Managing multi-species plant invasions when interactions influence their impact

Invasions by multiple non-native plant species are common, but management programs often prioritize control of individual species that are expected to have the highest impacts. Multi-species invasions could have larger or smaller impacts than single-species invasions depending on how multiple co-occurring invaders interact to alter their abundance or per capita impacts. Synergistic interactions, such as facilitation, may lead to greater combined impacts. However, if management focuses on a single invader, suppressive interactions could produce unintended consequences, such as the release of a co-occurring invader with a stronger impact. The mechanisms described here highlight where better evidence is needed to predict the combined impacts of co-occurring invaders and which mitigation strategies are most effective. Focused research is required to provide such evidence, which can aid managers in prioritizing which plant invaders to target and in determining the best sequence of invader removal – one that minimizes detrimental impacts on communities and ecosystems.