Degrees of Alienation: Invasive Species Defined

From: Bill Cook, MSU Extension Forester/Biologist
Date: September, 2013

It’s important, for many reasons, to maintain the health of forests and other plant communities. Part of the definition of health is species composition.

Alien species displace native species and disrupt ecological processes. Alien species are also called non-native or exotic species. They are one of the greatest threats to regional forests.

Increasingly common, the term invasive is used, although invasive is more about behavior than nativity. Native species can also become invasive, when invasive is described as disruptive to natural systems.

Most alien species are not considered “bad”. Over 40,000 aliens have been introduced to North America. Honey bees are alien to North America. So are most of our food plants and animals. Apple trees are alien. Many common species in our environment were not here prior to European arrival. Most have had little negative impact to natural environments or have been beneficial to human beings. On the other hand, some species have grown to become significant problems.

Many damaging species are here to stay. A few will have (and have had) serious negative impacts. Some species will become naturalized with our native species. Other species can be eradicated, at least locally, or kept at more tolerable levels. Success stories exist, especially when new invasions are small.

Queen Anne's Lace
Queen Anne’s Lace
Many of the wildflowers that we appreciate in the summer are alien species that specialize in occupying disturbed sites, such as roadsides and old fields. Queen Anne’s lace, daisies, dandelion, most clovers, chicory, birds-foot trefoil, sow thistle, mullein, and tansies are not native to North America, but we see them frequently.

“Helpful” plants such as St. Johnswort and self-heal are aliens. Spotted knapweed and purple loosestrife have grown epidemic and very invasive. Buckthorn, garlic mustard, and autumn olive can prevent regeneration of forest species.

Removing well-established alien species from the landscape is quite difficult.

Alien species are not restricted to plants. The importance of alien and damaging insects and diseases is growing. Emerald ash borer, beech bark disease, oak wilt, and gypsy moth are a few better known and advertised examples.

Emerald Ash Borer
Emerald Ash Borer
Emerald ash borer, alone, has cost about 1.7 billion dollars and has changed the face of urban forests. Loss of black ash will convert many forested wetlands to open wetlands, which may be overcome with alien species. Beech bark disease will remove an important source of food for many northern forest species and an iconic tree from the forests. Oak wilt has killed many oak woodlands across Michigan and Wisconsin, and the disease is spreading.

Hemlock Wooly Adelgid
Hemlock Wooly Adelgid
On the horizon, we need to carefully watch for Asian long-horned beetle, hemlock woolly adelgids, and thousand cankers disease. Michigan State University has a new bulletin on these three species. Undoubtedly, the future will reveal additional threats. Vigilance is a key defense.

Why are alien species so bad? Again, most of them really aren’t. However, some of the problems caused by certain aliens include the loss of native species, decreased ecological stability, economic loss, reduced habitat quality, regeneration failure, and altered water and nutrient cycles. The threats are growing. Complicating and related factors involve smaller and smaller ownership size, human activities, climate change, and lack of management.

Learning more about these biological threats to forests and other plant communities can help in the battle to identify and eradicate, or control, these species. One source is the Michigan Invasive Plant Council. Another source is the Michigan Natural Features Inventory, which has a range of materials. Associate with local groups that work towards healthier plant communities.

One of the best tools available to managers and scientists is having thousands of citizen eyes watching for species that are out of place. Many new infestations are discovered by non-specialists. Early detection often leads to eradication. If you see something that seems out of the ordinary, be curious and find out what it is. Try contacting state agencies, conservation districts, Extension offices, conservation associations, and similar groups. Most of the time, the situation will be something normal. But you’ll never know until you ask.

Bill Cook, Forester & Biologist
MSU Extension, Upper Peninsula

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