National park in lengthy battle with invasive plants

Jake Hughes

FRONT ROYAL — Tackling invasive pest plants is “a long-term proposition,” according to Jake Hughes, lead biological science technician at Shenandoah National Park.

On a rainy and slightly cool Thursday evening, Hughes engaged an audience of around 20 residents in a lively discussion on invasive plants at the Samuels Library in Front Royal.

This talk is the latest in a series of lectures that Friends of Samuels Library has hosted since February.

For better or worse, invasive and non-native plants have become something of a norm for Hughes and park staff. To date, Hughes said the park has documented 352 non-native plant species within its own boundaries and is looking to guard it against future threats.

While most of the non-native species the park has documented are not invasive, Hughes centered his presentation on the handful of pest species that are harming the local ecology.

Such species include garlic mustard, an edible biennial that was intentionally “introduced as a pot herb” back as early as the 1860s.

“We have this invasive species in probably upwards of 50 percent of the park,” Hughes said. “I’m talking 100,000 acres containing garlic mustard plants.”

Although it is not as destructive as the highly resilient mile-a-minute weed, Hughes explained that it can hinder native plants and disrupt animals such as the West Virginia white, a butterfly species rare to Virginia.

Hughes explained that adult West Virginia whites feed on and lays its eggs on cutleaf toothwort, a plant in the same family and “chemically similar” to garlic mustard.

Unlike the cutleaf, West Virginia white caterpillars cannot digest garlic mustard tissue. Hughes said the caterpillars “generally end up dying” as a result.

While running through the pesky nature of garlic mustard and mile-a-minute weeds, Hughes fielded questions. Most were directed at eliminating these pests. One of the more popular methods discussed was using goats to  eat plants like the mile-a-minute.

“Goats are a big, popular control technique,” Hughes said. “They eat everything; they’re like four-legged lawnmowers.”

While he noted that goats are effective in certain cases, Hughes also said that he has never heard of goats being used on more destructive plants like the oriental bittersweet.

Hughes described the bittersweet as a “twining vine” that can “wrap around trees, grow radially and cut into tree trunks” and take over tree canopies.

With bittersweet, the difficulty in eradicating it is partially due to its seemingly never-ending root system.

“You can cut the stem at the soil surface and apply an herbicide right to the cut stem,” Hughes said, which can cut down on sprouting a little bit.

Some herbicides can cause even more damage and end up “killing everything” except for bittersweet, Hughes added.

On top of that, Hughes also pointed out that simply cutting bittersweet stems results in more vine growth.

“I think everyone who has ever tried it, including me, has given up,” Hughes added. “You cut one vine, and you comeback and there are 10 more.”

Bittersweet is also not the only invasive threat without a simple, magic-bullet management technique.

Between physical labor, chemical methods and more complicated environmental approaches, Hughes expressed that anyone looking to tackle invasive pests should “expect it to take a while.”

One of the manual methods Hughes discussed includes the cutting of annual plants and “biennials like garlic mustard” or Japanese stiltgrass “right before its early flowering.”

Even then, Hughes noted that cutting certain species can be a constant process over many years.

“One of the most effective means of controlling invasive is getting some competitive native species growing,” Hughes said, citing bluestem grass as  an example of a plant that can work against many threats.

For Hughes and the limited staff at Shenandoah National Park, the problem of invasive plants are not limited to the few pests discussed on Thursday.

“All indications are that this problem is going to become worse with climate change,” Hughes said. “Some of these species grow better in carbon dioxide-rich environments.”

Despite the growing numbers of invasive threats, Hughes expressed optimism in the high-priority pockets of land the park focuses on for invasive species.

Hughes pointed out that the park was successful with an invasion of Japanese stiltgrass near Limberlost Trail.

Using mostly “grass-specific herbicide application,” Hughes said park staff was able to scale back the stiltgrass over a period of five years. There is now more native grass in that habitat, with the park looking to plant even more.

“In these special habitats and high-priority sites … we can really make a difference,” Hughes said. “There are successes and rewards to it.”

Friends of the Samuels Library will host its next environmental talk on June 11 when representatives from the Shenandoah National Park will present its annual ecology report card.

Contact staff writer Kevin Green at 540-465-5137 ext. 155, or kgreen@nvdaily.com