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Summer 2011

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

August 2, 2011

Killer graffiti: Opening a door to beech bark disease

Memorializing summer love by cutting initials into a tree may seem like a harmless romantic gesture, but knife marks can spell death for a smooth-skinned stately beech. Such an act can set the stage for infection, especially by deadly beech bark disease, or BBD.

Carving into the tree "creates a rough spot in the bark, which gets rougher as the tree grows," says Mark Twery, a researcher with the U.S. Forest Service. "Those rough spots are precisely the places where the beech scale can find a place to shelter and attack the bark."

When the scale (an invasive European insect) sucks sap from the bark, "it actually alters the physiology of the tree, making it susceptible to the fungus that causes BBD," says Twery.

Sometimes a tree can seal off a fungal infection, but the disease tends to kill about half of the mature beech trees once it enters a forest. Only about 1 percent of beech trees are resistant to BBD.

The disease arrived in North America in the 1890s on European beech trees that were planted at the Botanical Gardens in Halifax, Nova Scotia. Since then, BBD has swept across New England, down through New York and Pennsylvania, and has spread as far west as Wisconsin and as far south as the Great Smoky Mountains,"most likely by people moving firewood for camping," says Twery.

While the disease may not have entered the Washington area yet, it might be only a matter of time before local beeches become infected. The biggest threat: people transporting firewood from infested areas back to their city homes, "the same problem," says Twery, "that is causing the spread of emerald ash borer and Asian longhorned beetle," two other exotic insects now threatening to wipe out North America's ash and maple trees.

Source: U.S. Forest Service

Cutting initials into a beech tree can expose the tree to diseases.

To immortalize a romance, some people choose to plant a young tree, rather than knife an old one, such as this beech in the District's Whitehaven Park.