trees Invasive Plant Resources

Understanding the Problem

What is an Invasive Plant?


The Invasive Plant Association of Wisconsin (IPAW) defines invasive plants as "non-indigenous species or strains that become established in natural plant communities and wild areas and displace native vegetation." The key point is that invasive plants (unlike less-troublesome weeds) out-compete the natives in forests, prairies, wetlands and other intact ecosystems. This often leads to a cascade of problems affecting tree regeneration, wildlife abundance, invertebrate diversity, rainwater runoff, and recreational values.

Non-indigenous species are also known as non-native, alien, or exotic. These terms, for purposes of this website, refer to species that did not occur in a specific area or plant community before European settlement of the upper Midwest.

Weeds, as we define them, are plants that grow primarily in disturbed areas. Most weeds do not invade and dominate natural areas, but tend to be confined to disturbed soil, edges, and degraded habitats or appear in small numbers. All invasives are also weeds, but of the hundreds of non-indigenous plants growing wild in every state, only a few dozen are seriously invasive.

Why are Invasives so Successful?

Invasive plants tend to have certain advantages over native plant species. These include some or all of the following:
  • Absence of the diseases, insects, and other plant-eating organisms that help keep populations in check in their geographic place of origin.
  • Ability to grow rapidly and leaf-out earlier than native plants, which gives the invader a competitive advantage in terms of capturing space, sunlight, soil moisture and nutrients - all essential components of healthy plant growth.
  • Capacity to reproduce and spread quickly and in great numbers, often from seed, underground roots and rhizomes, or other plant parts that remain viable in the ground for a long time.
  • Ability to thrive in a wide variety of habitats and soil conditions.
"The good news is that this is one environmental problem we can do something about. I have seen the tremendous difference even a few individuals can make in the battle to regain the land for native species."
    Elizabeth Czarapata, Invasive Plants of the Upper Midwest,

An Ounce of Prevention

One state's out-of-control invasive species may be nonexistent or only just getting a foothold in another state. Indeed, the presence/absence of an invasive may be true even on neighboring parcels of forest land - where one tract is free of a particular weed while the other is highly infested. Aim for prevention! Early detection and control efforts really pay off.

Credits: Some of the above was exerpted from Invasive Plants of the Upper Midwest, by Elizabeth Czarapata, University of Wisconsin Press, 2005.

USDA Forest Service - Forest Invasive Plant Resources
February 6, 2005