Attack of the Vines

January 31, 2009
Insidious species: Flora experts Gwinn, in uniform, and Reynolds, left, help citizen scientists identify invasive plants such as tree of heaven (ailanthus altissimus) and black walnut (juglans nigra), foreground

Insidious species: Flora experts Gwinn, in uniform, and Reynolds, left, help citizen scientists identify invasive plants such as tree of heaven (ailanthus altissimus) and black walnut (juglans nigra), foreground
Jon Gardiner

To her left, about five feet off the trail and partially hidden behind a tree trunk, she spies a sprig of privet. She stops. It's no more than a foot high, a rather unimposing specimen. And yet its presence is disturbing. She pulls out a handheld GPS device and clicks "enter" to mark the spot.

Curry '69 is joined by Jason Gwinn, one of the park's five rangers, and Julie Reynolds, a Mellon Lecturer in writing and biology at Duke. Over the past two years, Gwinn and Reynolds have collaborated on a program called Plant Stalkers—a "citizen science" initiative aimed at getting volunteers out into the woods to help identify and map invasive plant species—like privet—using GPS (global-positioning system) technology. Curry, a retired computer scientist, is here for a training run.

The privet is just the beginning. This trail, barely out of sight of the ranger station, is teeming with invasive plant species. Just as Curry notes the privet, Gwinn points out a thin vine that has begun to wrap around the base of a nearby tree: wisteria. The group takes another few steps forward before he once again points left, this time at several green vines arching overhead: multiflora rose.

The idea for Plant Stalkers emerged from a research-service-learning course that Reynolds has taught for several years, called "Conservation Biology of the Eno River State Park." Each semester, Duke undergraduates meet with park rangers to discuss current research needs. One class conducted a survey of mammal life in the park; another focused on a specific salamander species.

But in the field of conservation biology, scientific survey efforts aimed at monitoring species populations often take years to produce meaningful data. Working on a semester schedule, Reynolds saw a pattern beginning to emerge. "Individual students would come out here and put traps out. But they would see very little." Even if they did occasionally find the creatures they were looking for, it was hard to get a sense of gradual population changes.

So when park rangers suggested tracking invasive plant species that are prevalent in the park, Reynolds realized almost immediately that it was the perfect project for students in her class, but also a way to engage the community in scientific research. "The plants don't move," she says, so observers don't have to chase or trap them. "If you step on them or harm them, it's not a problem." But perhaps most important, they represent a very serious environmental threat.

In a strictly aesthetic sense, many of the invasive species are at least as beautiful as their native counterparts. Privet, for instance, has been imported widely for use in ornamental hedges. Mimosa, another target species, yields soft, pink flowers.

Some of these species have been here for so long that they are often regarded as part of the American landscape. On the trail, Gwinn reaches down and brushes dried leaves away from a small honeysuckle stem. In giving ranger programs, he often asks listeners if this particular species is native. Despite the fact that he identifies it by its full name—Japanese honeysuckle—many people still say yes. "They've grown up picking the flowers and eating the honey off of them," he says. It's hard for them to see the plant as potentially harmful.

But ecologists know better.

Ecosystems comprise complex networks of species large and small, and within these networks, invasive species compete with native plants for resources. As Gwinn, Reynolds, and Curry move on, they note large swaths of Japanese stiltgrass, a long, leafy groundcover that forms almost a carpet along the side of the path. The grass, says Gwinn, "takes over the entire ecosystem," forcing out native plants. "The deer don't like it, so you have more and more deer eating fewer and fewer plants." Other species have other detrimental effects that similarly wend their way up the food chain. 

For a new volunteer, a walk through the forest can be intimidating—there are so many invasive plants!   
In crafting the Plant Stalkers program, Reynolds was conscientious about making the activity accessible for volunteers from a range of backgrounds.

Working with undergraduate students recruited through DukeEngage in the summers of 2007 and 2008, she developed training manuals and videos to post to the Web. Together they narrowed a list of twenty-five invasive species that have been identified within the park's boundaries down to twelve "rank-one" invasives, the most pervasive and harmful of the bunch.

Though the students, who had science backgrounds, were able to search for several species at once, they decided that volunteers should focus on one species at a time to make the activity less intimidating—and to reduce the risk of errors in data collection.

Volunteers, who can borrow a GPS unit from the ranger station or bring their own, fill out a worksheet each time they visit the park. As they identify species, they record their findings on the GPS unit, but also note the latitude and longitude of each finding on their worksheet. For more advanced volunteers, the worksheet also  has spaces for "bonus data" that include numerical ratings that characterize the size and density of the infestation, the habitat where it's located, and the tree cover above.

Once uploaded, this data can be plotted onto a map. Ultimately, Reynolds hopes to use these maps to monitor changes in invasive plant populations over time.

Before Plant Stalkers, the park's primary source of invasive-species data—beyond rangers' day-to-day observations—was a survey of all North Carolina state parks done by the park service in 1990. The survey simply noted whether a particular state park had infestations of each of a list of species, and ranked the infestation on a scale of one to five, without describing specific locations.

In his time at the park, Gwinn has come to know the trails well, and has a good idea of where specific species tend to spread, but when he leaves the park, that institutional knowledge will disappear.

The new data will help the park apply for grants to pay for eradication crews. "If 90 percent of a specific trail is highlighted for invasives," Gwinn says, "that makes an impression." It will also allow park employees to document the success (or failure) of particular eradication strategies.

Of course, Reynolds realizes that not all of the data coming in are going to be completely accurate. While Joan Curry has volunteered for the park in the past, seeks and identifies plants with great deliberation, and, on top of that, is an avid participant in geocaching—a hobby where participants use GPS coordinates and instructions posted online to seek out hidden treasures—not every volunteer is going to be so perfectly suited to the task.

Reynolds is still working out a series of checks to make sure her data are clean. For one, she's comparing each new volunteer's early findings to those of botanists who've walked the same trails. She also asks volunteers to mark down information about time and distance collected by the GPS units to get an idea of how fast they were walking—and, by extension, how carefully they were looking. (The .29-mile loop with Curry takes almost thirty-three minutes, including twenty-three minutes standing still.)

But for many of those out there seeking, she says, the real purpose isn't necessarily data collection. At training sessions that she and Gwinn held in August and September, many of the participants were children, or adults without a strong background in science. She's in the process of talking to local high schools about sending students with community-service requirements her way. And she's also hoping that the park will add a GPS-mapping component to existing programs for elementary-school students.

Good data are nice, but the program's main goals, as she sees it, are to increase science literacy, promote environmental stewardship, and foster a sense of civic engagement.