Garlic mustard is an extremely invasive non-native plant that can reseed prolifically and displace large areas of low-growing native plants.
A primary goal of the National Park Service is to preserve native plants and animals in the Great Smoky Mountains. Unfortunately, hundreds of non-native or “exotic” plants have been introduced by human activities. Exotics often out-compete natives and can displace them from the park. Exotic plants are species that have been introduced to an ecosystem by human activities. Usually exotics come from other countries or continents, but they may also come from other regions of the United States.
Because exotics grow in new environments that may lack natural controls (diseases, predators, parasites, climate, etc.) they often have an advantage over native species and can easily out-compete them for habitat. This threatens the survival of native plants and animals and may cause irrevocable changes to an ecosystem. Exotic plants also take an economic toll. Nationwide, it is estimated that exotics cost the United States over $50 billion per year in reduced crop yields, livestock range loss, and lawn, garden, and golf course maintenance expenses.
Exotic Plants in the National Park
Several factors make Great Smoky Mountains National Park especially vulnerable to invasions by exotic species. The park’s climate is relatively mild with abundant rainfall. Mountains, with their varying elevations and aspects, offer diverse habitats suitable for a wide variety of plants, both native and exotic. Climate and habitats in the Smokies also closely resemble those in parts of eastern Europe and central Asia. Consequently, plants introduced from these areas usually thrive in the Great Smoky Mountains.
In fact, botanists have identified over 380 species of exotic plants in the park. Some were brought in by early settlers; others were transported by wind, water, or animals from infested areas. Still others came in on fill dirt used in construction projects or were accidentally transported in by park visitors.
While the majority of the park’s exotic plants do not significantly alter the landscape or spread rapidly, 35 species are aggressive and do pose serious threats to the park’s natural ecosystems. These aggressive exotics include kudzu, mimosa, multiflora rose, bush honeysuckle, Japanese grass, Japanese spirea, and garlic mustard. Some are capable of growing and spreading rapidly and can completely dominate natural landscapes. Certain exotics also have the potential to cross-pollinate with similar native plants, thereby threatening the genetic integrity of the natives.
Controlling Aggressive Exotics
The park’s exotic plant control crew works to contain 60 species of invasive exotics at over 600 sites in the Smokies. The following section describes those species of greatest concern to Park Service exotic plant management staff.
Kudzu is a fast-growing Asian vine that covers some seven million acres of land (an area larger than Vermont) in the southeastern United States. Prior to 1953 the plant was widely grown as livestock forage and as a means of controlling erosion. Park crews have largely contained the spread of kudzu in the Smokies, though they continue to monitor 116 sites and treat them as needed.
Japanese Grass is pervasive in disturbed lowlands. It can rapidly replace native ground cover in moist, fertile areas such as Cades Cove and Sugarlands. Presently there is no efficient means of controlling Japanese grass over a large area and the plant will continue to gain ground until new treatments are developed.
Privet is native to Europe, Asia, and North Africa, but has been planted widely in this region as a hedge. Birds and other wildlife spread the seeds far and wide. Once sprouted, privet can form dense thickets which displace native plants. Park crews spend up to 550 work hours each year removing privet thickets.
Multiflora Rose was introduced over 40 years ago for wildlife cover, living farm fences, windbreaks, and roadside crash fences. It spreads rapidly and can form thickets which displace native species. Birds and other wildlife spread its prolific seeds (up to 1 million per plant). Multiflora rose is native to China and Japan.
Japanese Honeysuckle is a woody vine introduced for erosion control, wildlife cover, and as an ornamental. In the Smokies it is capable of out-competing native ground cover and overtopping shrubs and small trees. Its persistent green leaves photosynthesize in winter, increasing its ability to dominate native plants.
Mimosa is a medium-sized tree that is a continual problem along some roadsides and streams in the Smokies. It seeds prolifically and resprouts quickly when cut. Mimosa seeds may remain viable for 50 years or more. The tree is native to Asia and was introduced to this country in 1745. Park crews have spent up to 600 work hours per year controlling mimosa.
Garlic Mustard is a ground layer plant that can tolerate shade, making it especially threatening to the park’s densely forested environment. When introduced to disturbed areas or streamsides it can completely dominate the ground layer within ten years. It can also move from disturbed roadsides or trailsides to undisturbed forest. Garlic mustard is native to Europe. It can be controlled with prescribed fire as well as herbicides, cutting, and hand pulling.
Oriental Bittersweet is a serious threat to native plant communities due to its high reproductive rate and rapid growth. As a climbing vine it damages or kills native plants by girdling and shading. It can also hybridize with American bittersweet, leading to the native’s loss of genetic integrity. Oriental bittersweet is native to Japan, Korea, and China.
Musk Thistle is an herbaceous plant that can quickly invade disturbed areas such as roadsides, landscape scars, and flood plains. One plant can produce over 100,000 seeds. This native of Europe poses a threat to the park’s grassy balds and is a common contaminant in fill dirt.
Landscaping With Native Plants
Using native plants in gardens and landscaped areas preserves biological diversity and promotes our natural heritage. Natives are also better adapted to regional conditions and may require less watering, pesticides, fertilizer, and other maintenance. In addition, native plants provide food and shelter for a wide array of wildlife, including butterflies and migrating song birds. The following list includes a variety of attractive plants suitable for landscaping which are native to the area surrounding Great Smoky Mountains National Park. Most are readily available from native plant nurseries in Tennessee and North Carolina. Do not dig plants from the wild.
Red maple Acer rubrum
Sugar maple Acer saccharum
Yellow buckeye Aesculus flava
Pignut hickory Carya glabra
White ash Fraxinus americana
Black walnut Juglans nigra
Red cedar Juniperus virginiana
Sweetgum Liquidambar styraciflua
Tuliptree Liriodendron tulipfera
White pine Pinus stroba
Sycamore Platanus occidentalis
Chestnut oak Quercus prinus
Northern red oak Quercus rubra
Sassafras Sassafras albidum
Serviceberry Amelanchier arborea
Redbud Cercis canadensis
Flowering dogwood Cornus florida
Silverbell Halesia carolina
Witch-hazel Hamamelis virginiana
American holly Ilex opaca
Sourwood Oxydendrum arboreum
Staghorn sumac Rhus typhina
American mountain ash Sorbus americana
Sweetshrub Calycanthus floridus
Hearts-a-bustin Euonymus americanus
Wild hydrangea Hydrangea arborescens
Mountain laurel Kalmia latifolia
Spicebush Lindera benzoin
Flame azalea Rhododendron calendulaceum
Rosebay Rhododendron Rhododendron maximum
Mapleleaf viburnum Vibernum acerifolim
Columbine Aquilega canadensis
Jack-in-the-pulpit Arisaema triphyllum
Butterfly weed Asclepias tuberosa
White wood aster Aster divaricatus
Later purple aster Aster patens
Blue cohosh Caulopyllum thalictroides
Pink turtlehead Chelone lyonii
Bleeding heart Dicentra eximia
Joe-Pye weed Eupatorium fistulosum
Wild geranium Geranium maculatum
Sharp-lobed hepatica Hepatica acutiloba
Cardinal flower Lobelia cardinalis
Alumroot Heuchera americana
Turks-cap lily Lilium superbum
Cardinal flower Lobelia cardinalis
Bishop’s cap Mitella diphylla
Solomon’s seal Polygonatum biflorum
Fire pink Silene virginica
Bird-foot violet Viola pedata
Long-spurred violet Viola rostrata