Environmental Drivers of Plant Invasion in Wetland Mitigation

Abstract

Invasive plant species can alter natural communities and degrade ecosystem function, yet the factors influencing species invasion are poorly understood. The purpose of this study was to characterize environmental drivers of plant community structure and invasive plant prevalence within invaded portions of wetland mitigation sites. We sampled vegetation and environmental variables (prevalence index, light availability, soil physiochemistry, site age) across invasion gradients within and adjacent to invasive plant populations at multiple wetland mitigation sites in the Coastal Plain and Piedmont physiographic provinces of Virginia (USA). Data analyses involved a multi-metric statistical approach combining correlation and CCA to arrive at a plausible model for drivers of plant community structure in the context of invasive species prevalence based on environmental correlates. We targeted populations of Arthraxon hispidus (joint-head grass), Microstegium vimineum (Japanese stiltgrass), and Typha spp. (cattail), three invasive species that are known to be problematic on wetland mitigation sites in the region. Our analyses revealed specific environmental drivers of plant community structure and invasive species prevalence associated with populations of each invader, and a few factors consistently emerged as important drivers across populations of all targeted invaders – notably, canopy cover (light availability), prevalence index (representing frequency and duration of inundation and shallow soil saturation), and a handful of physiochemical variables. The results of this research have been used to develop a suite of recommended best practices that can be implemented at the outset of a wetland mitigation project to encourage desirable wetland plant communities and reduce the risk of invasion.