By Doreen Pfost
Madison Magazine
Special To Channel 3000

Signs of an alien invasion will soon crop up throughout Dane County. Small purple heads will peek above tall roadside grasses and in open fields. Other intruders -- spindly, green and waist-high to a human -- will lurk in the semi-shade near bike trails.

Should we prepare to be overrun by visitors from another galaxy? No, although many landowners and resource managers might say they could more easily cope with little green men than with the challenge they actually face: fighting infestations of exotic plants.

Exotic, or non-native, plants exist in thousands of forms across North America. Most live harmlessly in gardens and yards, but some species, removed from their natural environments and the forces that kept them in check, become robust and aggressive. By monopolizing nutrients, sunlight and soil, invasive aliens overpower the plants native to our woodlands, prairies and wetlands and can dominate a landscape within a few years. On private property, uncontrolled outbreaks of exotics can give years-long headaches to landowners.

Who let these guys in, anyway?

Many invasive plants arrived in Wisconsin with the early settlers. Some were intentionally imported from Eurasia for specific purposes: as ornamentals (tartarian honeysuckle, for example), for erosion-fighting groundcover and windbreaks (crown vetch and multiflora rose), or to feed livestock (reed canary grass). Other invaders were stowaways, in ballast water, or with animals and feed brought by immigrants.

So, why were we not swarmed by these plants a century ago? For a number of possible reasons. Kelly Kearns, plant conservation program manager in the DNR's Bureau of Endangered Resources, says, "With most species, there's a lag between the time they're introduced and the time the population explodes." That suggests a period of adaptation in which plants become better able to compete in their new environment.

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