The landscape context of plant invasions in Mississippi wetlands

Invasive species are a known and growing threat to native ecosystems and the services they provide, and it is widely accepted that human activities contribute substantially to their spread. In a study of fifty-two north Mississippi wetlands, approximately 10% of the vascular plant species encountered were non-native, and 60% of the wetlands surveyed contained at least one plant species considered to be highly invasive. Furthermore, when highly invasive species were encountered, they were distributed across as much as 80% of the wetland area. Other work has shown that the degree of invasibility of a diversity of Mississippi wetlands was found to be much more strongly correlated with surrounding land use patterns than with the natural degree of connectivity among wetlands. For these reasons, we investigated the relationship of landscape features with exotic species richness in fifty-two freshwater wetlands across north Mississippi. Within those wetlands, invasibility was correlated only with certain forms of surrounding land cover, and inconsistently so. Agricultural land use appeared to enhance invasion of non-native plants, whereas density of surrounding wetlands and pine forest were correlated negatively with invasion. When wetland watersheds were classified based on the dominant land use as indicated by geospatial land cover data, no relationship was detected between dominant land use and degree of invasion. Indices of human activity surrounding the wetlands at the time of our vegetation surveys, however, did correlate closely with richness of exotic species, supporting the widely held notion that human alteration of the landscape can aid in the dispersal and establishment of non-native, weedy species.