Ecological costs of invasive species management create narrow safe operating spaces for aquatic plant communities

Aquatic plant communities exemplify the challenges associated with invasive species control. Chemical treatment with herbicides is the most common form of control strategy for aquatic invasive plants. However, aquatic herbicides can rapidly diffuse throughout the waterbody causing unintended consequences for non-target native species. Here we present analyses aimed at defining which conditions can maximize the success of Eurasian watermilfoil ( Myriophyllum spicatum ) control efforts while minimizing negative impacts to native aquatic plants. Using aquatic plant surveys conducted before and after chemical treatment in 474 lakes across Wisconsin, USA, we quantified the effects of chemical treatment on aquatic plants and predictors of management success. We found that chemical treatments rarely control Eurasian watermilfoil across lakes. Indeed, treatment generally appeared to compound the impacts of invasion on native plants across lakes, further reducing native richness and abundance and increasing unevenness in community composition. Only treatments applied to the whole lake and conducted soon after invasion effectively reduced invader abundance. Whole-lake herbicide applications were also those most likely to detrimentally affect native aquatic plant communities. As a result, the combination of treatment conditions and environmental factors that maximize treatment success and minimize inadvertent risks is rare. Our results can be used to refine aquatic plant management and permit decisions in North American lakes. More broadly, this work sheds light on resiliency in aquatic plant communities and potential ecological mechanisms driving success and failure in invasive species control.