Q. I want to do some planting on my property for wildlife and to protect my stream banks from erosion. Should I use exotics or native species?

A. First, I think it is important to understand what one means by calling a plant, shrub or tree native or exotic. Native species are those that have not been introduced by human activity. Native species have evolved over centuries with the environmental, physical and biological factors of a specific area. The physical factors include soil types, temperature and weather, rainfall, and pH. Biological factors include a plant species’ relationship to other types of flora and fauna, which also inhabit the same area. Consequently, a native species is uniquely adapted to local conditions and the area’s wildlife species.

If the plant, shrub or tree species you are considering does not fit the qualifications outlined here, then it is probably an exotic. If you decide to plant exotics, and I hope you reconsider, keep in mind that exotics have been known to cause greater problems than benefits. Some exotics have become extremely invasive and destructive. One such species many people are familiar with is the kudzu, which has taken over vast areas throughout the south

Why, you might ask, have kudzu and other exotic plants become a problem? To answer this, you will have to refer back to the definition of a native species. As indicated, native species have developed over time a complex relationship with other species of flora and fauna occupying the same area. Two inhibiting factors that control the progression of native species are disease and insects. An exotic species brought into an area comes with no such controls. They may not be susceptible to disease and insects, which would normally hold them “in check.” Hence, exotic plants have a distinct advantage over the native species. If an exotic species takes hold and extends its range, thus overshadowing or eliminating the native species, the result will be a disruption of the biological interactions. Again, kudzu is an example of an exotic species which has literally taken over miles of terrain because the limiting factors do not exist. Nothing eats it. It does not seem to be susceptible to disease. Therefore, it continues to spread. I have even heard that one southern state has discovered that domestic goats will eat kudzu. This state, taking this factor into account, is experimenting with the idea of renting goats to try to control the progression of this species. An interesting concept but how much can a goat eat, or better yet, how many goats will be needed to slow down this species’ steady migration?

Native species, on the other hand, have the limiting factors in place. They are susceptible to disease and insect damage and consequently, their abilities to invade vast areas are limited. As they have developed complex interactions with other species, they are potential food sources for a variety of birds and animals. As they have evolved in an area over time, they are hardy and can flourish under local environmental conditions whether it is rainfall, pH and soil types, and temperature. Of course, before planting, check on the various environmental factors and match those with the species’ requirements.
Some of the most invasive exotics are Japanese honeysuckle, Japanese barberry, Japanese spirea, plume grass, tree of heaven, oriental bittersweet, and privet. If one does choose to put in exotics, I would suggest refraining from attempting to plant these particular species.

It is important to keep in mind that we are surrounded by exotics, and these exotics are not limited to plants. Fire ants have arrived and are moving north. Some states are contemplating bringing in a predator of the fire ant to control its spread. Such a program may or may not work. Past efforts to control one exotic species with another have not necessarily been effective. Some exotics brought into an area to control another exotic have, in turn, become major problems themselves. In Hawaii, the mongoose was brought in to control the rats, which had arrived on ships. The problem with this “instant fix” was that rats came out at night and the mongoose hunted by day. The mongooses could not control the rat population but they did hunt the nene (Hawaiian state bird) almost to the point of extinction. The nene had no defenses against an exotic, meat-eating predator. The gypsy moth, another exotic species, is destroying acres of forest in the northeast. This species was brought to Hartford, Conn., in the early 1800s as a potential source of silk to be used in the clothing industry. A few escaped. Northern states have spent millions on trying to control its spread with limited success. As far as I know, the only native predator of the gypsy moth caterpillar is the black-billed cuckoo. Although the cuckoo is common in many areas, it can not control the growing spread of this moth.

So, reviewing the pros and cons of using exotic plant species or native types, I hope that you will decide to use native species. Perhaps some exotics may have a greater aesthetic value, but it is important to balance this positive with the potential negatives planting an exotic may have in your area. If you need more information as to what to plant, I would suggest that you contact your local Soil and Water Conservation District, the Botanical Gardens at Asheville 828.252.5190, the North Carolina Botanical Garden 919.962.0522, or your local Cooperative Extension Service Office.

(Jamie Johnston, executive director of the Little Tennessee Watershed Association, wrote this article. He can be reached at LTWA, 5 West Main Street, Franklin, NC, 28734; or via e-mail at nbumppo@dnet.net.)

 

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