The spatiotemporal dynamics of plant invasions

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My research team has shown, over the last 20 years, that exotic plants of cold-temperate regions that are cold hardy and able to exploit a resource (habitat) like the road network will rapidly expand their populations and invade new regions. Nonetheless, their effects on biodiversity are context-dependent, and the extent of their impacts on the population dynamics of other plants or animals remains to be verified. The long-term objective of my research program is to understand why certain exotic plant species are more successful than others in establishing large populations. For the next 5 years, I have 4 short-term goals. (1) I propose to investigate the factors responsible for ornamental plant naturalization by studying historical gardens. By comparing the list of species planted in the gardens to those that naturalized in their vicinities, I expect to better understand processes associated with naturalization. I hypothesize that plant hardiness is an important explanatory factor, but that propagule pressure is equally important to naturalization success. (2) I also want to explore one of the main hypotheses of plant invasions (enemy release) from a historical (herbarium-based) perspective. I hypothesize that exotic species are exposed from the outset to herbivores/pathogens already present in the introduced range, but that the attacks increase with plant population expansion (larger food source or host abundance, long-term adaptation to a new food source). I believe that long-term herbivory/pathogen trends (impacts on plants) can be detected with herbarium specimens. (3) I want to determine whether roads act not only as corridors, but also as invasion foci for weeds, because the extent to which invaders expand their populations from transportation corridors to adjoining lands remains to be quantified. Although a road network probably structures the spatial distribution of invaders over a region, I hypothesize that habitat characteristics better explain population size of invaders near roads. (4) Finally, I propose to investigate the effects of two plant invaders (Reynoutria japonica RJ and Impatiens glandulifera IG) on ecosystem functions (erosion protection) in riparian ecosystems, to precisely evaluate whether these plants have an impact on river bank erosion. I hypothesize, contrary to general belief, that the effect of RJ on erosion is minor because of its extensive rhizomatous root system. On the other hand, I hypothesize that the impact of IG on erosion is major, especially in regions with ice movement in spring. This impact would be a consequence of the replacement of perennials by this annual, leaving banks totally devoid of vegetation in late fall. This research program will significantly contribute to the understanding of biological invasions and plant biogeography in Canada and other cold-temperate areas.