Secondary invasion: The bane of weed management – identifying and overcoming the gap

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Dean Pearson

Publication Date:

Exotic plant invasions present a global threat to natural ecosystems, yet successfully mitigating this threat remains a challenge.  An implicit assumption in weed management has been that killing target invasive weeds addresses this problem.  However, studies increasingly demonstrate that a common response to killing a dominant target weed is secondary invasion – an increase in abundance of non-target exotics following target invader suppression.  We present results from a global literature review and meta-analysis quantifying the magnitude of the secondary invasion problem and identifying possible causes.  Of 168 studies examining the efficacy of exotic plant management in terrestrial habitats, only 29% quantified community responses sufficiently to evaluate secondary invasion.  Meta-analysis of 60 cases from 38 studies showed that control efforts strongly reduced target invader abundance overall, but the system responses tended toward increases in secondary invaders more than native plants. Importantly, 89% of the secondary invaders identified were classified as noxious or invasive plants.  Available information suggests that control method may sometimes favor secondary invasion due to side effects of management tools, such as when the use of broadleaf herbicides to target invasive forbs facilitates invasive grasses. However, secondary invasion is most strongly linked to reductions in the target invader’s abundance, suggesting that other invaders simply outcompete native plants in recolonizing following target weed suppression. These results demonstrate that we are becoming more effective at controlling target invaders.  However, suppressing a dominant invader does not necessarily restore plant communities. We discuss current strategies for mitigating secondary invasion and future research needs.

Resource Type:
Audio/Video, Conference Presentation, SER2019

Pre-approved for CECs under SER's CERP program

Society for Ecological Restoration