Factors restricting the spread of invasive plants at high latitudes

Prof Peter M. Kotanen1

1University Of Toronto, Mississauga, Canada

Invasions at high latitudes are an emerging problem. Few invasive plants currently occur in subarctic or arctic Canada, but northern towns may play a crucial role in future climate-driven range expansions by acting as centres for the initial arrival and establishment of invaders already present in southern areas. For instance, Churchill, Manitoba, on Hudson Bay, is exceptional in that more than 100 non-native plants have been locally recorded, reflecting this town’s history as a trading post, grain port, and tourist destination; 20-30 are well-established and persistent, as documented by a series of botanical surveys. Nonetheless, very few have spread from the townsite, and few have persisted in formerly occupied areas such as an abandoned military base and a former scientific rocket range. Propagule pressure likely contributes to this distribution; however, many of these invaders can set seed once established. Disturbance seems an inadequate explanation: outside of town, highly disturbed trails and roadsides host few invaders. Preliminary evidence suggests levels of herbivore damage are too low to influence distributions. Other research has suggested invaders often inhabit nutrient-enriched sites, but direct evidence is weak. Finally, invaders often may occur in warmer microsites; ongoing research will attempt to confirm this pattern. Understanding factors restricting invaders to populated areas may help to predict future risks; in particular, if temperature is directly limiting, rapid regional climate change may soon allow these species to spread to currently native-dominated sites.


I study interactions between plants and their natural enemies (herbivores and pathogens). Recent work has focussed on invasive plants and factors affecting variation in the herbivory and soil feedback they experience in their invaded range. For instance, my lab has documented striking latitudinal trends in damage to invaders such as the thistle Cirsium arvense and common burdock, Arctium minus, in their Canadian range: damage rapidly declines approaching the northern limits of these species. As a result, northern populations may face very different biotic environments than southern populations. I also have worked for many years on interactions between arctic-nesting geese and their food plants.

Professor: Department of Ecology and Evolutionary Biology, University of Toronto

Ph.D. (Ecology): University of California, Berkeley, Department of Zoology, 1994

M.Sc. (Ecology): University of Toronto, Department of Botany, 1987

B.Sc. (Botany and Zoology): University of Toronto, 1985

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