Research Projects:
INVASIVE EXOTIC PLANTS OF THE SOUTHEAST
Heather Alley, James M. Affolter and Jennifer Ceska
Heather Alley, James M. Affolter and Jennifer Ceska, "Invasive Exotic Plants of the Southeast," Public Garden, November 2002.
They receive less attention than the more familiar agricultural and rangeland weeds, but invasive plant species are severely disrupting southern forests and other native plant communities. They displace native species, destroy habitat and food for wildlife, alter hydrology and nutrient flow, and compete for pollinators and seed dispersers that native plants depend on. The financial cost is huge. The cost to our natural heritage is immeasurable.
Because the climate of the southeastern United States is similar to that of China and Japan, we are particularly vulnerable to destructive invasive exotics from those regions. The floristic similarity between East Asia and the southeastern United States is well known, with many shared genera and plant families. Unfortunately, many invasive Asian species also feel at home, but without natural pests, herbivores, and competition, they spread at alarming rates, disrupting the native plant communities. The ten plants that follow are among the most destructive invasive exotic species in the Southeast. They provide examples of the many ways invasive species wreak havoc on the lands they invade.
Elaeagnus umbellata
The autumn olive originates from China, Korea and Japan and was introduced to the United States in 1830. It has been used extensively for roadside plantings, wildlife habitat, strip mine revegetation, shelter belts, and as an ornamental. It is still commonly used in landscaping. It grows up to 20 feet, with a bushy, spreading habit. Spines on the twigs allow it to climb and overtop adjacent vegetation. Autumn olive is a vigorous species that can adapt to many environmental conditions. It spreads rampantly via seed, and has escaped throughout the South, invading disturbed areas and open natural lands.
Ligustrum sinense
Originally from China, Chinese privet has become one of the most ubiquitous and noxious weeds in the Southeast. It was introduced in 1852 as an ornamental hedge. When left unpruned, privet can reach 16 feet in height. Its small, black, berry-like fruits are eaten by wildlife, especially birds, which spread privet seed far and wide. It grows in disturbed areas such as roadsides and old fields, and spreads into forests. It is particularly prolific along rivers and has greatly altered riparian ecosystems in the Southeast, covering vast areas and crowding out virtually all native plant species.
Pueraria montana
Commonly referred to as "the plant that ate the South," the kudzu vine was introduced to the United States in 1876 as livestock fodder. It was widely distributed in the 1930s by the Soil Erosion Service (now the Soil Conservation Service) as a solution to agricultural runoff. Its rampant growth (up to one foot per day!) led the USDA to stop recommending it as a cover plant in 1953 and it has been listed as a southern weed since 1970. Covering an estimated seven million acres, kudzu is the poster child for invasive plants in the American South. It thrives under a wide range of conditions, especially mild winters and hot summers, and in almost any soil type. It is most commonly found along roadsides, abandoned areas, and at forest edges where it blankets enormous expanses of land. It also penetrates forests and smothers trees.
Microstegium vimineum
Once widely used as packing material for Chinese porcelain, the Asian grass microstegium, Japanese grass, or Nepal grass was first recorded growing in the United States in Tennessee in 1919. Probably mixed in hay and soil, it has spread to all states east of the Mississippi river, and Connecticut southward. Microstegium is an annual grass that forms large colonies, displacing native species of the forest understory. It is shade tolerant and does not persist in full sun. It reproduces prolifically from seeds that can survive in the soil for at least five years. It is dispersed by animals, floods, and human activity. Habitats most affected by microstegium include flood plains, and the banks of streams and rivers. It is also frequently abundant in damp fields, lawns, woodland edges, roadsides, and ditches. Unfortunately, deer do not eat microstegium, giving it an additional competitive advantage over many native species.
Wisteria sinensis and Wisteria floribunda
Chinese wisteria and Japanese wisteria were introduced in the early 1800s as showy, ornamental vines. Members of the bean family, wisterias bear abundant, pendulous clusters of fragrant lavender flowers in the spring. The woody, twining habit that makes them so popular for porches, gazebos, walls, and gardens, can be deadly to surrounding vegetation that they strangle or cover. Wisteria can smother and kill large trees, its height only limited by the structure that supports it. In forest edges, wisteria allows more light to penetrate as it chokes out shrubs and trees, which in turn allows the weed to further spread, forming dense, impenetrable thickets via vegetative and sexual reproduction. Areas commonly assaulted by its voracity include roadsides, ditches, and rights-of-way, all of which meet its full sun preference.
Albizia julibrissin
A member of the bean family, Mimosa, acacia, or silk tree is native to Asia, from Iran to China. In 1745, it was introduced to the United States as an ornamental tree noted for its brilliant display of fragrant, white to pink, puffball flowers and feathery leaves. Mimosa has spread rampantly via seed into disturbed areas from Virginia to Louisiana, and in California. It thrives best in full sun or partial shade, which restricts its spread into mature forests. However, it can take hold in riparian areas where it spreads rapidly, and is dispersed by water. It is most commonly found in disturbed areas such as fields, roadsides, and vacant lots.
Lonicera japonica
Japanese honeysuckle, native to China, Japan, and Korea, was introduced to the United States in 1806. This rapidly growing, evergreen, twining, vine, often utilized as a ground cover and stabilizer, has escaped cultivation and become widespread throughout native woodlands. It spreads rapidly from seed and vegetatively via runners forming dense, impenetrable mats. It has altered forest ecosystems in its path by crowding out native plants, including small trees, and providing openings for other invasive species.
Hedra helix
A well known, evergreen, clinging vine, English ivy has been cultivated since ancient times and was probably introduced to the United States by early European immigrants. English ivy is recommended by professionals as a groundcover and alternative to lawns. It is long-lived, vigorous and fast growing. These qualities allow it to invade natural areas. It spreads vegetatively and by seed into woods, hedgerows, fields, and marsh edges, particularly in disturbed areas. English ivy is destructive to natural areas at every level, forming dense mats on the ground, and gradually overtopping and collapsing large trees. Its range includes most of the eastern United States and all west coast states.
Hydrilla verticillata
Introduced just over 40 years ago in 1960 through the aquarium trade, hydrilla has become one of the most destructive aquatic weeds. Native to Australia, parts of Asia and Japan, hydrilla is well established in southeastern wetlands. Hydrilla spreads via seed and vegetatively and among water systems via water fowl and boats. It reproduces rapidly, clogging waterways, preventing recreational activities and destroying fish habitat. Millions of dollars are spent annually in attempts to control it.
Rosa multiflora
The multiflora rose, named for its prolific showy white blossoms that cover the shrub in mid-summer, was introduced in 1866 from Japan as a rootstock for ornamental roses. In the 1930s it began to be used for erosion control, wildlife cover, and along highways. The multiflora rose is a large shrub with arching branches and numerous thorns. It spreads rampantly via bird-dispersed seeds, and vegetatively, rooting where arching branches touch ground. Multiflora rose invades roadsides, water edges, and penetrates into deep woods, excluding other vegetation. It is a major problem in disturbed areas such as meadows and pastures, where it forms dense colonies that disrupt cattle grazing.
Resources
There are numerous sources of online information regarding invasive plant species. We found the following to be particularly helpful: