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

Abstract

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.

To list or not to list: using time since invasion to refine impact assessment for an exotic plant proposed as noxious

“…In particular, negative local-scale relationships may reflect patterns of invasibility rather than invader impacts (Ortega and Pearson 2005, Stricker et al 2015, Pearson et al 2016. While observational data can be quickly gathered to identify negative relationships between invading and native species, interpretation of such patterns is limited by the correlational nature of the data.…”

“…Negative local-scale correlations between native and invader abundance are often used to identify apparent impacts of plant invaders in observational studies (Stricker et al 2015). Current approaches incorporate safeguards to help ensure that measured relationships are driven by invader impacts rather than confounding factors that might mimic impact.…”

“…One advantage of these studies is that they consider cumulative effects on native communities exerted over relatively long time scales whereas experimental approaches typically address only short-term responses (Stricker et al 2015, D'Antonio and Flory 2017, Tekiela and Barney 2017. However, it can be difficult to distinguish causes from effects of increased invader abundance; that is, negative local-scale relationships between invader and native abundance may reflect patterns of invasibility and/or invader impacts (Ortega and Pearson 2005, Stricker et al 2015, Pearson et al 2016. However, it can be difficult to distinguish causes from effects of increased invader abundance; that is, negative local-scale relationships between invader and native abundance may reflect patterns of invasibility and/or invader impacts (Ortega and Pearson 2005, Stricker et al 2015, Pearson et al 2016.…”

“…However, it can be difficult to distinguish causes from effects of increased invader abundance; that is, negative local-scale relationships between invader and native abundance may reflect patterns of invasibility and/or invader impacts (Ortega and Pearson 2005, Stricker et al 2015, Pearson et al 2016. Not surprisingly then, correlations between invader and native abundance are used to infer impact in some studies (reviews in Vil a et al 2011, Hulme et al 2013, Stricker et al 2015 and invasibility in others (Stohlgren et al 1999, Knight and Reich 2005, Mills et al 2012). Not surprisingly then, correlations between invader and native abundance are used to infer impact in some studies (reviews in Vil a et al 2011, Hulme et al 2013, Stricker et al 2015 and invasibility in others (Stohlgren et al 1999, Knight and Reich 2005, Mills et al 2012).…”

“…The magnitude of invader impacts should generally change over time as a function of invader abundance (Dost al et al 2013, Sofaer et al 2018; but see D'Antonio and Flory 2017). Time since invasion has seldom been considered in studies of plant invader impacts (Dost al et al 2013, Stricker et al 2015, D'Antonio and Flory 2017), yet such information could improve interpretation of local-scale patterns measured via observational methods. Such time-since-invasion data could be related to local-scale plant community data collected at time t to specifically test for temporal signatures consistent with invader impact.…”