Current Events
Dr. Gretel Clarke
Dept. of Biological Sciences
Smith College
Northampton, MA
"Invasiveness of intra- versus inter-continental exotic plants in New England: Implications for assisted migration"
Mark your calendar for the next NEBC Meeting on June 1, 2018, at , with lecture by Dr. Gretel Clarke.
Abstract: Nearly half of the New England flora is not native to the region (45%, 1571/3534 species). Of exotic plant species, 74% are from other continents, a.k.a. 'inter-continental exotics', while 26% are from elsewhere in North America, a.k.a. 'intra-continental exotics'. We compiled New England state invasive species lists to assess the proportion of naturalized or adventive non-native species considered problematic, and tallied herbarium records to obtain a more direct assessment of spread/extent across the region. Inter-continental exotics were classified as invasive at four times the rate of intra-continental exotics (6% vs 1.5% of species). Our estimates using the number of naturalized/adventive species as the potential species pool for both groups makes this the best case-study to date comparing intra- and inter-continental exotic invasiveness for the flora of North America. Intra-continental exotic plants in New England come from elsewhere in the Eastern US (123 species), the Western US (76), or have native ranges spanning the 100th meridian (174). Inter-continental exotics most often hail from Europe and Asia, invasiveness being highest among species from Asia (5.7 vs 8.5% of species). Inter-continental exotics may be more invasive than intra-continental exotics because, for example, the former may more successfully escape natural enemies in New England, or may have evolved stronger competitive abilities on account of originating in floristically-diverse source regions (e.g., East Asia). Additionally, rates of invasiveness among intra-continental exotics may be lower since most plant species prone to rapid spread and increase in North America may have already done so in the distant past and are already part of our native flora. Thus, the remaining pool of North American plant species outside New England may be depleted of potential invaders. These results help gauge risks from "assisted colonization", as one of the major concerns with this controversial conservation approach relates to the risk of invasiveness of species translocated to new regions to keep pace with climate change. Since this approach would typically involve moving species modest distances within, rather than between, continents, it might be less risky than often presumed. However, our results also suggested risks may be elevated for legumes and aquatic plants.
