aka: Exotic Plants
According to the U.S. Department of Agriculture (USDA) Forest Service, an invasive species is “a species that is non-native or alien to the ecosystem under consideration and whose introduction does or is likely to cause economic or environmental harm or harm to human health.” As such, there are a suite of negative effects from exotic plant species that include replacing rare and endangered species, hybridizing and competing with native species, killing trees and shrubs, altering hydrological patterns and stream function, preventing forest regeneration, possibly containing toxins that may be lethal to certain animals, changing fire patterns, and harboring pathogens. The cost to control invasive species and the damages they cause to property and natural resources in the United States is estimated at $137 billion annually.
In Arkansas, non-native plant species make up about twenty-three percent of the Arkansas flora. Three percent of Arkansas forestland is covered by invasive species such as the chinaberry tree, princess tree, Bradford pear, Chinese tallow tree, Negundo chaste tree, Chinese flame tree, tree of heaven, tungoil tree, golden-rain tree, and mimosa; invasive shrubs, including Chinese and European privets, glossy privet, silverberry, and bush honeysuckle; invasive vines such as winter creeper, kudzu, Japanese honeysuckle, Chinese wisteria, English ivy, and non-native vincas; invasive grasses and canes including running monkey grass, golden bamboo, bermudagrass, Johnson grass, and tall fescue; invasive ferns and forbs such as Japanese climbing fern and Chinese lespedeza; and the aquatic and noxious weeds hydrilla and giant salvinia.
Some Invasive Trees
Bradford or Callery pear trees (Pyrus calleryana) originated in China and Vietnam and were introduced into the United States in 1909 by the USDA as ornamental trees. This flowering tree was assumed to be sterile (but is not) and became known for its weak branch structure that cannot withstand ice storms. They have a lifespan of 20–25 years, and blooming trees are usually indicative of early spring in Arkansas. These trees are aggressive and can quickly crowd out native species.
The Chinese flame tree (Koelreuteria bipinnata) is a small to medium-sized tree that is native to southwestern China. It is occasionally cultivated in the southern United States for ornamental purposes because of its showy flowers and fruits and its tolerance of a wide range of soil types. Numerous K. bipinnata plants were discovered growing in two places on the Ouachita Baptist University campus in Arkadelphia (Clark County). Although it is too early to discern whether K. bipinnata will become invasive in the state, this tree has shown the ability to escape cultivation, reproduce successfully, and establish itself in Arkansas’s flora.
Koelreuteria bipinnata is not the only species of Koelreuteria to be documented in the Arkansas flora. Golden-rain tree (Koelreuteria paniculata) was discovered in 2006 on the Hendrix College campus in Conway (Faulkner County) and in Hot Springs (Garland County). This indicated that the non-native K. paniculata is spontaneous, does reproduce successfully, and could potentially establish in the state.
The Chinese tallow tree (Triadica sebifera) is a short-lived, fast-growing tree native to eastern Asia that has become naturalized throughout the southeastern United States from North Carolina to eastern Texas and westward to California. It was originally introduced into the United States by the work of French botanist François André Michaux (1770‒1855) during the late 1700s. Chinese tallow trees are used as an ornamental plant due to producing an attractive fall coloration; however, they are considered a weed. They tolerate a wide range of environmental conditions and occur in more than fifteen counties in Arkansas.
Mimosas or silktrees (Albizia julibrissin) are small, 20–40-foot-tall short-lived legume trees that reproduce by their abundant root sprouts and seeds. It was introduced from Asia (Iran to Japan) in 1745 as a traditional ornamental plant. Mimosas can grow in a variety of soils, produce large seed crops, and quickly re-sprout when cut or top-killed. It is also a strong competitor to native trees and shrubs in open areas or forest edges. Dense stands of mimosa severely reduce the sunlight and nutrients available for other plants. It occurs on dry-to-wet sites seldom above an altitude of 900 m (3,000 ft.) and is especially common along stream banks, preferring open conditions but also persisting in shade.
The chinaberry tree (Melia azedarach), an introduction from Asia in the mid-1800s, is a deciduous tree reaching up to 15 m (50 ft.) in height and 60 cm (2 ft.) in diameter. It has many branches with multiple boles (stems or trunks), lacy dark-green leaves with a musky odor, and clusters of lavender flowers in spring yielding tenacious, poisonous yellow berries. This tree out-competes native vegetation due to its high relative resistance to pathogens and insects. Its leaf litter raises soil pH, thus altering loam conditions for native plants and seed germination. It was widely planted as a traditional ornamental around home sites. It is commonly observed on roadsides and at forest margins but is rare at high elevations.
The tree of heaven (Ailanthus altissima) is also known as ailanthus, Chinese sumac, and stinking sumac. It is a rapidly growing, mostly deciduous tropical tree that can reach 24 m (80 ft.) or more in height. This tree was brought into North America from China by a gardener from Philadelphia, Pennsylvania, in 1784, and by 1840, it was commonly available from nurseries. Tree of heaven is widely distributed across the United States, occurring in at least forty-two states, from Maine to Florida and west to California. Interestingly, all parts of the tree, especially the flowers, have a strong, unpleasant odor. Once established, it can quickly take over a site and form a dense thicket. Ailanthus trees also produce toxins that prevent the establishment of other plant species. The root system is aggressive enough to cause damage to sewers and foundations. Ailanthus has also become an agronomic nuisance and may occur as seedlings that pop up by the hundreds in recently planted fields, or as persistent thickets in rocky, untillable areas.
The Negundo chaste tree (Vitex negundo) is a large deciduous shrub or small tree that grows to a height of 8 to 9 m (26.2 to 29.5 ft.). It is native to Europe, Asia, and possibly portions of North Africa. Vitex negundo has been documented in Florida, Louisiana, Maryland, Ohio, Oklahoma, Texas, and Arkansas (Baxter, Clark, Garland, Miller, Pulaski, and Yell counties).
The tungoil tree (Aleurites fordii) is a small to medium-sized tree that is native to China. It is occasionally planted or cultivated in the southern United States from eastern Texas to Florida. Several specimens were discovered on the campus of Henderson State University in Arkadelphia in 2007. Further research is needed to determine whether A. fordii will become invasive in Arkansas; however, it has shown the capacity to reproduce successfully, escape cultivation, and establish itself in the Arkansas flora.
Some Invasive Shrubs
The Chinese privet (Ligustrum sinense) was introduced from China into the United States in 1852. It is a semi-evergreen, shade-tolerant, tall shrub or small tree growing to about 9 m (30 ft.) tall with showy clusters of small white flowers. It is an aggressive and problematic invasive, often forming dense thickets, particularly in bottomland forests and along fencerows, thus gaining access to forests, fields, and rights-of-way. It spreads quickly and replaces native underbrush in Arkansas forests.
The glossy privet (Ligustrum lucidum), an introduction from China, Japan, and Korea, is a fast-growing evergreen tree approximately 8 to 14 m (25 to 40 ft.) in height. It has a dense canopy of bending branches composed of glossy green leaves that have narrow, translucent margins. Both leaves and fruit are toxic to humans. If not controlled, it has the potential to replace mid-canopy trees in forests and completely dominate an area of forest or forest fragments. It often grows along roadsides, in old fields, and in other disturbed habitats and in a variety of undisturbed natural areas.
Silverberry (Elaeagnus spp.) are native to temperate and subtropical regions of Asia. They are deciduous or evergreen shrubs or small trees. Many species of Elaeagnus harbor nitrogen-fixing organisms in their roots, so they are able to grow well in low-nitrogen soils. This adaptation results in multiple negative ecological consequences. They become invasive in many locations where they are established as exotic species, and in many world regions, two species, silverthorn (E. pungens) and autumn olive (E. umbellata), are currently rated as category II noxious invasive species.
Some Invasive Vines
Japanese honeysuckle (Lonicera japonica) is native to eastern Asia, including China, Japan, and Korea. It is a multi-stemmed and arching-branched twining vine able to climb up to 10 m (33 ft.) high or more in trees. It is used as an ornamental and is a significant food source for deer, rabbits, hummingbirds, and other wildlife. However, it destructively grows and chokes native shrubs and trees, and can also form mat-like monocultures that prevent the establishment of native species. The aggressive displacement of this vine poses a long-term threat to future generations of native forests. It is also very difficult to manage in semi-wild areas such as in large rural yards and is virtually impossible to control in edges of woodland zones due to its rapid spread via tiny fruit seeds.
English ivy (Hedera helix) was introduced from Europe in colonial times. It is an evergreen woody vine climbing to 28 m (90 ft.) by clinging aerial roots and trailing to form dense ground cover that controls all levels of disturbed and undisturbed forested areas. As the ivy climbs in search of increased light, it overwhelms and kills branches by blocking light from reaching the host tree’s leaves. The host tree eventually dies entirely from this stealthy and steady weakening. It matures at about ten years into erect plants or branches with unlobed leaves and terminal flower clusters that yield purplish berries. This vine thrives in moist open forests but is adaptable to a range of moisture and soil conditions, including rocky cliffs. English ivy spreads locally through vegetative growth, and new plants can grow from cut or broken pieces of stems that are able to root in the soil. This vine is toxic to humans if eaten and is capable of triggering dermatitis in hypersensitive or immunocompromised individuals.
Kudzu (Pueraria montana var. lobata) was introduced in 1876 at the Centennial Exposition in Philadelphia, Pennsylvania, where it was used in a Japanese government display garden. It was planted widely as an ornamental vine for its abundant vegetation and sweet-smelling flowers. In the 1920s, it was promoted as a forage plant, and by the next decade, the Soil Conservation Service encouraged landowners to plant it for erosion control. The Civilian Conservation Corps (CCC) planted it, and farmers were paid as much as $8.00 per acre to plant fields of the vine in the 1930s and 1940s. Not until the 1950s did the U.S. government stop suggesting planting of kudzu. In 1970, the USDA asserted that kudzu was a noxious weed, and, in 1997, kudzu was federally listed as a noxious weed.
Kudzu is a deciduous trailing, twining, mat-forming, ropelike woody leguminous vine, 10 to 30 m (35 to 100 ft.) long with three-leaflet leaves. Thick stands are exemplified by thousands of single-colored plants covering everything in their range. Kudzu kills or degrades other plants by smothering them under a solid blanket of leaves, by girdling woody stems and tree trunks, and by breaking branches or uprooting entire trees and shrubs through the force of its weight. Once established, kudzu can grow rapidly, extending as much as 30 m (100 ft.) per season at a rate of about 0.3 m (1 ft.) per day. Kudzu grows best in well-drained degraded or eroded land or in disturbed, sandy, deep-loam soils in full sun. It will, however, invade well-drained acid-soil forests. It does not grow well or at all in wet bottomlands or in thin hard-pan soils. Kudzu can persist on the floor of a closed canopy forest.
Invasive Grasses and Canes
Tall fescue (Lolium arundinaceum) was introduced from Europe in the early to mid-1800s. Recognized as a valuable forage grass in 1930s, it is now widely distributed over most of the globe. Tall fescue occurs throughout the continental United States and has been reported to be invasive in natural areas in numerous states, including Arkansas. In fact, it is among the most pervasive and detrimental of the state’s invasive species. This grass is drought resistant and able to grow in a variety of soils, spreads rapidly, and grows in dense, solid stands capable of outcompeting almost all types of native plants in Arkansas. It was originally established widely for turf, forage, soil stabilization, and wildlife food plots. Tall fescue is an erect, tufted cool-season perennial grass 60 to 120 cm (2 to 4 ft.) in height, and it invades native grasslands, savannas, woodlands, and other high-light natural habitats. This grass grows on wet to dry sites as tufted clumps or small to extensive colonies along forest margins and rights-of-way, and widely escaped to invade new forest plantations, roads, openings, and high-elevation mountain summits (balds). Based on misguided advice for conservation purposes, many thousands of acres of native prairie in the Midwest have been seeded with tall fescue. In the Ozarks, woodlands and barrens were converted to tall fescue pasture to augment grazing income. Plant communities dominated by L. arundinaceum are often not diverse in other plant species. In addition, alkaloids produced by endophyte-infected tall fescue may be toxic to small mammals and of low palatability to ungulates such as cattle, deer, and elk.
Johnson grass (Sorghum halepense) is a grass of the Mediterranean region; it was introduced purposely into South Carolina as a forage crop in the 1800s. It is now found in nearly every state, with the exception of some northern states, but especially in the southern half of the United States, including most of Arkansas, where it continues to spread by seed dispersal in agricultural machinery. Johnson grass grows best in fertile, well-drained soils in a variety of disturbed sites, including roadsides, ditchbanks, and fields. It can also be found in orchards, vineyards, and cotton fields. Considered one of the world’s top ten noxious weeds in sites where corn, soybeans, cotton, and sugarcane are grown, it hybridizes with sorghum. Johnson grass grows rapidly, is highly competitive with crops (reducing harvest yields), and can be very difficult to control. Healthy plants can provide good forage for livestock; however, foliage of S. halepense and other sorghums can produce toxic amounts of hydrocyanic acid when exposed to frost, stressed by drought, or damaged by trampling or herbicides and may be toxic to livestock when ingested.
Bermudagrass (Cynodon dactylon) was introduced from Africa and is a highly variable sod-forming perennial with extensive creeping rhizomes and stolons. Bermudagrass is commonly grown as durable turf or forage in tropical to warm temperate regions nearly worldwide. Numerous hybrids and strains have been developed, including some that tolerate cooler conditions. Because of its vigorous snaking habit, this grass is a noxious weed in many situations, especially in warm, moist climates. Human contact with plants can cause dermatitis in hypersensitive individuals, and its pollen is a common allergen. Mature C. dactylon pastures have occasionally been associated in livestock photosensitization or neurological syndromes, especially in late fall or early winter.
Golden bamboo (Phyllostachys aurea) is native to Asia (China and Japan) and was introduced in Alabama in 1882 as an ornamental and since has been widely planted for fishing poles. This bamboo is prominent in the southeastern United States as far north as Maryland and west to Arkansas and Texas and farther west and north to Oregon. It grows to 5 to 12 m (16 to 40 ft.) in height and consists of two parts: (1) the aboveground jointed stem called a culm, and (2) the underground jointed rhizome that possesses true roots. Infestations of bamboo displace native vegetation, alter habitat, and upset food chains. At streams, bamboo leaf litter alters aquatic food webs starting with litter-feeding stream invertebrates. It is often found as dense thickets along roadsides and residential rights-of-way but will also invade secondary forests, clearings, and forest edges.
In June 2021, a U.S. Department of Agriculture botanist spotted a patch of Cogongrass, native to Southeast Asia, in Helena-West Helena (Phillips County) alongside Highway 49. The grass is known to have a devastating effect upon plant species nearby.
Some Invasive Ferns and Forbs
Chinese lespedeza (Lespedeza cuneata) was introduced in Arlington, Virginia, via Japan in 1899, and soon thereafter in north-central Tennessee, where it escaped. It is a perennial ascending-to-upright leguminous forb, 1 to 2 m (3 to 6 ft.) in height. Government programs promoted plantings of L. cuneata for erosion control. It is still planted for quail (Coturnix coturnix) food plots and soil stabilization. However, L. cuneata is primarily a threat to open areas such as meadows, prairies, open woodlands, wetland borders, and fields. It forms dense stands by sprouting stems from rootcrowns that prevent forest regeneration and land access. Once it gains a grip, it can crowd out native plants and develop an extensive seed bank in the soil, guaranteeing its long residence at a site. Established dense stands of lespedeza suppress native flora, and its high tannin content makes it unpalatable to native wildlife as well as livestock.
Japanese climbing fern (Lygodium japonicum) is native to East Asia and tropical Australia and was introduced from Japan in 1930s. It was first discovered in Georgia and is an ornamental still being spread by naïve gardeners. This fern can be found in the southeastern United States, from the Carolinas south to Florida, and along the Gulf Coast to Texas and Arkansas. It is a perennial viny fern, up to 30 m (90 ft.) long, which climbs and twines, with lacy finely divided leaves along green to orange to black wiry vines, often forming mats of shrub- and tree-covering infestations. Once established, and if left uncontrolled, L. japonicum will shade out entire trees. It also produces a thick ground cover, preventing native seed germination. Japanese climbing fern is found along highway rights-of-way, especially under and around bridges, invading into open forests, forest road edges, and stream and swamp margins. Scattered in open timber stands and plantations, it can increase in cover to form mats, smothering shrubs and trees. This fern is also found in sunny or shady locations, usually in damp areas such as the edges of swamps, marshes, lakes, creeks, hammocks, and upland woodlands.
Some Invasive Aquatic Weeds
Hydrilla (Hydrilla verticillata) is thought to have originated on the Indian subcontinent and been introduced into North America in the mid-to-late 1950s by the aquarium trade. It has become common along the Atlantic Seaboard and southern states, including Arkansas, where it was found in Lake Ouachita and DeGray Lake in the late 1990s. Hydrilla is thought to have gotten its start there after being discarded from aquariums or by the nursery industry. It is actually an aggressive perennial herb (not a seaweed) with long stems that branch at the water’s surface, forming dense mats that can extend up to 10 m deep. Once established, it disrupts aquatic ecosystems in a number of ways, including: (1) blocking the sunlight from reaching native plants, (2) raising water pH and temperature, (3) affecting water flow, (4) lowering dissolved oxygen levels in aquatic environs, and (5) altering in other ways the chemicophysical characteristics of lakes. In addition, recreational activities like swimming and boating can be obstructed. Hydrilla potentially affects power generation by clogging dams, and it can promote mosquito habitat. Once introduced and established, hydrilla is easily spread through boating and fishing activities and by waterfowl.
Giant salvinia, or African Kariba weed or giant water spangles (Salvinia molesta), was recognized as an aggressive, sterile weedy clone and a distinct species in Africa, a pentaploid of hybrid origin, possibly from Brazil. It was first introduced into the United States as a water-garden plant in the 1980s and then spread across the southeastern United States. In Arkansas, biologists with the Arkansas Game and Fish Commission confirmed the presence of giant salvinia in a small portion of Lake Erling (Lafayette County). This represents the second occurrence of the invasive plant in Arkansas, with the first report being in 2017 from Smith Park Lake (Miller County). The most likely source of the infestation was from an angler or hunter transporting the plant to the lake accidentally after boating in an area where the plant had already become established. Giant salvinia is a free-floating (rootless) South American aquatic fern, similar in appearance to duckweed but much larger. It stays at the water’s surface and can rapidly cover a large area and choke out all life in the water beneath. Emergent groups of leaves (fronds), oblong and flat or semi-cupped, grow in chains and float on the water surface, forming dense mats. These mats shade out native aquatic species and reduce dissolved oxygen levels in the water. Agricultural water use is impacted, as salvinia obstructs intake pipes for irrigation. Recreational fishing and boating may be hindered by dense mats. Salvinia flourishes in slightly acidic, high-nutrient, warm, slow-moving freshwater environments. It is found in streams, lakes, ponds, ditches, and even rice fields. Salvinia is resistant to periods of low temperature, dewatering, and elevated pH levels but has a low tolerance to salinity. Giant salvinia is currently one of the newest, most dangerous invasive aquatic plants in Arkansas. It damages aquatic ecosystems by outgrowing and replacing native plants that provide food and habitat for native animals and waterfowl.
Some Arkansas cities have adopted plans to help slow the spread of invasive plants. In Fayetteville (Washington County), for example, the city council adopted an ordinance (No. 5820) on November 3, 2015, to establish a list of eighteen invasive plants to be restricted from being installed in new developments that require a landscape plan review by an urban forester. They also developed an educational packet that identified each of the eighteen invasive plants and recommended appropriate plant species for trees, shrubs, or ground cover. The purpose was to encourage all property owners to identify, remove, and replace invasive plants from the landscapes around their homes and businesses with alternative native species.
For additional information:
Arkansas Vascular Flora Committee. Checklist of the Vascular Plants of Arkansas. Arkansas Vascular Flora Committee. Fayetteville: University of Arkansas, 2006.
Burrows, G. E., and Ronald J. Tyrl. Toxic Plants of North America. Ames: University of Iowa Press, 2001.
Forno, I. W., and K. L. S. Harley. “The Occurrence of Salvinia molesta in Brazil.” Aquatic Botany 6 (1979): 185–187.
Griffiths, M. Index of Garden Plants. Portland, OR: Timber Press, 1994.
“Invasive Plants and Native Alternatives.” City of Fayetteville, Arkansas. https://www.fayetteville-ar.gov/3028/Invasive-Plants-and-Native-Alternatives (accessed April 13, 2021).
Langeland, K. A., and K. Craddock Burks. Identification and Biology of Non-Native Plants in Florida’s Natural Areas. IFAS Publication SP 257. Gainesville: University of Florida, 1998.
Peck, James A., and Brett E. Serviss. “New and Noteworthy Collections for Arkansas.” Sida 22 (2006): 817‒820.
Serviss, Brett, Nicole Freeman, Joslyn Hernandez, Allen Leible, and Chris Talley. “Tungoil Tree (Aleurites fordii Hemsl.) (Euphorbiaceae): New to the Arkansas Flora.” Journal of the Arkansas Academy of Science 61 (2007): 128‒130. Online at https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=1483&context=jaas (accessed April 13, 2021).
Serviss, Brett, Nicole Freeman, Joslyn Hernandez, Allen Leible, Chris Talley, and Brent Baker. “Negundo Chaste Tree (Vitex negundo L.) (Verbenaceae): New to the Arkansas Flora.” Journal of the Arkansas Academy of Science 61 (2007): 131‒133. Online at https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=1484&context=jaas (accessed April 13, 2021).
Serviss, Brett E., Nicole Freeman, and Sarah Melancen. “Chinese Flametree (Koeireuteria bipinnata Franch.) (Sapindaceae) New to the Arkansas Flora.” Journal of the Arkansas Academy of Science 60 (2007): 197‒199. Online at https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=1524&context=jaas (accessed April 13, 2021).
University of Arkansas Cooperative Extension Service. Arkansas Invasive Pests. Online at https://www.uaex.edu/environment-nature/ar-invasives/ (accessed April 13, 2021).
University of Arkansas Division of Agriculture and Arkansas State Plant Board. Top Ten Invasive Species of Concern in Arkansas. Online at https://www.uaex.edu/farm-ranch/pest-management/weed/Invasive%20weeds.pdf (accessed April 13, 2021).
Vines, R. A. Trees, Shrubs, and Woody Vines of the Southwest. Austin: University of Texas Press, 1960.
Walkingstick, Tamara. Arkansas Invaders: Invasive Species in Arkansas Forests. U of A Division of Agriculture Research and Extension.
Williamson, M. H. Biological Invasions. London: Chapman and Hall, 1996.
Chris T. McAllister
Eastern Oklahoma State College
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