Invaders Among Us

They thrive in the Great Smoky Mountains National Park, and they flourish in the Pisgah National Forest in North Carolina. They relentlessly expand across the Cherokee National Forest in Tennessee, and the George Washington and Jefferson National Forest in Virginia, West Virginia, and Kentucky. And, to be blunt, they’re not only rapidly increasing in our national forests and other public lands but also very likely in your suburban backyard or your back 40 in the mountains.

The they I’m referring to are invasive plants, and these non-natives are negatively impacting the indigenous flora and fauna in our region. Joe Cotner, an area forester for the Virginia Department of Forestry, is very familiar with the problem.

“The Southern Appalachians definitely have an invasive plant problem,” he says. “One of the worst is the tree of heaven (also known as ailanthus, paradise tree, or stinkwood), which seems to be just about everywhere. One of the biggest problems with stinkwood is that if you merely cut it down, that just stimulates it to send out more shoots which turn into trees.

“Another really bad one is multiflora rose. Birds eat the fruits (also known as hips) and spread the seeds through their droppings. One of the things that makes this plant such a threat is that it forms deep hedges where other plants can’t live. These areas are so thick that they’re hard for humans to walk through – the briers are quite sharp, too. So, people find it really hard to enter into a multiflora patch and treat it with herbicides,” Cotner said.

But if the multiflora rose is providing food to birds and creating cover for animals, aren’t those good qualities? Not really, Cotner said, because this invasive is doing so at the expense of native flora and the animals which evolved to live among them. What’s more, many invasive plants flaunt other harmful traits.

For example, kudzu and ailanthus both emit chemicals that negatively impact native plants. Kudzu, which has been described “as the plant that ate the South,” was originally introduced as a way to stabilize soil where erosion occurs. But it just doesn’t crowd out native trees and plants. It has even been linked to increasing ozone pollution as it is reputed to change the air and soil’s nitrogen cycle. Tree of heaven creates a different set of problems. The roots secrete a chemical that is poisonous to native flora, further aiding it in forming monoculture stands of trees. 

Another major problem, Cotner said, is Chinese silvergrass, which is a densely bunched grass that can tower to an astounding 12-feet and can take over forest edges and old fields, especially if they have been recently disturbed. When that occurs, says the forester, silvergrass can easily outcompete native plants.

Oriental bittersweet has the same capability. Cotner says this invasive can twine its way up just about anything, its vice-like vines choking the life out of even once hardy, mature trees. The reddish-orange berries are visible during the winter months, and songbirds spread the highly viable seeds within the fruits. “It’s amazing how quickly bittersweet can take over a grove of trees,” Cotner said.

One of the worst invasive shrubs on the Southwest Virginia rural property where my wife and I live is the autumn olive. Virginia Game Department wildlife biologist Dan Lovelace once told me that he began his long career decades ago planting autumn olive as an erosion control, but is now ending his tenure trying to remove this shrub.

“The Virginia DOF used to sell autumn olive,” Cotner said. “Now we know that it can really take over an area and form a monoculture. It’s another shrub where songbirds can easily spread the seeds by ingesting berries.”

Yet another plant that Cotner lists as a threat is sericea lespedeza. On my land, I planted a logging road with clover in order to benefit wildlife. Shortly after creating the travel way, sericea invaded one entire section, its grassy, wavy fronds choking every other plant in its path.

Kevin Kyle, a silviculturist for the George Washington and Jefferson, agrees with Cotner about the threat that these invasives present and adds several more to this rogue’s gallery.

“One of the worst in our national forests is an annual - mile-a-minute,” he says. “It’s a thorny vine that grows very rapidly and shades out the trees and shrubs that it covers. It will blanket the forest floor, too. This invasive also produces lots of seeds that can be viable for up to six years in the soil bank.”

The silviculturist emphasizes that mile-a-minute (which has small, heart-shaped leaves and blue berries) comes by its name honestly, as it can grow six inches daily under the right conditions. What’s more, it’s extremely hard to eradicate because all that stored seed in the soil easily germinates and grows rapidly the next spring.

“The United States Forest Service has been experimenting with heavy duty propane torches to control mile-a-minute in places where it’s really bad,” Kyle said. “The goal is to have the fire consume the leaf litter and destroy the seeds. We’re monitoring this process very carefully and will tweak it in the future if necessary.”

Kyle adds royal paulownia, or princess tree, to the list of worst Southern Appalachian invasives. One paulownia tree can produce many millions of seeds, and this flora can also produce new trees from root sprouts. It can be identified by its lavender blooms and heart-shaped leaves which sometimes run 16 inches in length. Other invasive plants that Kyle and Cotner list as problematic include fescue, Japanese barberry, bush honeysuckle, and garlic mustard, just to name a few.

Controlling Invasive Plants

Invasive plants could be removed organically by simply pulling or digging them, or cutting them down with an axe or chainsaw. However, the only one I have encountered that is easy to eradicate is garlic mustard. The plant’s shallow root system lends itself to easy removal, especially after a rain. I tried cutting down ailanthus trees and all that did was stimulate the roots to send out scores of new trees.

Kyle says that trees such as ailanthus and paulownia can be removed with what is known as basil bark treatment. Combine vegetable oil with herbicide and spray, and completely coat the lower 18 inches of a tree. The vegetable oil helps to facilitate the herbicide’s introduction into the bark.

Kyle said landowners can kill a larger invasive tree with the hack and squirt method. Use an axe to create little “cups” around the diameter, then squirt herbicide into the cups. I also have experienced success, especially with ailanthus trees of all sizes, with the cut-and-spray technique. I sever the tree at its base, then spray the base with triclopyr.

“I would suggest that the public strictly follow labeling instructions, which is the law of course, for these applications,” Kyle said. “We typically use glyphosate and imazapyr for those injections.”

For plants such as sericea lespedeza and fescue, I use herbicide with glyphosate. I especially like to target sericea in late summer right before it produces seeds. Of course, some folks may not feel that they have the skills or knowledge to perform these tasks. And there’s also the fear of mistakenly killing native plants as collateral damage. If this is the case, both Cotner and Kyle suggest contacting your local department of forestry, department of agriculture, extension office, or a certified professional forester.

Can we totally eliminate invasive plants from our region or even our backyards or rural properties? Not likely, Cotner said.

“Landowners probably won’t be able to eradicate all of these plants,” he said. “My usual goal is to help a landowner get to where he can manage his invasive plant problem. In the spring and one or two other times of the year, I like to help folks develop strategies for reducing their invasive plants. That’s what counts as a victory nowadays.”