Plant invasions are a serious issue but once the original invasive plant has been exterminate, a second problem typically arises in the form of secondary invasion. The U.S. Forest Service gives a global literature review and meta-analysis with the goal of quantifying the magnitude of the effects of these invasions as well as their causes.

Eighty-nine percent of these secondary invaders were classified as noxious/invasive plants:

Increases in secondary invaders were correlated with target invader reductions, but control method and target invader growth form failed to explain variation in secondary invader responses. These results suggest that target invader suppression is the key factor driving release of secondary invaders. However, management side effects, target invader legacy effects, provenance effects, and shifting environmental conditions may all facilitate secondary invasion.

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