Macro-scale assessment of demographic and environmental variation within genetically derived evolutionary lineages of eastern hemlock (Tsuga canadensis), an imperiled conifer of the eastern United States

Eastern hemlock (Tsuga canadensis) occupies a large swath of eastern North America and has historically undergone range expansion and contraction resulting in several genetically separate lineages. This conifer is currently experiencing mortality across most of its range following infestation of a non-native insect. With the goal of better understanding the current and future conservation potential of the species, we evaluate ecological differences among populations within these genetically defined clusters, which were previously inferred using nuclear microsatellite molecular markers from 58 eastern hemlock populations. We sub-divide these clusters into four genetic zones to differentiate putative north-central, north-east and southeast (SE) and southwest evolutionary lineages in eastern hemlock. We use demographic data (relative abundance, mortality, and seedling regeneration) from the Forest Inventory Analysis program in conjunction with environmental data to model how these lineages respond to current and future climatic gradients. Ecologically meaningful relationships are explored in the intraspecific context of hemlock abundance distribution and then related to genetic variation. We also assess hemlock’s colonization likelihood via a long distance dispersal model and explore its future genetic and ecological conservation potential by combining the future suitable habitats with colonization likelihoods. Results show that future habitats under climate change will markedly decline for eastern hemlock. The remaining areas with higher habitat quality and colonization potential are confined to the SE, the genetic zone nearest the species’ putative glacial refugia, pointing to the need to focus our conservation efforts on this ecologically and genetically important region.