Climate warming and the arrival of potentially invasive species into boreal forest and tundra in the Hudson Bay Lowlands, Canada.

As the extremity of Arctic climate lessens with global warming, the risk of invasion increases. We assess the presence of introduced plant species and their persistence (since the previous survey) in a Canadian subpolar site on the Hudson Bay with a history of human introductions from large-scale grain inputs. Widespread sampling was done to locate all introduced plant species in the Churchill, MB, Canada area. We quantified edaphic variations through soil sampling, and the effect of aspect on introduced species’ richness, cover, and height. At the regional scale, species life history traits and climate envelopes (average and variability of climate in a native range) were established to determine if persistent plant species had similar climate requirements. We found that despite statistically significant warming and increased precipitation, the number of introduced plant species in sub-Arctic Churchill declined from 80 to 36 between the 1989 and 2013 sampling periods. We found that introduced species favor locally warmer, human-disturbed sites with above average soil nutrients. The plant species that remained in Churchill since the 1989 survey compared to those that did not persist are better able to tolerate colder temperatures and have wider, more variable climate envelopes. The decline in introduced species is likely linked to changes in grain shipment inputs. Many of the introduced species recorded in 1989 may have only existed through constant seed subsidies from imports, suggesting that most species have not yet been successful in the absence of human modification. Although the number of introduced plants has decreased, we suggest that continuous disturbance is no longer required for some introduced species to persist suggesting that a climate threshold may have been crossed for some species. One introduced species (Taraxacum officinale, common dandelion) has spread to areas that have not been modified by humans and is now growing in two undisturbed locations. Its current distribution outside disturbed areas does not yet warrant the distinction of invasive at this time. The findings of this study suggest that in the Canadian Arctic, if disturbance and nutrient enrichment are reduced, the potential for introduced plants to establish and possibly become invasive is still limited but will likely change as warming continues. [ABSTRACT FROM AUTHOR]