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The Monsters That Are Overrunning America

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Alien monsters are on the rampage, destroying everything in their path. We’ve all seen the stories. No, I’m not talking about science fiction and horror movies, I’m talking about invasive species: Asian carp and zebra muscles in the Great Lakes, pythons in the Everglades, starlings in the tree out back, kudzu in the Southeast, and honeysuckle here, there, and everywhere.

This post gives a little background on non-native invasive plants (NNIPs). The next post will look at the prevalence of NNIPs in Missouri forests.

NNIPs are plants that originated elsewhere and were brought here by humans. In their native range, they are kept in check by various factors – for instance, something eats them, growing conditions are not optimal, or other plants compete effectively with them. But brought to a different ecosystem, they spread out of control. One result is that they displace native species. Another is that other native plants and animals are often adapted to eat or use the species being displaced, but not the NNIPs. Thus, the other plants and animals become unable to survive, and they vanish, too. And finally, NNIPs are often of little economic value.

For instance, multiflora rose, an important NNIP, grows into impenetrable, thorny tangles that crowd out other plants and injure the flesh and eyes of animal species. It provides cover for birds, but so do the species it displaces. Its rose hips are a food source for birds, but the berries of the species it displaces are preferred. The canes are poor sources for wood, fodder, etc. Thus, the quality of the ecosystem is harmed. (U.S. Forest Service, 2013)

On the other hand, one could almost say that all plants were new at some point in prehistory, and that they were non-native when they first appeared. Many bring benefits, and indeed, many NNIPs were deliberately introduced by private or public efforts to reap those benefits (multiflora rose, for instance). However, at least one source concludes that the bias toward landscaping with introduced ornamentals has been so complete that in urban and suburban areas throughout the United States, the ecosystem is dominated by plant species that evolved in Asia, Europe, and South America. (Tallamy and Shropshire, 2008) It is just as if our native species had been replaced with invasive species from abroad.

NNIPs become monsters when they so dominate an ecosystem that they destroy it. In the United States they are estimated to cover an area “larger than the entire Northeast, from Pennsylvania to Maine.” They cost Americans about $138 billion per year in economic damages and control costs. (Dale Bosworth, U.S. Forest Service Chief, quoted in Kaufman & Kaufman, 2012, p.2) They are spreading at a rate somewhere between 1.3-25% annually.

I was writing tongue–in-cheek when I called NNIPs monsters that are overrunning America, but they are a serious problem. In my next post, I will report on an assessment of NNIPs in Missouri’s forests.

Sources:

Kaufman, Sylvan R., and Kaufman, Wallace. (2012). Invasive Plants: A Guide to Identification, Impacts, and Control of Common North American Species. Mechanicsberg, PA: Stockpole Books.

Tallamy, D.W. and Shropshire, K.J. 2008. Ranking Lepidopteran Use of Native Versus Introduced Plants. Conservation Biology. 23(4):941–947.

U.S. Forest Service. (2013) An Assessment of Invasive Plant Species Monitored by the Northern Research Station Forest Inventory and Analysis Program, 2005-2010. General Technical Report NRS-109. Available online at: http://www.nrs.fs.fed.us/pubs/43136.

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