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Down in Rock Creek Park, it’s hand-to-hand combat against a green menace.

They seemed friendly enough at first. Originally invited to this country to work in gardens, they now chafe at their marginal roles and are intent on escaping civilization to join up with their companions in the woods. There, they plan to establish a hostile monoculture, where only their own kind can flourish.

The plan is working. They began by stealthily killing off the natives, strangling them and leaving their dying carcasses to rot by the river’s edge. Armed with spikes and garrotes, they drove off the remaining defenseless residents. They want nothing more than to seize every place in the sun.

Sue Salmons wants to stop them. As chief of the non-native invasive plants program in Rock Creek Park, she wages a daily war against “exotic aggressive pest plants,” whose escape from gardens and highway embankments threatens the park’s fundamental identity.

“It’s a real battle to save the ecosystems,” she says early one Thursday morning, standing in a thatch of offending Japanese stilt grass in northern Rock Creek Park. She trains her professional eye and her backpack herbicide sprayer on the bamboolike stuff, drizzling the waist-high plants with a vibrant-blue fluid: “These things increase on an exponential curve, and right now we’re on the really steep part going up.”

It’s a growing battle, which is why she shows up at her base in the Rock Creek Park Maintenance Yard by 5:30 every morning, ready to pump fuel into her Ford Ranger and mix the toxins that will root out the invaders—every leaf and branch of them. Dressed in her olive-green National Park Service jumpsuit and regulation brown forest boots, the onetime organic farmer often walks the two-and-a-half miles to work through the cool and dark of the forest.

At the maintenance yard, she is joined by her bearded, bespectacled assistant, Joe Kish, and his red Kawasaki Mule, an all-terrain off-road vehicle that resembles a souped-up golf cart. By 6:30, they are in the field, targeting four to 15 acres per day of the park’s innumerable non-native hot spots.

It’s lonely work, not least because two staffers and a volunteer in summer make a paltry tactical force against the hordes threatening the park’s 2,700 acres. Even with these hardy few, Rock Creek’s program is one of the National Park Service’s three most intensive non-native extermination programs this side of the Mississippi, a pioneer in researching potential “treatments” to cure non-native plant infestations.

Though the park had been trying to root out kudzu, a fast-growing imported vine that has overtaken much of the South, since the ’70s, it was only in 1996 that the rangers began an intensive herbicidal program targeting a broad array of obnoxious plants. That year, the park received a grant to do a three-year study on treatments for Asian bittersweet and other woody vine infestations. Pilot studies of fire management—controlled high-tech burning—and mechanical management—an advanced form of weeding—suggested that neither approach was particularly helpful.

But the chemical warfare, herbicides in particular, showed promise. “We did 10 treatment plots and 10 control plots,” says Salmons, “and we managed to get over 90 percent mortality from one year to the next….We treated 13 species—all that we could find. Of those, we found effective treatments for 11.” Today, these treatments are the advance soldiers in the war against non-natives. Today, Salmons and Kish are going to show me the front.

The birds are barely chirping when we park the Mule and the pickup along the bank of Wise Road and prepare to head through the forest to today’s target site: an infested plot along the flood plain of Rock Creek. Salmons pulls on her gloves, goggles up, and pours Garlon and Rodeo, herbicides safe for use near water, into her plastic backpack, a milk-jug-white contraption with a leaky valve given to whistling like a distant bird. She and Kish grab the 45-pound red tanks of the potion for restocking later on, and we head down a steep incline. Slender branches grab our clothes, and we have to duck and weave around shrubs and saplings, taking care not to trip over fallen branches or hidden roots. The canopy above us is sparse, and you can see the forest behind the trees.

“This is what an American forest should look like,” Salmons says to me. “See how you can see through the trees?” Healthy mid-Atlantic American forests do not look like the forest primeval, all hung about with ropey vines and creeping leaves. They just look like the woods.

We reach a clearing made up of thin skeletons, a stand of winged euonymous previously infested with Asiatic bittersweet—a “Level-2 threat”—that has been treated. The empty brown vines of bittersweet still cling to trees, and the spindly branches of the euonymous bushes stand naked.

“This is a vine we killed a couple of years ago,” Salmons says pointing to a long trunk arching high above our heads. But as she looks it up and down she notices something unexpected: leaves. “Maybe it’s not dead,” she decides, adding: “We won’t kill that today.”

When rangers started treating this area of the park in 1996, there were vines extending from the road right on down the hill, and the whole area 50 feet back from the creek was a thick tangle of rapacious foliage. About 80 percent is gone now, but when we reach the flood plain it takes just a few minutes to find five of the Top-10 threat plants, plus one Level-3 threat run rampant.

“Vines are not normally a big part of this ecosystem,” Salmons explains. Four out of five of the most aggressive threats to the park are woody vines. Right here, where the creek bends and a co-worker nearly stepped on a displaced beaver mom nursing her pups last spring (she’d been flooded out of her home), the aptly named mile-a-minute vine had grown rampant. Also known as devil’s tear-thumb for its small thorns and trident-shaped leaves, it is an herbaceous rather than a woody vine. But it is as unwelcome as its knotty brethren.

Up the creek, where three toppled trees have created a small island, this member of the polygonum family has covered everything. It looks beautiful in the early-morning sunlight, with its seed pods growing out of a leaflike cup and tumbling triangular foliage. Small insects flit above the mass. But the vine, however lovely, is alien to the landscape around it. And at the river’s bank, there is wild hops, brought over from Europe for making beer, its five-pronged serrated leaves shining. All of it is crowding out what used to be here.

Honeysuckle seems the most familiar of plants, carrying with it memories of childhood summer evenings, each trumpet flower holding its delicate nectar treat. And yet: “All the bush honeysuckles are non-native,” Salmons tells me. “Anything [vinelike] that has white or yellow flowers is non-native.”

American honeysuckle has red flowers. White or yellow-blossomed Japanese honeysuckle, which hangs over Rock Creek’s edge on the Wise Road flood plain in a romantic cascade, is strangling a plant underneath. It’s taking up room that might otherwise be used by a rarer plant: impatiens, which grows by the still water’s edge some 15 feet away, guarding the minnows. Impatiens, the shy, sensitive plant otherwise known as touch-me-not, is much less hardy and more particular than honeysuckle. Its range is limited.

Most problem plants, like English ivy, can be traced to gardens and landscaping efforts. Originally from the Caucasus mountains in Central Asia, English ivy is ubiquitous in landscaping and frequently creeps away from its appointed place. Indeed, one of the first things Al Gore did when he moved into the vice president’s residence is order that the ivy, which had overtaken a considerable expanse of the grounds, be torn out and replaced by native and indigenous species.

Back in her office, Salmons keeps a memento of how bad the problem can get: thick slices of an English ivy vine cleared from the park, with a diameter of 4 inches. It had been growing 18 years.

Pro-recycling gardeners also exacerbate the problem: “A lot of our problem directly in the park is that people dump their garden clippings in the park thinking they’ll just break down. But every piece of woody stem will grow once it hits ground,” says Salmons.

In a city that has a tendency to build monuments to memorialize heritage, Salmon thinks it’s worth the time and effort to defend America’s green legacy. From a car cruising through the park, Rock Creek’s forest looks like any banal stretch of trees by any highway in the area: It’s pretty but unremarkable. But the park actually showcases eastern American plants more fully than the National Arboretum. The arboretum may be picturesque, but the park is the actual American landscape, rugged and rocky and full of unidentifiable crooked trees: the native species whose names we were never taught. There are some 418 native species in the park. Among them are more than 20 species of compound-leaf trees, whose feathery fronds resemble small branches, and at least 12 types of oak. But some 238 non-native species have also been identified, of which 41 are considered aggressive pests.

Having finished with a patch of tear-thumb, Salmons sprays her way farther down the riverbank, clearing out hops and garlic mustard and bittersweet to make room for sedge and compound daisies and a fat yellow grasshopper that has just emerged from hiding. Soon, most of the treated plants will wither and die, sinking back into the flood plain from which they sprang. But some will live to fight again. When they return, Salmons and Kish will be waiting for them. CP