Relationship between the abundance ofLythrum salicaria (purple loosestrife) and plant species richness along the Bar River, Canada

Abstract

Lythrum salicaria (purple loosestrife) is a perennial herbaceous plant that was introduced in the 1800s into North America. Its geographical expansion has generated much concern. in part because its spread may lead to a reduction in the diversity of plant species in wetlands. We tested this hypothesis by examining the association between the abundance ofLythrum salicaria and vascular plant species richness in forty-one 2m × 2m plots located along the Bar River, Ontario, Canada. No significant differences in mean species richness were found between plots with and withoutL. salicaria. For those plots containingL. salicaria, species richness was not related to the percentage cover ofL. salicaria. Furthermore, there were no significant differences in the number of introduced plant species between plots with and withoutL. salicaria, nor were there differences with increasing percent cover ofL. salicaria. Plant species such asNuphar variegatum. Scirpus atrovirens, Scirpus cyperinus, andScirpus microcarpus were more likely to be found in plots withLythrum salicaria than without. However, no plant species were significantly more likely to be found in plots withoutLythrum salicaria than with it. Collectively, these results provide no support for the hypothesis that the number of species in wetlands is decreasing in association with the invasion ofLythrum salicaria in Ontario.