The Onslaught of Invasive Species
In the last one hundred or so years a new enemy of native biodiversity has become obvious, exotic invasive species. Today many believe them to be second only to loss of habitat as a threat in the Bluegrass as in the nation.
Invasive exotic species, like the zebra mussel, are species brought into North America from another country (i.e.“exotic”) that have no natural enemies here and that thus spread aggressively, crowding out or directly killing native species. (Not all exotic species are invasive, but, because so many are, people sometimes use the word “exotic” as though it means the same thing as “invasive.”) Many invasive exotic species were brought into this country on purpose, usually as ornamental plants, and only later were found to pose a threat; other invasive species have come in accidentally, often as part of commercial shipments of agricultural materials.
Japanese Hops (Humulus japonicus), which was imported into North America from eastern Asia before 1900, has only recently been recognized as a problem in the Bluegrass. The plant is a bine, i.e. it climbs by means of bristles rather than tendrils as vines do. In 2007 a landowner north of Frankfort on the Kentucky River alerted the Kentucky State Nature Preserves Commission (KSNPC) to the aggressive character of this plant on his land. KSNP staff then found it on a nearby preserve; and, during a ten-mile boat trip on the river to look for other occurrences, identified eighty-three other populations. Japanese Hops is now known to be well established throughout the Kentucky River corridor, from which it is likely to spread to other watersheds. The species crowds out native species and, by doing so, accelerates erosion of the river banks, because it eliminates plants whose roots hold the soil in place and does little to retain soil itself (1).
Kudzu (Pueraria Montana var. lobata) is found most widely in the southeastern United States, but it has spread into Kentucky and has been identified in Fayette, Franklin, Garrard, and Madison Counties in the Bluegrass. A climbing, perennial vine in the pea family, it smothers trees and other vegetation by completely covering them. Able to grow sixty feet per season, a vine may be as much as one hundred feet in length and have a stem up to four inches in diameter. The fleshy tap roots, from which thirty or more vines can grow, may be seven inches or more in diameter, six feet in length, and weigh four hundred pounds. The plant was deliberately introduced into the United States in 1872 from Asia and was planted in the south for forage and as an ornamental crop.
Other invasive plants that constitute established or increasing problems in the Bluegrass region include Amur Honeysuckle (Lonicera maackii), a bush honeysuckle that forms a shade so dense that other plants cannot grow beneath it; Autumn Olive (Elaeagnus umbellata), a shrub with silvery-backed leaves and small red fruit which appeal to birds, who scatter the seed; Garlic Mustard (Alliaria officinalis), an edible white-flowered, biennial herbaceous plant, found in small to extensive colonies; Japanese Knotweed (Polygonum cuspidatum), a semi-woody perennial with virulent rhizomes that allow a plant to regenerate even after it has been almost completely pulled up; Multiflora Rose (Rosa multiflora), an import from Asia, now found in pastures, roadsides, floodplains, woodland edges, and sunny spots in the forest; Purple Loosestrife (Lythrum salicaria), a herbaceous species with tall, attractive spikes of purple flowers, which can produce as many as 2.5 million seeds per plant; Tree of Heaven (Ailanthus altissima), a tree from Asia, which can grow 2.5 feet per season and spreads by means of sprouts and highly viable seeds; and Winter Creeper/Climbing Euonymus (Euonymus fortunei), an evergreen perennial vine that covers the ground and grows up trees in wooded areas. Most unfortunately these and other invasive plants infest many of our parks and preserves.
The Early Detection and Distribution Mapping System of the Exotic Pest Plant Council maps the ranges of exotic plants in Kentucky. Not all the plants shown are highly invasive but the invasive species are included. The Kentucky maps can be accessed at http://www.se-eppc.org/eddMapS/kentucky.cfm .
Arguably the most destructive exotic in the history of the Bluegrass was not a plant, but a fungus from China or Japan that caused the Chestnut Blight, a disease that virtually eliminated the American Chestnut from forests in this region and throughout the east early in the twentieth century. The American Chestnut Foundation and other organizations are now working with some success to create and propagate blight-resistant chestnut trees.
Two major current threats are insects, the Emerald Ash Borer and the Hemlock Woolly Adelgid. The borer, an insect from Asia that, as its name suggests, kills ash trees, is moving towards Kentucky from the North and has been found in Cincinnati. Traps to catch and identify the insect should it enter Kentucky have been put in place in Boone, Kenton, and Campbell Counties. If the insect is found, a quarantine will be established. The Hemlock Woolly Adelgid, another insect from Asia, which attacks Eastern Hemlock and Carolina Hemlock, is active in the southeastern part of the state and has been found on urban trees in Oldham County. Researchers are treating the outbreaks as best they can. Hemlocks are a major element in the forests of eastern Kentucky, and are grown as ornamental trees in the Bluegrass.
Some troublesome species are native rather than exotic. Canada Geese have become pests in some areas of the Bluegrass where they congregate in large numbers and have taken to staying year round rather than migrating north to breed. Their droppings and their noise may disturb people living ponds and wetlands. Where ginseng is grown, wild turkeys (which have bred with domestic turkeys) cause a problem because they are voracious understory eaters and destroy the ginseng seeds that they ingest by breaking them in their craws. Deer have become a problem to gardeners in some locations, because of their numbers and their fondness for munching on fruits and vegetables.
Numerous organizations in Kentucky work on ridding specific areas of invasive species. Once an invasive plant has taken over an area, it is usually extremely difficult, if not impossible, to get rid of it, however. Many died-in-the-wool environmentalists find that they have to use herbicides if they hope to root out an infestation; and KSNPC in fact recommends this method for Japanese Hops. The best means of thwarting invasive species is prevention, not allowing an invasive plant or animal to enter an area in the first place.
With plants a simple step that can be taken is not to plant invasive species in a garden or on a farm from which they can spread. Another is to persuade stores to stop selling invasive species. In the last couple of months the author has seen stores in Lexington selling both Winged Burning Bush (sh (Euonymus alata) and Common Periwinkle (Vinca minor), which are invasive in Kentucky. Stores should be required to stop selling species of plants and animals that are invasive in the state.
--Mary Byrd Davis
1. Andrew Berry, “Japanese Hops Emerges as an Aggressive Invasive plant in Kentucky,” Naturally Kentucky, Spring 2008, no. 58, pp. 4-5.
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