If you type "Japanese barberry" into a search engine, the first result will likely be a National Park Service Web page designed to look like a "Wanted" poster. "LEAST WANTED" is written across the top. It’s a fact sheet about the ecological threat posed by this invasive shrub.
Add the word "buy" to your search, and you’ll find hundreds of nurseries, home gardeners and seed purveyors willing to send a Japanese barberry direct to you. A bit of a contradiction—but a common contradiction in the world of invasive-species research.
"There’s a responsibility for nurseries to educate their staff about invasive species," says Jess Murray Toro, co-owner of Native Habitat Restoration and a former conservation program manager for the Nature Conservancy, "and a certain responsibility when it comes to buying invasive species, whether it’s an exotic fish that outgrows a tank and gets dumped somewhere, or replacing one burning-bush hedge with another."
Japanese barberry (Berberis thunbergii) is a case in point. The spiny, red-berried shrub is designated invasive in 20 states and the District of Columbia. Still, you can probably buy one around the corner. "Plenty more states have it as a problem but they don’t have a council to designate it," adds Toro.
Barberry is hearty. It’s shade tolerant, drought resistant and highly adaptable. It grows in open fields, wooded areas, wetlands and disturbed habitats. It prefers full sun but will flower and bear its oval berries even in heavy shade. It can live in a swamp or a parking lot. It produces many seeds, and germination rates have been estimated as high as 90 percent. Birds and small animals deposit it. Hikers move it from place to place in boot treads. It can grow pretty much anywhere. And it does.
Japanese barberry took a circuitous route to arrive on our shores. An Asian native, it was introduced to the U.S. as an ornamental in 1875 when seeds were shipped from St. Petersburg to Boston’s Arnold Arboretum. For over a hundred years, while it’s been gussying up neighborhoods, it’s also been escaping from cultivation. It’s taken over turf from Northern Quebec to Georgia and moved as far west as Wyoming. Native plants and wildlife have lost habitat. Soil chemistry has been affected.
And here’s the kicker for those of you who’d still consider planting it in your backyard: The prevalence of ticks infected with the Lyme disease–causing spirochete (Borrelia burgdorferi) is greater in areas with Japanese barberry than areas without.
"Deer eat everything but barberry, and because they don’t eat barberry, they’re weeding out forests. They’re helping promote the invasive species," explains Jeff Ward, chief scientist for the Department of Forestry and Horticulture at the Connecticut Agricultural Experiment Station (CAES).
Thanks to Bambi’s distaste for its harsh chemicals and spiny branches, Japanese barberry is left alone to thrive while other plants such as red trillium get shaded out or nibbled to the ground.
Japanese barberry has denser foliage than most native species. As a result, the plants retain higher humidity levels. Ticks need humidity and become desiccated when levels drop below 80 percent. Relative humidity under a barberry is about 100 percent at night.
"The plant exists in an umbrella-like form, so the daytime humidity drop is much more subtle under the canopy of barberry than under other plants," says Scott Williams, a research scientist at CAES. The shrubs also provide nesting areas for white-footed mice and other rodents, which are primary sources for larval ticks’ first blood meal, and reservoirs for Borrelia burgdorferi.
In the open, ticks can only be active for 15-16 hours per day, but when they’re protected by Japanese barberry, that number increases to 23 or 24. "There’s only an hour or two when they would have to retreat into the soil," Williams explains. "Instead, they sit and hang out and wait for a host like you or me or a raccoon." Since the majority of Lyme disease cases occur from nymphal tick bites, and nymphs are most active in the summer, risk is highest during the warm months when we’re all happily tromping around wearing shorts and sandals. In forests. In backyards. In parking lots. Day and night.
The message is clear, and pretty obvious: Invasive species affect our lives and our environment—as well as our economy—in a multitude of ways both direct and indirect. But are people paying attention?
Williams concludes: "The majority of people think plants are green and they’re out in the woods. But we’ve documented factually that, indirectly, this invasive plant can have a negative effect on human health. When you start telling people that this plant can negatively affect them, their pets, their children, then they start paying attention."
It’s April. Time to get moving on the barberry removal.
Image credits: Japanese barberry infestation, Steve Manning, Invasive Plant Control, Bugwood.org; life cycle of deer/blacklegged tick courtesy of USDA; Japanese barberry photo, Jil M. Swearingen, U.S. National Park Service, Center for Urban Ecology, Washington, D.C.; Japanese barberry infestation in Sheffield, Mass., Native Habitat Restoration, 2010.
Here are two more photos of Japanese barberry infestation. These are from Sheffield, Mass., showing the same forest before (top) and after (bottom) the infestation. Credit: Native Habitat Restoration, 2010.
About the author: Beth Jones is a journalist, author, blogger and educator who has contributed to the Boston Globe, New York Times, Huffington Post, public radio stations in Massachusetts and New Hampshire, and numerous magazines and academic journals. She is a co-author of the book Three Wishes (Little, Brown & Co., April 2010). Her nonscientific Web site is www.Beth-Jones.com
The views expressed are those of the author and are not necessarily those of Scientific American.