Climate Change, Managed Relocation, and the Risk of Intra-Continental Plant Invasions: A Theoretical and Empirical Exploration Relative To the Flora of New England
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.