|Maxwell, Bruce - MONTANA STATE UNIVERSITY|
|Fay, Peter - MONTANA STATE UNIVERSITY|
|Weaver, Theodore - MONTANA STATE UNIVERSITY|
Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 6, 2008
Publication Date: January 3, 2009
Citation: Rinella, M.J., Maxwell, B.D., Fay, P.K., Weaver, T., Sheley, R.L. 2009. Control Effort Exacerbates Invasive Species Problem. Ecological Applications 19(1):155-162. Interpretive Summary: There is great interest in controlling invasive species, mostly because they threaten native biota. Unfortunately, it is often impossible to control invaders without damaging natives to some extent. Our 17-year dataset shows this collateral damage can have lasting consequences. We sprayed a notorious grassland invader [leafy spurge (Euphorbia esula)] with herbicide. Herbicide temporarily suppressed E. esula, but it ultimately recovered and probably became more abundant due to spraying. The site’s other four exotic species responded similarly to E. esula. Alternatively, several natives had quite different responses to herbicide; four became locally extinct if grazing was excluded and two became very rare or locally extinct regardless of grazing. No management can be preferable when active management will have side-effects on native species.
Technical Abstract: Exotic invasive species are depleting the World’s native biota. Managers face a difficult dilemma after exotic species invade. They can use aggressive practices to reduce invader abundances, thereby reducing invaders’ competitive impacts on native species. But it is often difficult or impossible for managers to control invaders without collaterally damaging native species to some extent. So a critical question managers face is: which will be worse for native biota, invaders or things done to control them? We attempted to answer this question for a very common invasive species scenario. Specifically, we studied several grassland natives that had been coexisting with an invader for several decades and asked if collaterally damaging management (herbicide use) altered this picture of long-term coexistence. Our 17-year study showed one-time herbicide use quasi-permanently rarified some natives, drove some natives locally extinct when cattle-grazing was excluded, and likely increased invader abundances over time. Throughout the World, terrestrial and aquatic ecosystems are receiving herbicide applications for exotic species control. Some of the applications are doubtless warranted. For instance, small-scale applications can be effective for preventing spread of newly colonizing invader populations, and large-scale applications can increase wildlife or livestock forage in heavily invaded areas where virtually no natives remain. However, many other herbicide applications occur where substantial native populations occur, and our data suggest these applications can be ill-advised. Our cautionary tale emerged from an herbicide-treated grassland, but the allegory retains relevance in moving to any ecosystem where invasive species management collaterally damages native species.