Assisted Migration
What can be done to preserve tree species at risk of extinction in the Northeast as the climate changes? One conservation strategy (although still largely hypothetical and debated) is attempting to answer that very question: assisted migration “proposes that some climate-threatened species might require direct human intervention in order to keep pace with climate change” or disappear entirely (Bellemare 25). By intentionally planting species in predicted suitable habitats outside the trees’ historically native ranges, humans could help those species migrate in the face of a rapidly changing climate altering their native habitats. A chorus of opposition, however, points to assisted migration as a potentially troublesome strategy. The scientific community and public worry that migrated plants could grow and reproduce rapidly in their new habitats, out competing native species just as other invasive species have done before. Take, for example, the opportunistic nature of black locust (Robinia pseudoacacia), which is native to the Appalachians and Ozarks. Planted in New England for erosion control and lumber, locust spreads aggressively through root suckering. It can increase soil nitrogen levels where soils were previously nitrogen-poor, threatening native plants used to those conditions (“Black Locust”). While locust is one example, researchers are investigating how much of a risk new species introduced outside of their native ranges actually present. Only 1 to 2% of US native plant species reported as adventive or naturalized in New England (~6 species out of 400) show up on the invasive species watch list for the region (Bellemare
This report recommends a list of climate-adapted tree species for riparian and floodplain forest restoration, informed by considerations of which tree species will thrive in the Deerfield River watershed in a future altered by climate change, yet more research is needed. At Acadia National Park in Maine, researchers are examining approximately 1,000 tree species to determine which might be able to survive in the park decades from now. Their efforts could help to inform the growing body of research on which trees specifically could benefit from assisted migration when they are limited by dispersal ability and slower growth rates than herbaceous plants (Ostrander). 28). Plants native to the US that are moved short distances in the context of assisted migration likely do not present the same threat as known invasive plants native to other countries, although more research is still needed (Bellemare). The trees of New England will be impacted by climate change, but when is assisted migration necessary? One way to assess the risk of extinction of a species is its dispersal ability (Thomas et al.). There is evidence to suggest that plants native to New England with more extensive geographic ranges might be less at risk of extinction in the face of climate change (Bellemare et al.). The more widespread a species range, the more likely that species has the capacity to migrate in the future, evidenced by its dispersal ability in the face of previous climate shifts (Bellemare et al.). Assisted migration may be a strategy better suited to endemic species with smaller geographic ranges that won’t be able to migrate to more suitable habitats in the face of a rapidly changing climate.
