In the understories of deciduous woodlands of the eastern United States it forms dense thickets, the shade of whose canopies prevent the growth of native shrubs, juvenile trees, and wild flowers. Uncontrolled, these growths result in almost monocultural thickets of Amur honeysuckle. The species gravely jeopardizes not only the diversity of the invaded ecosystems but even the regeneration of woodlands, because it reduces the growth and diversity of native seedlings. Additional studies indicate that it negatively affects birds and tadpoles.

The hard, woody vines twine tightly around host tree trunks and branches and cut through bark, causing death by girdling. On the ground, new vines germinating from seed or sprouting from rootstocks form dense thickets that smother and shade out native vegetation and impede natural plant community development. As girdled trees die, canopy gaps are created which increase the amount of sunlight reaching the forest floor. While this may temporarily favor some native species, it also stimulates vigorous growth and spread of wisteria.

Beefsteak plant grows along roadsides, ditches, forest margins, and on hillsides. It spreads to natural areas, especially disturbed areas. It can disrupt native ecosystems by outcompeting native plants. It is ordinarily avoided by cattle and has been implicated in cattle poisoning. Beefsteak plants are most toxic if cut and dried for hay late in the summer, during seed production.

Burning bush, also known as Winged spindle or Winged euonymus, can invade not only a variety of disturbed habitats including forest edges, old fields, and roadsides but also in undisturbed forests. Birds and other wildlife eat and disperse the fruit. Once established, it can form dense thickets, displacing native vegetation. It is native to northeastern Asia and was first introduced into North America in the 1860s for ornamental purposes. This plant is still sold and planted as an ornamental.

Invasive pears gain a foothold in agricultural or natural areas. Because they flower and set seed as young as three to five years old, they quickly spread and replace desirable plants in invaded areas. Once established in a fallow field or vacant lot, they bloom, fruit and sprout rapidly into thorny thickets and spread rapidly to assault new land. As with other woody invaders, pears threaten pastures and fields because grazing livestock do not eat them. If a farmer attempts to mow or bush-hog these pernicious pears, the stout thorns can puncture the tractor’s tires. If cut down and not treated with herbicide, new trees grow from the roots.

Plants form dense thickets; invading fields, fencerows, roadsides, forest understories, and riparian sites. They can shade out and exclude native understory species, perhaps even reducing tree recruitment. Native to Europe and Asia, Chinese privet was introduced in the United States in 1852 as an ornamental plant. It is commonly used as an ornamental shrub and for hedgerows.

Chinese silvergrass escapes from ornamental plantings and can form large clumps along disturbed areas, displacing native vegetation. The grass is also extremely flammable and increases fire risks of invaded areas. It is native to Asia and was introduced into the United States for ornamental purposes during the late 1800s.

English ivy is an aggressive invader threatening all levels of forested and open areas, growing along the ground as well as into the forest canopy. Vines climb up tree trunks and envelop branches and twigs, blocking sunlight from the host tree’s foliage, impeding photosynthesis. An infested tree will exhibit decline for years before it dies. The weight of vines also makes trees susceptible to blowing over in storms. This plant has been confirmed as a reservoir for bacterial leaf scorch (Xylella fastidiosa), which affects a wide variety of trees.

Japanese barberry invades a variety of habitats from shaded woodlands to open fields and wetlands. It is rapidly spread by birds that eat the berries thus dispersing the seeds. Since barberry is a low, dense shrub, it creates a microclimate habitat favored by ticks, buffering extreme temperature and humidity fluctuations in comparison to relatively taller and less dense native vegetation. Animals, including the primary reservoir of Lyme, the white-footed mouse, also find refuge under or around barberry, creating a higher density of Lyme-infected ticks. It is native to Asia and was first introduced into The United States in 1864 as an ornamental. It is still widely planted for landscaping and hedges.

Japanese spirea invades a variety of habitats including fields, forests, stream banks and many disturbed areas. Once established, it can form dense stands which displace native vegetation and close open areas. It is native to eastern Asia and was first introduced into the United States around 1879 as an ornamental.

Leatherleaf mahonia has large, sharp, holly-like leaves and produces yellow flower clusters in February, followed by purple berries. Birds eat the berries and disperse the seeds. It is native to China and has been planted as a showy ornamental in the USA. Leatherleaf mahonia is now invading woodlands in the southern United States. Volunteer plants are showing up in ditches and alongside the streets in Franklin Park.

Shrubs can grow over 15 ft. high in thickets that cast dense shade, suppressing native shrubs, small trees and herbaceous vegetation. A dense cover of young plants produced from seed and vegetative re-growth often blankets the ground in infested areas. Linden viburnum leafs out earlier in the spring and keeps its leaves later into the fall than most native vegetation, giving it a competitive advantage.

Mimosa invades any type of disturbed habitat. It is commonly found in old fields, stream banks, and roadsides. Once established, mimosa is difficult to remove due to the long lived seeds and its ability to re-sprout vigorously. Albizia julibrissin is native to Asia and was first introduced into the U.S. in 1745. It has been widely used as an ornamental.

Creeping Jenny can be found in a variety of different habitat types; however, it grows most vigorously and poses the biggest threat in moist areas such as wet meadows, swamps, floodplain forests, stream banks, bottoms, ditches, roadsides and along the banks of small water bodies. It can form a mat-like growth capable of excluding more desirable native plant species. It is now found across the United States and Canada.

Nandina, or Heavenly bamboo, is shade tolerant, which allows it to invade forest edges and interiors. Birds eat the berries and disperse the seeds. The berries are toxic to Cedar waxwings, one of our beautiful songbirds. Nandina is native to eastern Asia and India and was first introduced to North America in the early 1800s. It has been planted widely as an ornamental and often escapes from old plantings.

Norway maple is able to shade out native understory vegetation such as spring ephemerals, and eventually out-competes native tree species in the forest canopy. It is a prolific seed producer, and the wind disperse the seeds far and wide. Thus, it can reduce native species diversity and change the structure of forest habitats.

Royal paulownia is an aggressive tree that invades disturbed natural areas including forests, roadsides, and stream banks. It is native to China and was first introduced into the United States as an ornamental in 1840.

Running bamboo infestations are commonly found around old homesites and can rapidly expand in size. Bamboo can form dense, monocultural thickets that displace native species, prevent sunlight from reaching the forest floor, and prohibit native trees from regenerating the forest. Once this plant is established, it is difficult to remove. It is native to China and was first introduced into the United States in 1882 for ornamental purposes.

Vinca, also called periwinkle, has few pests or diseases outside its native range and is classified as an invasive species in many parts of North America. It forms dense mats that smother other plants and prevent native seeds from reaching the soil and germinating. Once established, it is difficult to eradicate, as its waxy leaves shed most water-based herbicide sprays.

White mulberrry is found throughout the United States, where it invades old fields, urban lots, roadsides, forest edges, and other disturbed areas. It poses an ecological threat by displacing native species, possibly hybridizing with and transmitting a root disease to the native Red mulberry. White mulberry is native to Asia and was introduced in colonial times as a food source for silkworms.

Wintercreeper is a vigorous vine that invades forest openings and margins. It grows across the ground, displacing herbaceous plants and seedlings, and climbs trees high into the tree canopy by clinging to the bark. Wintercreeper can overtake the underlying tree and the sheer weight of the vines renders the tree vulnerable to breakage during storms. Forest openings; caused by wind, insects, or fire; are especially vulnerable to invasion. Wintercreeper has been reported to be invasive in natural areas in most of the states in the eastern half of the U.S. It can tolerate a broad range of environmental conditions ranging from full sun to deep shade.