Biodiversity Task Force Focus-on-Habitat Series:
Invasion of the alien plants: Dealing with invasive species

by Pam Owen

	Garlic mustard (Alliaria petiolata). Photo courtesy of the National Park Service.

What plants can truly be considered as"nonnative" in our area? It’s hard to pick a time when all of Virginia's plants were "native," since air and ocean currents, as well as animals and the first humans to settle here, have all introduced species to this area.

However, European settlers sped up the process by bringing many plants (and animals) from their homes with them—for their perceived beauty, for their economic value, or just because they made these people who had traveled so far feel more at home. Modern transportation has further accelerated the process.

The result is that many of our native species are being overwhelmed by these relative newcomers. Nonnatives hitch rides on ships and airplanes when they weren’t being offered a seat onboard by a government agency or commercial firm who thought they’d be beneficial to have here. After all, nonnatives have fed our livestock, perfumed our summer breezes, made our properties look pretty, and helped stabilize erosion that could otherwise erode and pollute our water. So what's the problem?

While some people have argued that these exotic plants are just filling a niche that is available, others warn that this alien invasion threatens native plants and wildlife and the biodiversity they represent. The U.S. Forest Service has published a photo-filled guide to the most common ones that are threatening native forests, Nonnative Invasive Plants of Southern Forests: A Field Guide to Identification and Control, by James H. Miller. In the introduction, Miller explains the impact of invasives on Virginia's forests: "Invasive nonnative plants infest under and beside forest canopies and occupy small forest openings, increasingly eroding forest productivity, hindering forest use and management activities, and degrading diversity and wildlife habitat." The U.S. Forest Service also offers a list of invasives on its website (www.fs.fed.us/database/feis/plants/weed/weedpage.html).

Tree-of-heaven (Ailanthus altissima). Photo courtesy of the National Park Service.

Forest Ecologist James Akerson, who heads of the Exotic Plant Management Team at Shenandoah and eleven other national Parks in the mid-Atlantic area, also sees invasives as a threat to native ecosystems:

"Invasive exotic plants displace native species," he says. "That is a direct impact of one plant squeezing out another. It is also an indirect impact of changing the microenvironment and thus discouraging associate insects, small mammals, bird, and others."

The Park and the National Audubon Society has joined in fighting one exotic invasive that is threatening bird species in what Audubon has designated as the "Upper Blue Ridge Mountains Important Bird Area," which includes the Park.

"Though certain birds may enjoy bittersweet berries, much like kudzu," Akerson explains, "the vine inhibits a host of native plants where it invades. The preferred food chain is harmed." This invader is such a threat to that Audubon has joined with the Park in fighting it.





For more on Important Bird Areas, go to http://iba.audubon.org/iba/viewState.do?state=US-VA.

Along with Oriental bittersweet, the Park is in a pitched battle with mile-a-minute vine, Oriental lady's thumb, Japanese stiltgrass, and garlic mustard, says Akerson. As the Park’s neighbor, Rappahannock County faces the same threats, along with autumn olive, ailanthus ("Tree of Heaven"), multiflora rose, Johnson grass, Asian cattail, Japanese honeysuckle, and others.

	Mile-a-minute vine (Polygonum perfoliatum). Photo courtesy of the National Park Service.

While nonnatives won’t destroy the planet, a less biodiverse planet is a less safe planet for all of us who live on it. When one species—such as a plant that provides us food—fails, biodiversity offers a safety net with other species that can provide similar resources.

Besides, how many of us in Virginia would be happy to see our dogwoods and redbud replaced by ailanthus, or our native wildflowers replaced by garlic mustard? Our sense of place, especially in Rappahannock County, is to a great extent defined by the species that not only share this beautiful landscape but actually create it.

"So, will we ever get rid of these alien invaders?" That's a tricky question, since cutting some species at the wrong time can just spread seeds and encourage growth. Others grow by spreading rhizomes underground, so cutting what is visible aboveground can just encourage more rapid spreading underground.

Japanese stilt grass (Microstegium vimineum). Photo courtesy of the National Park Service.

Even in the Park, which has an active invasive-management program, elimination of all invasives is not a practical goal, according to Akerson. "We do not believe it is practical to consider eliminating all invasives from Shenandoah National Park," he says.

Should we throw in the towel? Not according to Akerson, who explains, "It may be tempting to say, 'With all the trade and travel today, what's the use of attempting invasive species controls?' The problem is that the virtual Pangea created by international trade eliminates the essential niches that separate continents allow for species and habitat diversity. We will lose many hundreds of species without protection of our precious habitats."

The trick is to pick your fights, as Akerson notes. The Park has focused its fight on what it considers its critical areas: "We are committed to protecting natural and cultural areas of high value," says Akerson.

Humans are not alone in the fight against invasives. Nature has its own defensives against species that run amuck. In time, most species develop predators. A rust is already attacking multiflora rose. Some local haters of this prickly species have gone so far as to transplant infected plants from other areas into patches of the species on their properties to help nature along. Of course, trying to "help" nature is partly what has gotten us into this fix to begin with, so this style of warfare has its own potential to create problems.

What can we do to help the spread of invasives?

"At your homes, think beautiful, think native," says Akerson. "Ask your favored nurseries to stock native plants and shrubs. Refer to the Virginia Native Plant Society [http://www.vnps.org/index.htm] for their recommendations of native plants for your region and location."

"At Shenandoah National Park," Akerson adds, "join the Park to strategically control invasive plants. Call the Park’s invasive plant volunteer leader, 540-999-3496, to set up a time for your family or civic group to join others in the effort to protect native plants and their habitats." One such effort is the Park's annual "Save the Meadow!" event at which volunteers can help to control garlic mustard from invading Big Meadows Swamp. This year, the event is May 19–20.

If you have decided to do battle with invasives on your property, you may be facing another problem: What to do with the plants once we cut them down or pull it from the ground. Burning pollutes the air; and composting may help them spread or just not be practical if you have acres of something like autumn olive.

Increasingly, people are coming up with creative ways getting rid of these unwanted species. One man who raised chickens and wanted to tackle honeysuckle on his property in the winter found that chickens enjoyed its green leaves at that time of year, when few other plants were offering beneficial nutrients. Other energy-minded folks are tackling exotics by turning them into electricity by feeding them into biomass-fueled generators. Maybe you can come up with other creative uses.

However, before you start battling invasives, it’s good to get some expertise. To this end, the Rappahannock League for Environmental Protection’s Biodiversity Task Force, as part of its continuing "Focus on Habitat" series, will host a presentation on managing invasive species by Akerson. He will explain how invasives threaten biodiversity, how to identify species that are common in Rappahannock County, and techniques for managing them.

The presentation is Saturday, March 24, 10–11 a.m., at the Rappahannock County Library. Admission is free, but please come early to ensure getting a seat. For more information, call Pam Owen at 540-522-3075, or send email to Biodiversity@RLEP.org.