Not All Roads Lead to Rome: A Meta-analysis of Invasive Plant Impact Methodology
Tekiela, D. R., & Barney, J. N. (2017). Not All Roads Lead to Rome: A Meta-analysis of Invasive Plant Impact Methodology. Invasive Plant Science and Management, 10(4), 304-312. PDF.
Summary
Several studies have assessed plant impacts using either observational (e.g., comparing invaded vs. uninvaded sites) or experimental (e.g., removing weeds and assessing invaded vs. removal sites) methodologies. Understanding impacts is critical for prioritizing monitoring and management for range-shifting species in the context of climate change. But, these two approaches (observational vs. experimental) might lead to different conclusions about the magnitude of impact. Therefore, Tekiela & Barney (2017) performed a meta-analysis of 174 studies of invasive plant impacts to test whether the two approaches differ in overall direction and magnitude of measured impact. When the studies were transformed to focus only on magnitude of change (removing directionality by taking the absolute value of the impact measurement), there was a significant impact of invasive plants on ecosystem properties and no difference between observational vs. experimental approach. Tekiela & Barney (2017) emphasize the importance of removing directionality. For example, some species might cause an increase in soil N, others might cause a decrease in soil N. Both are potentially important impacts, but the positive vs. negative directions would cancel each other out if compared directly. When all values are transformed to magnitude of change, the impacts of invaders are significant across study methodologies.
Take home points
There was no difference between impacts measured by observational vs. experimental approaches.
With longer time since invader removal, removal sites became more different from invaded sites. This suggests that many ecosystems need long recovery times, but can recover.
Management implications
Observational and experimental approaches are equally effective for assessing impacts.
Keywords
Range Expansion; Impact Study; Meta-analysis; Invasive Plant; Risk Assessment