Invasive species often lack natural predators and diseases which control populations in their native environments. As the diversity and populations of native plants decrease, so does the variety of habitats available for wildlife. Exotics are primarily European and Asian species that have been intentionally or accidentally introduced to North America. Translocated species are native North American species whose pre-settlement range either did not include Wisconsin, or did not include certain areas of Wisconsin in which they are now a problem. Opportunistic species are native colonizers which can dominate certain natural communities and decrease species diversity.
Disturbance creates conditions that allow opportunistic species to invade the area.
In a healthy ecosystem, natural disturbances such as fire and flooding generally keep exotic and translocated species populations in check, allowing disturbance-adapted native species to thrive. With this in mind, a manager's short term goal should be to control the problem species, and in the long term to restore the natural processes of the ecosystem. Much of the control work being done is experimental, and often little data is collected. Because environmental and other conditions are variable over time and space, what works in one situation might not in another. This manual provides a range of techniques that have been reported to work in some situations.