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"Invasive exotic plants are a threat to forest health and biodiversity," says Joan Ehrenfeld. This project assessed invasive species across thousands of acres in the Highlands region. Researchers, including student Kai Li Tan, above, surveyed 175 miles of hiking trails from New Jersey's Ramapo Mountains to New York's Harriman State Park. The work was funded by the U.S. Department of Agriculture.
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Because there are not enough trained scientists to go around, ecologist Joan Ehrenfeld, center, and her team trained "citizen scientists"—avid recreational hikers—to identify native and invasive species. Joining Ehrenfeld at New Jersey's Wawayanda State Park, graduate student Kristen Ross, left, and undergraduate Alexandre Chausson get ready to retrace the volunteers' steps.
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More than 130 volunteers in teams of two sampled two-mile sections of hiking trails. Later, "validators" like Ross and Chausson—highly trained in plant identification—collected data along the same stretches of trail to assess the volunteers' accuracy.
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Undergraduate Joe Steinfeld checks the identification of Celastrus orbiculatus, or oriental bittersweet, a very common and dangerously invasive vine.
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Bittersweet's thick climbing vines can strangle a tree, its prodigious leaves can block the sunlight from reaching a tree's leaves and prevent photosynthesis, and its growth into treetops can weigh a tree down, making the tree much more likely to topple over in wind and ice storms.
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While U.S. nurseries generally do not sell Celastrus orbiculatus (opting instead for its safe American cousin, Celastrus scandens), it's easy to find non-U.S. sellers touting the vine, like this from the United Kingdom: "A wiry stemmed climber grown mainly for its colourful fruits, which split open in autumn to reveal bright red seeds. Golden autumn foliage. Height to 30 ft. Best up a tree."
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Ehrenfeld, right, an expert in wetland ecology, ecosystems ecology, and urban ecology, teaches undergraduate and graduate ecology courses and serves on several federal and state advisory committees involving water management, wetlands, and invasive species. In April she will present a public talk about the Highlands project at the University of Wisconsin.
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By altering soil chemistry, Japanese barberry (Berberis thunbergii), seen here near the forest floor, reduces the depth of essential litter layers in forests. The litter layer is where bacteria, fungi, worms, insects, and other decomposers eat dead plant matter and create new nutrient-rich soil that plants need to thrive.
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A thorny shrub with bright red berries, Japanese barberry is promoted as an excellent deer repellent and is routinely sold by American nurseries that suggest using it to border a property or garden.
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Ross, above, now employed at the Rutgers/Brooklyn Botanic Garden Center for Urban Restoration Ecology, earned her Ph.D. in 2008, working with Ehrenfeld. In August 2009, Ross, Ehrenfeld, Rebecca Jordan, and colleagues presented the Highlands study results at the Ecological Society of America's 94th Annual Meeting in New Mexico. Ehrenfeld hopes to publish the study results later this year.
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"Finding where invasive exotic plants occur in large forested areas is not easy," says Ehrenfeld. "By training volunteer hikers to identify a dozen of the most important noxious species and to collect real data, we were able to survey over 175 miles of hiking trails in northern New Jersey and adjacent New York and gain a large amount of data that can be used to help manage this problem."
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The study found that volunteers were most successful in correctly noting the absence of invasive plants and in identifying commonly occurring species. After participating in the study, volunteers are more careful about what they plant in their own gardens. For them, a leisurely walk in the woods will likely never be the same.
