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Eastern hemlock (Tsuga canadensis [L.] Carr.) is a widespread and ecologically important conifer species of eastern North America that is threatened by the hemlock woolly adelgid (Adelges tsugae Annand), a pest introduced into the United States from Asia in the 1920s. Information about the genetic composition of eastern hemlock is necessary to guide ex situ conservation efforts in the southeastern United States, where the species is expected to harbor relatively high amounts of genetic variation in areas of Pleistocene glacial refuge. Nineteen allozyme markers were used to quantify the genetic variation present in 20 eastern hemlock populations in the southeastern United States. Results indicate that the species has low levels of genetic diversity in the region compared to most other conifers, but greater population differentiation (F ST = 0.126). Populations along the eastern periphery and in the Appalachian interior exhibited higher levels of diversity than those along the western periphery of its geographic range. The results suggest that the glacial refuge area for eastern hemlock was likely located east of the southern Appalachian Mountains, and indicate that ex situ conservation seed collections should be concentrated in these areas of higher diversity.

Abstract Abstract Reforestation and restoration efforts have traditionally relied on “local” seed sources as planting stock. The term “local” has different meanings in different locales, since no single set of seed-collection zones has yet been widely adopted across the eastern United States. Given concerns about mitigating the effects of climate change, forest managers are increasingly seeking to move seed sources in a process called assisted migration, which would be facilitated if a common set of seed-collection zones were available. We developed a map of 245 seed-collection zones for 37 states by combining two ecologically important layers: plant hardiness zones and ecoregions. These new seed-collection zones should be used by seed collectors and nurseries to describe the origin of seed for plants and trees in the eastern United States. Common garden studies remain the gold standard for determining how far to move seed from any particular seed-collection zone. For species that have not been field-tested, seed movement that is limited either within a seed-collection zone or between adjacent seed-collection zones is a reasonable general guideline.

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Current guidance on sourcing native plants to support ecosystem function focuses on the high risk of failure when unsuitable material is used in ecological restoration. However, there is growing recognition that risks may be lower and rewards higher at highly disturbed sites isolated from remnant populations, especially when considering support for pollinators, wildlife, and other ecosystem functions. We developed the first decision support tool using expert opinion to assess suitability of different native plant sources, including horticultural cultivars, in two different planting contexts. We assessed the suitability of 761 sources for 72 commonly sold native species in two different planting contexts (small, isolated, highly disturbed sites vs. large, undisturbed sites near remnant populations). Information on genetic and adaptive backgrounds of sources was strikingly lacking, forcing us to exclude one-third of sources from our assessment. While only 3% of cultivars received high suitability scores for use in large, undisturbed sites near remnant populations, 52% received high suitability scores in small, isolated, highly disturbed sites. However, nearly 25% of cultivars had floral or leaf traits that differed from wild plants in ways that may compromise their ability to support pollinators and other wildlife. Forbs and cultivars lacking genetic diversity and source information were most likely to have altered traits. We recommend that native plant breeders and sellers work together to ensure ecosystem function, adaptation, and diversity information is available to consumers, that consumers request this information to drive demand, and that researchers further investigate how context influences risks and benefits of different sources. Implications for Practice• Most native plant sources available in the marketplace are cultivars that are typically unsuitable for ecological restoration efforts aimed at reestablishing diverse, self-sustaining populations. However, they may be appropriate in certain planting contexts, where the primary aim is to support pollinators, wildlife, and other ecosystem functions. Our structured decision-making tool is the first of its kind to allow users to assess benefits and risks of planting these sources in different contexts. • Information on adaptation, genetic diversity, and ecosystem function is lacking for a majority of native plant sources in the marketplace, particularly for cultivars. Native plant breeders and sellers should work together to ensure this information is available and consumers should ask for this information to help drive demand.Author contributions: EL, SJ completed the SDM tool and tested it with AK, KH, AN, TK; AW, AK created the dataset of source attributes; JZ analyzed and visualized the results; AK, AN, KH, DT, TK drafted and revised the manuscript; all coauthors edited the manuscript.