Exotic plant species of the St Lawrence River wetlands: a spatial and historical analysis

Publication Type:Journal Article
Year of Publication:2003
Authors:Lavoie, C, Jean, M, Delisle, F, Létourneau, G
Journal:Journal of Biogeography
Date Published:2003
ISBN Number:1365-2699
Keywords:Butomus umbellatus, Diversity, exotic species, Fringillidae, herbarium specimens, invasive species, Lythrum salicaria, Phalaris arundinacea, Phragmites australis, Serinus, Serinus canaria, St Lawrence River, wetlands
Abstract:Abstract Aim  To evaluate the importance (number of species, plant cover) of the exotic flora in seven well-defined sectors of one of the most important transportation waterways in North America. To determine the impact of exotic species on wetland plant diversity and reconstruct the spread of some invasive species. Location  St Lawrence River, southern Québec. Methods  The exotic flora (vascular plants) of wetlands bordering the St Lawrence River was studied using 713 sampling stations (25 m2) along a 560-km long corridor. Results  Exotic species represent 13.7% of the vascular flora of the St Lawrence wetlands. The relative plant cover occupied by exotic species is high in some of the fluvial sectors (42–44%), but low (6–10%) in the estuarine sectors. Wetlands (marshes) surrounding islands were particularly susceptible to invasion by exotic plants. Historical, abiotic and landscape factors may explain the differences observed between sites. Purple loosestrife (Lythrum salicaria L.) is the most common exotic species of the St Lawrence wetlands, but other species, namely flowering-rush (Butomus umbellatus L.) and reed canary grass (Phalaris arundinacea L.) are much more invasive. There is no linear relationship between the exotic species cover and the diversity of wetland plants; low diversity sites can be dominated by either exotic or native plant species. In the other sites, exotic species generally have little impact on plant communities and can contribute to increase diversity. Common reed (Phragmites australis (Cav.) Trin. ex Steudel) and reed canary grass, both considered as exotic species in this study, clearly have a stronger impact on plant diversity than flowering-rush and purple loosestrife. Main conclusions  This study shows that the global impact of an invader cannot be adequately evaluated with only a few highly invaded sites. While nationwide strategies have been developed to control exotic species, large surveys are essential to adapt them to regional particularities.
Short Title:Journal of Biogeography
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