English ivy makes up the beautiful canopy that covers Rock Creek Park. The green, waxy vines wind up trees and sprawl across hills. But as the vine grows, it twines tightly around tree trunks, cutting through bark and blocking the trees’ internal flow of water and nutrients.
“We are attacked at every single angle,” said Ana Chuquin, the botanist at National Park Service who oversees the Rock Creek invasive plant removal program.
More than 200 non-native invasive plant species have infiltrated Rock Creek Park, disrupting the ecological balance of the District’s largest green space, said John Maleri, restoration manager at Rock Creek Conservancy.
“Invasive species, as the name suggests, they’re invaders. They are not from this area. They get in here when seeds spread via birds, animals or people. And what they really do is outcompete the native varieties of plants that we want to have growing in this natural area,” Maleri said.
In Rock Creek Park, invasive plants proliferate along roads, trails and waterways. Although some species can grow in the forest shade, many prefer sunlight and are commonly found in sunny areas like the trails along the forest edge.
Invasive species in the park include certain types of trees, vines, shrubs and groundcover plants.
“Sometimes they can grow faster. Sometimes they can grow quicker, and they’re more optimized to grow here. And they don’t have any natural predators. And that can be a problem because they outcompete those native species that provide habitat and food for local wildlife,” Maleri said.
Invasive plants also create problems for native species like owls, woodpeckers and other animals that burrow into dead trees. In areas near Dumbarton Oaks in Georgetown, porcelainberry vines have smothered the vegetation, toppled dead and weak trees and destroyed habitat for cavity-nesting native animals.
Many of the invasive species in the park were brought to the area by people as decorative plants or for food, according to the Conservancy website. Over time, the plants spread to the park, where they outcompete the native species.
Some of the worst invaders in Rock Creek Park are English ivy, bamboo and porcelainberry, per the Conservancy website.
The spread of English ivy has become a major problem in Rock Creek. It covers 19 percent of the park and can be difficult to remove. This highly invasive vine is popular with gardeners, but the vine is difficult to contain.
Once it spreads, the ground cover version carpets the forest floor, preventing native species from growing or accessing sun and nutrients. The vines can also strangle trees and topple them to the ground.
Bamboo is “one of the most problematic species” in Rock Creek Park, according to the Rock Creek Conservancy Watershed blog. Common bamboo, golden bamboo, arrow bamboo and stiltgrass or “little bamboo” are all overgrown in the park.
Little bamboo is a type of grass originally brought to the United States in 1919 as packing material for fine china. It has spread to 16 states and significant portions of Rock Creek. It grows in almost all conditions, which “threatens native understory vegetation in full sun to deep shade,” according to the National Park Service’s official handbook on invasive plant species in the Mid-Atlantic.
Porcelainberry is a “vigorous” invader of open and wooded habitats where it steals sunshine from native shrubs and young trees, according to the park service handbook.
“Despite widespread knowledge of its invasiveness, porcelainberry is still widely sold and planted,” according to the Rock Creek Conservancy’s website. The porcelainberry vine grows commonly in Rock Creek Park and can usually be seen along the forest edge.
Invasive plant removal is only the first step in maintaining a healthy park.
“The work doesn’t finish when you remove invasives, the area needs to be restored,” Chuquin said.
Wesley Cornell, a garden designer who selects plants for restoration projects in the park, agrees.
“It’s going to be an ongoing effort to keep invasives from coming back because this is such a disturbed site that it’s going to take a little while for these natives to, to establish and outcompete invasive plants,” Cornell said.
The aim of the restoration projects is to plant aggressive native species very densely so they stand a chance against the invasive plants. Cornell, as a designer, also said he tries to strike a balance “between what I feel like would do best in the site and colonize very quickly and give aesthetic value to the neighbors.”
“Restoration is important because it allows us to keep our natural areas enjoyable for humans but also for all of the wildlife,” said Maleri, who oversees the plant restoration projects and manages volunteers. “Rock Creek Conservancy is doing a ton to help educate and advocate for these programs in the greater community.”
The Conservancy invites volunteers to participate in monthly invasive plant removals and restoration projects.
Rena Subotnik, the Conservancy’s “Volunteer of the Year,” said that most people probably wouldn’t identify invasive plant species as harmful because some of them are quite beautiful. But, she said, invasive species are doing real harm to the park.
“Most people think green is good, so it’s hard for them to see things that don’t belong. I try to think of it like I were a dermatologist. People see, like, tan as lovely,” Subotnik said. “But if you’re a dermatologist you go ‘blegh.’ It’s invasive what you’re doing to your skin.”