Exotics or invasive non-native species is a reference to plants or animals that are not native to the area of interest. In a real sense, these species are "out of place," when they are introduced into a location where they didn't naturally evolve.
Exotics represent a threat to the ecosystem because they can displace native plants and animals. Many introduced species are aggressive and spread quickly with no natural pests or predators to keep their populations in check. Without these natural constraints, exotic species can out-compete natives allowing them to dominate the landscape, compromising the richness and health of the ecosystem.
A goal of a larger restoration effort at Mud Lake in St. Paul, was to control the exotic plant purple loosestrife. Purple loosestrife had been taking over their native plantings and the shorelines of their lake (top photo). Instead of spraying the loosestrife with herbicide which would also kill the native plantings, a biological control approach was adopted. Beetles that feed specifically on purple loosestrife were released in 1997 and the loosestrife was in check by 1999. The dramatic results over a two-year period are obvious in the project photos above.
For specific control recommendations, see the Invasive Non-native Plant Section.