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Invasive species reports and impacts have been increasing significantly, and will continue to be in the news. Conservation groups, agencies, and landowners are running to get on the control bandwagon, as indeed they should. However, a bit of clarity might be helpful and maybe even a bit of caution.

The idea of "invasiveness" is not always a single or simple concept. Additionally, lines between "good" and "bad" are not always clear. There are degrees of "invasiveness" as one might expect with any natural spectrum. Different habitats host different species, with different effects. Sorting through the numerous factors can sometimes lead to confusion and occasionally to errors in perception.

The impact of an invasive species on its environment, and the importance of the impacted system, can be difficult to evaluate. This should be the measure of "invasiveness", not simply taxonomy or nativity. For an example of a plant assessment tool, visit the Michigan Invasive Plant Council at [http://forestry.msu.edu/mipc].

An invasive species is essentially a population of a plant or animal that grows so disproportionately large that it causes ecological disruption of a host system. "Invasiveness" is generally an indicator of some kind of natural imbalance. Invasive species can be either exotic or native. Their impacts can vary with geography, environmental conditions, and other factors.

An exotic is merely a species that didn't evolve within a particular natural system and came from somewhere else. That "somewhere else" could be another part of Michigan, another part of the USA, or from a different continent. Some folks use the term "species out of place". A native is a species that naturally belongs to a particular natural system.

In terms of our northern forest ecosystems, examples of invasive exotics would be European buckthorn, glossy buckthorn, and garlic mustard. Invasive natives might include white-tailed deer, Pennsylvania sedge, and ironwood.

Common invasives affecting other ecosystems include such species as Eurasian water milfoil, zebra mussels, purple loosestrife, Asian ladybugs, and spotted knapweed. Aquatic systems host more newsworthy invasives than terrestrial systems. Forest systems may be less vulnerable, but that would be an opinion that could change quickly. Finding and controlling or eradicating invasive species can be very problematic.

A bit different from exotic invasive species, exotic pests directly attack native species. Examples include Dutch elm disease, emerald ash borer, beech bark disease, and white pine blister rust. There are over 400 exotic disease and insect pests that have impacted trees and woody plants in the United States. The frequency of new introductions is likely to increase, correlated with our trade volume with China and eastern Asia.

Despite increased ecological disruptions from these kinds of sources, it would be helpful to remember that exotic is not always bad. In fact, there are more beneficial exotic species than harmful ones.

Consider species such as ring-necked pheasants, honey bees, salmon in the Great Lakes, and turkeys in the Upper Peninsula. They are exotic species. There are also many domesticated species, such as cattle, wheat, horses, and scores of ornamentals. Cropland and pastures occupy huge amounts of acreage, filled with exotic species, yet most people would see this land use as a good thing. As for trees, many of our common residential trees are exotics and sometimes exotic species are ideally suited for tree plantations, such as European larch.

To be certain, we as a society and especially the minority who own land need to pay more attention to the role of exotic and invasive species. They represent one of the top threats to our forests, wetlands, lakes, and other natural systems. However, part of that learning process is to understand the context, background, and relative importance of particular species and their impacts. Nature has very few "one size fits all" descriptions.

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Bill Cook is an MSU Extension forester providing educational programming for the entire Upper Peninsula. His office is located at the MSU Upper Peninsula Tree Improvement Center near Escanaba. The Center is the headquarters for three MSU Forestry properties in the U.P., with a combined area of about 8,000 acres. He can be reached at cookwi@msu.edu or 906-786-1575.

Prepared by Bill Cook, Forester/Biologist, Michigan State University Extension, 6005 J Road, Escanaba, MI 49829
906-786-1575 (voice), 906-786-9370 (fax), e-mail: cookwi@msu.edu

Use / reprinting of these articles is encouraged. Please notify Bill Cook.
By-line should read "Bill Cook, MSU Extension" Please use the article trailer whenever possible.

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Last update of this page was 5 November, 2018