Although some non-native plant species display colorful flowers and are popular as garden ornamentals, they can be highly invasive and destructive to a natural environment. Many introduced, or "exotic" plants were planted to decorate homes and gardens. Over the years, they have escaped cultivation and have infested natural areas. Because they are growing in an environment that lacks natural controls (diseases, predation), they have an advantage over native species and can easily out compete them for habitat. This causes an imbalance in the ecosystem and threatens the biodiversity of the area.
The Kentucky Exotic Pest Plant Council, Kentucky affiliate of the Southeast Exotic Pest Plant Council, has the responsibility of keeping a list of the most severely invasive plant threats to Kentucky. Their current list can be seen at http://www.se-eppc.org/ky/list.htm.
Kentucky's top 10 worst plant threats include:
Bush Honeysuckle - Exotic bush honeysuckles can rapidly invade and overtake a site, forming a dense shrub layer that crowds and shades out native plant species. They alter habitats by decreasing light availability, by depleting soil moisture and nutrients, and possibly by releasing toxic chemicals that prevent other plant species from growing in the vicinity. Exotic bush honeysuckles may compete with native bush honeysuckles for pollinators, resulting in reduced seed set for native species. In addition, the fruits of exotic bush honeysuckles, while abundant and rich in carbohydrates, do not offer migrating birds the high-fat, nutrient-rich food sources needed for long flights, which are supplied by native plant species. For more detailed information on bush honeysuckle and treatment methods, please visit http://www.nps.gov/plants/alien/fact/loni1.htm.
Bush Honeysuckle |
Kudzu |
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Kudzu - Few plants can survive once smothered by kudzu. It does not strangle competition, but simply blankets trees with a dense canopy, through which little light can penetrate. There is little spread by seed, so expansion of kudzu patches occurs mainly by rooting of runners at nodes. Adventitious rooting gives rise to large storage tubers that can survive repeated herbicide treatments over many years. For more detailed information on kudzu and treatment methods, please visit http://www.invasive.org/eastern/biocontrol/25Kudzu.html.
Winged Burningbush - This shrub has been widely planted in the eastern United States for its fiery-red autumn foliage, in private gardens as well as roadsides and other public lands. Its seeds are eaten and dispersed by birds and other animals, and this has contributed to its spread. Now widely naturalized and invading natural habitats, Winged Burningbush is considered a noxious weed. Although it continues to be promoted by the nursery trade, its potential for destroying native habitats makes it a poor choice for the garden. For more detailed information on winged burningbush and treatment methods, please visit http://www.nps.gov/plants/alien/pubs/midatlantic/eual.htm.
Winged Burningbush |
Garlic Mustard |
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Garlic Mustard - This shrub can invade a forest through a disturbance such as tree fall or trail construction. Along stream banks, the plant does exceptionally well because of the disturbance created by periodic flooding. Prolific seed production and lack of natural predators which might feed on garlic mustard allow it to quickly dominate the ground cover. Native herbs in competition with garlic mustard may suffer population declines. For more detailed information on garlic mustard and treatment methods, please visit http://www.invasivespeciesinfo.gov/plants/garlicmustard.shtml.
Multi-Flora Rose - This shrub has invaded a large number of habitats, from hillside pastures, fence rows, rights of way, and roadsides to forest edges and the margins of swamps and marshes. A single, vigorous, mature plant can produce up to half a million seeds annually. Where plants have become well established, a huge seed bank develops that can continue to produce seedlings for at least 20 years after removal of mature plants. Since the 1960s, multi-flora rose has become one of the most noxious weeds in the eastern United States. It is especially troublesome in regions with steep slopes, which prevent access by tractors or mowers for cutting this weed. Multi-flora rose forms dense, impenetrable thickets in many regions of the eastern United States. At least 10 states have passed noxious weed laws against it, and it is illegal to plant it in many areas, including Kentucky. For more detailed information on multi-flora rose and treatment methods, please visit http://www.invasivespeciesinfo.gov/plants/multiflorarose.shtml.
Multi-Flora Rose |
Oriental Bittersweet |
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Oriental Bittersweet - This shrub is a serious threat to plant communities due to its high reproductive rate, long range dispersal, ability to root sucker, and rapid growth rate. Climbing oriental bittersweet vines severely damage native vegetation by constricting and girdling stems. Vines can shade, suppress, and ultimately kill native vegetation. Oriental bittersweet has been shown to hybridize with the relatively rare American bittersweet. For more detailed information on oriental bittersweet and treatment methods, please visit http://www.invasive.org/eastern/eppc/bittersweet.html.
Japanese Knotweed - This shrub spreads quickly to form dense thickets that exclude native species and are of little value to wildlife, leading to it being described as an environmental weed. The extensive rhizome system of this weed can reach 15 to 20 meters in length, and enables the plant to achieve early emergence and great height, which combine to shade out other vegetation, and reduce native species diversity. At the end of the growing season, a mass of dead stems remains that further inhibits native plant regeneration and leaves river banks vulnerable to erosion as well as to flooding. For more detailed information on Japanese knotweed and treatment methods, please visit http://www.invasive.org/eastern/biocontrol/12Knotweed.html.
Japanese Knotweed |
Purple Loosestrife |
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Purple Loosestrife - The invasion of this plant alters the biogeochemical and hydrological processes in wetlands. The leaves of the purple loosestrife decompose quickly in the fall resulting in a nutrient flush, whereas leaves of native species decompose in the spring. This change in timing of nutrient release at a time of little primary production results in significant alterations of wetland function and could jeopardize detritivore consumer communities adapted to decomposition of plant tissues in spring. For more detailed information on purple loosestrife and treatment methods, please visit http://www.invasive.org/eastern/biocontrol/11PurpleLoosestrife.html.
Chinese Silvergrass - This plant forms extensive infestations by escaping from older ornamental plantings to roadsides, forest margins, and adjacent disturbed sites, especially after burning. Chinese silvergrass is highly flammable and a fire hazard. For more detailed information on Chinese silvergrass and treatment methods, please visit http://www.invasive.org/eastern/srs/CS.html.
Chinese Silvergrass |
Japanese Stilt Grass |
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Japanese Stilt Grass - Japanese stilt grass, also known as Nepalese browntop is especially well adapted to low light conditions. It threatens native plants and natural habitats in open to shady, and moist to dry locations. Stilt grass spreads to form extensive patches displacing native species that are not able to compete with it. The grass will readily invade areas subject to regular mowing, tilling, foot traffic, and other solid disturbing activities. For more detailed information about Japanese stilt grass and treatment methods, please visit http://www.nps.gov/plants/alien/fact/mivi1.htm.
What Can You Do To Help?
Each year, Bernheim Arboretum and Research Forest, the Southeast Exotic Pest Plant Council and the Environmental Resource Management Center at Northern Kentucky University publishes a poster of those plants that have proven to be invasive of our native habitats. These introduced plants are out-competing native species resulting in a reduction of plant diversity. We urge everyone to be on the lookout for these plants and avoid planting them in your yard. Instead, there are several similar plants that can provide similar enhancement to your environment. Please view the current and past year's "Kentucky's Least Wanted Plant" posters at http://www.se-eppc.org/ky/leastwant.htm.
Photo credits - these photos were obtained from several U.S. Forest Service Web sites and other state agency Web sites with permission.
