Improving methods to evaluate the impacts of plant invasions: lessons from 40 years of research

Here the authors review the research methods used to measure the ecological effects of non-native plant invasions. In their synthesis they find that although the number of studies on invasion impacts has increased markedly in recent years, there is a lack of experimental studies, a bias among invader functional groups, and relatively few studies on ecosystem effects of invasions. They recommend utilization of longer-term studies that combine broad-scale observations, experimental manipulations, and predictive modelling across diverse invader functional groups and affected ecosystems to provide more comprehensive insight into the impacts of plant invasions. Abstract Methods used to evaluate the ecological impacts of biological invasions vary widely from broad-scale observational studies to removal experiments in invaded communities and experimental additions in common gardens and greenhouses. Different methods provide information at diverse spatial and temporal scales with varying levels of reliability. Thus, here we provide a synthetic and critical review of the methods used to evaluate the impacts of plant invasions and provide recommendations for future research. We review the types of methods available and report patterns in methods used, including the duration and spatial scale of studies and plant functional groups examined, from 410 peer-reviewed papers published between 1971 and 2011. We found that there has been a marked increase in papers published on plant invasion impacts since 2003 and that more than half of all studies employed observational methods while