The high rate of anthropogenic climate change projected for coming decades and evidence of low migration ability for many species have led researchers to warn of a looming extinction crisis. This threat is expected to be most acute for small-ranged endemic species, which could see novel climatic conditions develop rapidly across the entirety of their limited geographic ranges. To avoid extinctions, some conservationists have proposed that climate-imperiled species might be candidates for “assisted colonization” or “managed relocation” to new regions, outside their historical ranges. One major concern related to managed relocation is the possibility that some relocated species could later become problematic invasives where they are introduced. In this review, we consider how these emerging conservation challenges might unfold for the flora of New England. A range of evidence suggests that most plant species native to New England might be resilient to immediate extinction risk from climate change, as these species typically have broad geographic ranges and have migrated long distances in response to past climate change. In contrast, regions to the south, particularly hotspots of plant endemism in the southeastern US, harbor numerous small-ranged species whose current climatic niches could rapidly shift beyond their native ranges, leaving them vulnerable to extinction unless they colonize new regions to the north. Consequently, debates surrounding managed relocation in New England are likely to be focused primarily on the ecological risks versus conservation benefits of accepting climate-threatened endemic plant species from the southeastern US, and to hinge on concerns about the invasive potential of these species. To provide an empirically-grounded estimate of invasion risk from the introduction of US native plant species to New England, we reviewed invasive species lists for New England and tallied those species that are native to other parts of the contiguous US (versus other regions and continents). Between four and ten “invasive” or “potentially invasive” plant species reported from New England are from other regions of the contiguous US, depending in part on how issues of native versus exotic genotypes within taxa are resolved. A review of current floristic data from New England shows that these 4–10 problematic species are drawn from a larger pool of ∼374 US native plant species reported as exotic in the region, suggesting that only 1.1–2.7% of species appearing spontaneously as adventives in the region are viewed as invasive. In light of this analysis, we suggest that managed relocation is not likely to spawn large numbers of new invasives, and might therefore be judiciously evaluated alongside other conservation options for climate-threatened plant species. We propose a collaborative effort among field botanists, land managers, conservationists, and academics in New England, partnering with botanists in the southeastern US, to initiate fundamental research to experimentally test the viability and ecological effects of climate-threatened endemic plant species from the southeastern US in the New England region.

We conducted 12 days of field surveys on five mountains over 1100 m in elevation (Katahdin, North Brother, South Brother, Mount Coe, and The Owl) in Baxter State Park (BSP), Maine during the summers of 2013–14. In addition, we examined historic manuscripts, unpublished data, and herbarium records for plant records from the five mountains. Katahdin, the largest and tallest of the five mountains, has a rich history of botanical exploration and we documented 1559 herbarium vouchers that were collected from the mountain, primarily before the mid-1900s. Combining all data sources, we documented 38 families, 87 genera, and 131 taxa of vascular plants growing on our five study mountains above 1100 m in elevation from the 1800s to the present. This includes 28 taxa historically documented in the study area but not observed since 1980 at over 1100 m. In our study area, we found 16 taxa listed as endangered in Maine, 16 taxa listed as threatened, 10 taxa listed as of special concern, and five taxa considered possibly extirpated. This work provides a reference for future monitoring and plant conservation efforts within BSP and alpine habitats in Maine.

The Stephen West Williams Herbarium, an important early collection of plants from western Massachusetts, is in the Henry N. Flynt Library of Historic Deerfield. Most of the plants in the herbarium were collected between 1816 and 1818 in Deerfield, Franklin County, Massachusetts. The herbarium had apparently never been systematically examined by contemporary botanists prior to our work. The 390-page herbarium contains 556 specimens representing 453 species, 74% of which are native and 26% introduced. Eight of the native species in the herbarium are now considered rare in Massachusetts. Reflecting Williams' interest, about half the specimens in the collection had a medicinal use. Intensive floristic surveys in Deerfield between 1944 and 2015 failed to find 64 (14%) of the species collected by Williams, including about 4% of the native and 42% of the introduced species. The specimens establish a pre-1820 date for the presence of at least 90 introduced species that are currently considered naturalized in Massachusetts. The collection also provides documentation for 34% of the vascular plants in Edward Hitchcock's 1829 “Catalog of Plants Growing without Cultivation in the Vicinity of Amherst College,” the first flora for the Connecticut River Valley of Massachusetts.

Lily leaf spot disease, caused by the fungal phytopathogen, Pseudocercosporella inconspicua, infects Lilium canadense and L. grayi. The disease is currently ubiquitous in populations throughout the range of L. grayi. To determine the historical prevalence of the disease, lily specimens from eight herbaria were examined visually and microscopically, and a search for records of the pathogen was conducted using mycology databases and relevant literature. Of 516 herbarium specimens, two L. canadense and one L. grayi had the characteristic leaf lesions that contained diagnostic conidia of P. inconspicua. All three diseased specimens were collected prior to 1950. Mycological collections included two North American records of P. inconspicua on L. canadense, two on L. michiganense, one on L. philadelphicum var. andinum, and one on a cultivated Eurasian lily hybrid. Interestingly, the earliest diseased herbarium specimens were from the northeastern US with a later appearance in the southern Appalachians, a pattern also present in mycological collections of P. inconspicua. The rarity of historical specimens with disease, the temporal geographic pattern of occurrence, and the ubiquity of P. inconspicua in current populations of L. grayi suggest the spread of lily leaf spot disease in North America may threaten the viability of native Lilium host species.