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Barberry, Bambi and bugs: The link between Japanese barberry and Lyme disease

The views expressed are those of the author and are not necessarily those of Scientific American.


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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.






Comments 4 Comments

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  1. 1. francescafury 10:34 am 03/30/2011

    The only problem with this article is that it is rather misleading. As a landscape architect, I frequently incorporate Japanese Barberry into designs here in central Texas. However, nobody in my profession OR in the nursery profession would ever use the invasive varieties pictured. We exclusively use the ornamental varieties, which are brightly colored, thornless, and typically of the pygmy sort.

    This is what nurseries carry as well. So, perhaps a little more research would allow you to not make an issue of a distinctly non-issue, or at least to clarify where the actual danger in planting such species is. Not all Barberry is created equal.

    Link to this
  2. 2. SarahH 10:58 am 03/30/2011

    I appreciate the clarification of the different varieties available at nurseries. I have planted a thornless type at a former residence and I hope it isn’t the type that could spread. I was thinking about planting this same variety at my new house. However I still think the point the author is making is valid no matter what the type of barberry when referring to supporting the type of deer tick that causes lyme disease. Since humidity is the issue here, wouldn’t large ferns in the woods cause the same humidity issue that is found with barberries?

    Link to this
  3. 3. ssm1959 3:55 pm 03/30/2011

    Thank you for trying to educate people about this problem. My family and I have been involved in Land management/Habitat restoration for nearly 50 years. Few have our experience in fighting this and other Eurasian invaders. What people do not realize that until deer populations reach 15-20 per mi2 invaders can not take over. For many years when the deer population was low, these species were limited to very small enclaves and consequently were not of much concern. In the mid 1970′s the herd density took off and so did the invaders. We attempted numerous restoration projects to no avail. The native species could not compete. Once we realized that the deer were the unaccounted component of the problem, we (with the help of CWD) instituted a severe harvest protocol. Over the last 4 years more than 100 deer have been removed from 300 acres. Immediately the native species expanded, competing quite effectively against the invasive garbage. We are nowhere near the target herd density but the positive results of even this modest change are evident. Fighting the plants is futile without controlling the deer.

    What else could be done? Education, Education, Education. Oddly the hunting public has been the biggest impediment of late. Unfortunately there persists a scarcity mentality that pervades issues regarding people’s perceptions of the natural world. While this was an appropriate view regarding North American ungulates in the last century, its utility has now run short. The fact is the recuperative power of living systems is far greater that we first imagined. Now we are living on the other side of the sword but the required shift in public perception has yet to be made. The first step is to deconstruct the Disney-esque view of “Bambi”. I love the species and have studied them for years, but if we do not control them, we can look forward to depleted ecosystems and a nation wide CWD epidemic.

    Link to this
  4. 4. scott68williams 9:15 am 03/31/2011

    To francescafury. According to the USDA Plants database, Texas is one of the few states where Japanese barberry has not been reported: http://plants.usda.gov/java/nameSearch?keywordquery=berberis+thunbergii&mode=sciname. So perhaps it is the Texas climate and/or soils that keeps it from becoming invasive, and not the variety.

    SarahH. I am often asked that question, if native species can provide the same conditions. While a fernery may create those conditions, ferns do not provide the same habitat and food for tick hosts like mice and deer. This is what makes it the ecological perfect storm.

    ssm1959. You are correct about the deer issue. Currently, we are crunching 4 years of native regeneration data looking at the combined impacts of invasive control and deer exclusion. Stay tuned.

    Scott Williams

    Link to this

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