Assessing vulnerability and resistance to plant invasions: a native community perspective

Abstract Risk assessments of biological invasions rarely account for native species performance and community features, but the assessment presented here could provide additional insights for management aimed at decreasing vulnerability or increasing resistance of a plant community to invasions. To gather information on the drivers of native plant communities' vulnerability and resistance to invasion, we conducted a literature search and meta-analysis. Using the data we collected, we compared native and invasive plant performance between sites with high and low levels of invasion. We then investigated conditions under which native performance increased, decreased, or did not change with respect to invasive plants. We analyzed data from 214 publications summing to 506 observations. There were six main drivers of vulnerability to invasion: disturbance, decrease in resources, increase in resources, lack of biotic resistance, lack of natural enemies, and differences in propagule availability between native and invasive species. The two mechanisms of vulnerability to invasion associated with a strong decline in native plant performance were propagule availability and lack of biotic resistance. Native plants marginally benefited from enemy release and from decreases in resources, while invasive plants strongly benefited from both increased resources and lack of enemies. Fluctuation of resources, decreases and increases, were strongly associated with higher invasive performance, while native plants varied in their responses. These differences were particularly strong in instances of decreasing water or nutrients and of increasing light and nutrients. We found overall neutral to positive responses of native plant communities to disturbance, but natives were outperformed by invasive species when disturbance was caused by human activities. We identified ecosystem features associated with both vulnerability and resistance to invasion, then used our results to inform management aimed at protecting the native community.