Wildlife and the Outdoors


Exotic Invasive Plants in Alabama


Thagard R. Colvin, Wildlife Biologist


     People have been enamored with exotic plants and animals for centuries. It seems we are looking for something bigger, better and showy. Most imported exotic plants and animals are soon eliminated by forces in their new environment, but not all.

     A few exotic species of animals introduced to North America, such as the ring neck pheasant, honeybee and rainbow trout have proved valuable. The same might not be said for the English sparrow, European starling and red imported fire ant.

     Many introduced exotic plants such as cotton, peanuts and winter cereal grains have been an essential part of American society, but many other introduced plants have been labeled as invasive. Many of the invasive plants came from Asia and were introduced as ornamental plantings, for erosion control or as livestock food plants. A major problem with these plants is that they have no natural predators in America; therefore, they can out-compete and replace native plants.

     Chinese privet, a member of the ash family, was brought to the Southeast by the early 1900s as an ornamental plant and especially used for manicured hedge borders. This evergreen shrub grows into small trees and makes dense thickets. It is most invasive of creek and river bottoms. Privet stands become so dense that they can out-compete native trees and shrubs, making it difficult for man and wildlife to move through them.

     Chinese privet is spread by birds eating the small, black waxy seed and later depositing the seed miles from where it was eaten. This plant has very little wildlife value other than the fruit is eaten by some birds. Deer will browse very young sprouts of privet but not vigorously. Privet hedges routinely affect open wildlife habitat and far outweighs any positive values. Control of Chinese privet in large patches may eventually require treatment with herbicides, although mechanical preparation with heavy equipment may need to precede any herbicide.

     Three exotic invasive trees, chinaberry, tallow tree (popcorn tree), and silk tree (mimosa) were introduced into the United States in the early 1800s or 1900s as ornamentals. These trees are still rapidly spreading and are competing with and destroying our native flora.

     The tallow tree, which grows to a height of 50 feet, is especially invasive of wet areas including stream bottoms. Tallow trees make beautiful scarlet foliage in the fall and are still being sold in nurseries for landscaping because of this feature. The fruit is a waxy cluster that resembles a popped kernel of corn and is readily eaten by some birds. As with the Chinese privet, birds are a major factor in seed dispersal. Also, flood waters will move and spread seed in stream bottoms. Tallow trees are prolific seed producers and three-year-old seedlings will bear fruit. These trees can also withstand flooding and are resistant to fire. Herbicides will need to be used to control established stands of tallow trees.

     The silk tree, or mimosa, is a small tree of the legume family. It produces attractive pink flowers and will make a small shade tree of 10-50 feet in a few years. The mimosa produces abundant pods of hard, waxy seeds that float on water and remain viable for many years. It can also spread by root sprouts. Thick stands of mimosa will quickly invade old fields, fence rows and other idle land.

     Silk tree fruit and foliage are of no apparent value to wildlife, but this exotic tree out-competes native species that are. Small mimosa trees can be pulled up and individual trees removed, but large patches of silk tree will require herbicide treatments and possibly mechanical removal.

     Chinaberry was introduced as a quick growing shade tree and is often found around abandoned home sites. The seed, which is poisonous to livestock and other animals, is spread mechanically by forestry equipment. Chinaberry trees create dense stands and suppress native vegetation, creating masses so thick that access is severely limited. Control of this species will eventually need herbicide control since mechanical manipulation will only spread seed and root sprouts.

     Several other exotic invasive plants are ever increasing and causing problems to native flora. These include ailanthus, paulownia, and Russian olive trees, as well as shrubs like silverthorn, autumn olive, European privet, Japanese privet and several species of Asian bush honeysuckle. Invasive vines to be aware of include kudzu, Chinese wisteria, and climbing euonymus. Invasive grasses to watch out for are cogongrass, giant reed, Chinese silvergrass and Nepalese browntop.

     Before using a herbicide on any of the plants listed in this article, consult your local Extension office, registered consultant forester or a county forester. They can provide you with information on products, rate, method of application, time of application and necessary precautions to take. Treatments may take several years and should be monitored for at least 10 years after the last treatment.

     For more information, contact Thagard R. Colvin, Wildlife Biologist at 110 South 3-Notch street, Andalusia, AL 36420.