From the Source to the Outlet: understanding the Distribution of Invasive Knotweeds along a North American River

• Published in: River research and applications 2016-06, Vol.32 (5), p.958-966
• Main Authors: Duquette, M.-C., Compérot, A., Hayes, L. F., Pagola, C., Belzile, F., Dubé, J., Lavoie, C.
• Format: Article
• Language: English
• Subjects: Aquatic plants; bohemian knotweed; Distribution patterns; Environmental management; Fallopia japonica; Fallopia × bohemica; Freshwater; genetic diversity; Genotypes; Introduced plants; invasive plant; Japanese knotweed; Outlets; riparian corridor; Riparian vegetation; Rivers; Spatial distribution; Waterways
• ISSN: 1535-1459; 1535-1467
• DOI: 10.1002/rra.2914

Understanding the drivers of exotic plant invasions along waterways is crucial for helping environmental managers devise effective control strategies. We combined a field survey, molecular data and a logistic regression model to further our understanding of the spatial distribution of Japanese (Fallopia japonica) and Bohemian (Fallopia × bohemica) knotweeds along the entire course (185 km) of a river located in Québec (Canada). Both knotweeds were abundant along the river, but each had a distinct spatial distribution pattern. Only one genotype for each knotweed species or hybrid was found, suggesting that the individuals established along the Chaudière River resulted from the propagation of rhizome or stem fragments. The distance from the nearest town or village was the only explanatory variable significantly correlated to the spatial distribution of knotweeds. However, spatial autoregressive coefficients were significant, indicating that knotweeds were more likely to occur close to other knotweeds. In summary, the invasion was probably initiated by the introduction, in riverside towns and villages, of a few individuals of the same genotype. The clones then spread vegetatively, probably during spring floods. The rhizome and stem fragments spread over short distances, dispersing downstream from urban centres. The introduction of just two knotweed genotypes along the Chaudière River was sufficient to initiate a massive riverside colonization, as few riparian vegetation types were apparently able to resist knotweed invasion. Copyright © 2015 John Wiley & Sons, Ltd.