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The Downside of Deer
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by Marc Imlay | 2011

Forested environments help our mental and physical health, scientific evidence shows. Spending time in the forest generates more comfortable and calmer feelings than spending time in an urban environment. People who live in urban areas and find their lives filled with daily stress can benefit psychologically by spending time in nature. Studies have shown that walking as little as three hours a week benefits the physical health of people with sedentary lifestyles.

The Downside of Deer

 

By Marc Imlay—Forested environments help our mental and physical health, scientific evidence shows. Spending time in the forest generates more comfortable and calmer feelings than spending time in an urban environment.  People who live in urban areas and find their lives filled with daily stress can benefit psychologically by spending time in nature.  Studies have shown that walking as little as three hours a week benefits the physical health of people with sedentary lifestyles.

Enjoying the outdoors and the beauty of nature implies some risks. Potential hazards are present in all the world’s wilderness areas. If you are to enjoy nature safely, it’s always a good idea to get informed about all the local possible dangers such as animals, plants, pathogens, rip tides, geological threats (e.g. volcanic and tectonic activity)—and Lyme Disease.

 

Deer and Lyme Disease

Lyme Disease is the most commonly reported tick-borne disease in the United States. Maryland and Northern Virginia, as well as most of New England, are home to the highest rates of infection. Confirmed cases of Lyme Disease have doubled in Maryland in the past ten years, and it affects people more frequently in their backyards than in the woods. The disease is carried by deer ticks, and numerous studies have shown that abundance and distribution of deer ticks are correlated with deer densities. In other words, the more deer present in a given area, the more ticks you are likely to have. In about half the studies I read, when deer density was reduced to natural population densities, the risk of Lyme Disease was greatly reduced, even to less than 10% of previous risk and incidence. Thus, deer population management is an important tool in any long-term strategy to reduce human incidences of Lyme Disease.

With the extirpation of the cougar and wolf in Maryland and limited predation by coyotes, it is essential to have managed hunts to reduce deer to pre-settlement density of 10-20 per square mile instead of current densities, typically 60-110 deer/square mile. Scott Bates,  regional National Park Service wildlife biologist who coordinates the deer surveys, estimated that Greenbelt National Park has around 101 deer per square mile or 120 deer in the area surveyed.  Hunting restrictions could include number and selection of hunters, bow hunting or archery, timing and location.

 

Deer and land degradation

Deer cause other significant negative impacts, including agricultural damage, and deer-vehicle collisions  have doubled in the past eight years. “Deer can have devastating effects upon the few examples of undisturbed native ecosystems in the state, which remain as small pockets within Maryland’s fragmented suburban and agricultural landscapes. . .” a Maryland Department of Natural Resources report pointed out.  Thus DNR’s goal would be that a maximum of about 20 deer per square mile be maintained, with some natural fluctuation in drought or cold years. More specific determinations can be based on actual browse levels, deer health, and effects on diversity of rare lilies and orchids and percent of deer mice harboring Lyme Disease.

At greatly reduced densities, deer naturally select for certain species and maintain biodiversity. But heavily used deer trails cause disturbance and enable exotic species, such as Japanese stilt grass wavyleaf basketgrass, and Japanese barberry to colonize disturbed habitat deep in the woods.  Integrating aggressive deer population control measures into land management programs is necessary to restore our forests. Surveys of deer density are critical to determine where deer need to be controlled and restoration activities timed for  effectiveness. Deer density is often measured in various ways. such as by noting the presence or absence of greenbrier leaves at the browse level as well as by aerial photography.

 

Japanese barberry and Lyme Disease

There is a 5 to 8.8 times increased risk of Lyme Disease in Japanese barberry dominated areas.  University of Connecticut researcher Jeff Ward reported in 2007 that ticks doubled in Connecticut where Japanese barberry was present. A year later, the  Connecticut researchers found that questing adult ticks were most abundant in areas dominated by Japanese barberry, and that about 44% of the ticks found in barberry were infected with Borrelia burgdorferi,  the spirochete causative agent of human Lyme Disease.  However, only 10% of the less abundant ticks from non-barberry areas were infected. These findings suggest a great probability of humans becoming infected with Lyme Disease in barberry-dominated areas.  Thus, there is an 8.8 times greater risk in Japanese barberry patches. Follow-up studies at other sites found 5 times greater risk in Japanese barberry patches.

University of Missouri research found that Asiatic bush honeysuckle increases the risk of tick- borne disease by a factor of ten. I am so glad we got 80% of the massive populations of bush honeysuckle so far out of Little Paint Branch Park in Beltsville, and Magruder Park in Hyattsville, and all of the massive population out of Cherry Hill Park in College Park.  It had just started in Swann Park in Charles County,  when we then eradicated it. I am also glad we got 99% of the massive populations of Japanese barberry out of Little Paint Branch Park, Chapman State Park and Swann Park.  n

 

Marc Imlay, PhD, is a conservation biologist and chairs the Maryland Chapter’s Biodiversity and Habitat Stewardship Committee.

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