and trees from the center of species diversity in North Carolina. Additionally, over the course of two years we collected seed and grew seedlings from six native trees in Minnesota, four trees of native provenance from the Minnesota Landscape Arboretum, and 12 trees of unknown provenance. We are using these genetic resources to infer the relationships within and among populations and to unearth the origin of trees of unknown provenance. Results from this research can be used to understand the population genetics of Eastern hemlock in Minnesota and to inform decisions about the conservation and management of remaining native and cultivated trees.