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American Society of Landscape Architects


December 2006 Issue


Science has revived one favorite of yesteryear, the American elm. Can it do the same for the American chestnut?

By Marty Carlock

Uncommon Hedges Mark Turner

On a weedy acre-plus plot outside Boston stand 330 tree saplings, their trunks sheltered by collars of aluminum flashing and cylinders of plastic mesh. They’ve been there for four growing seasons. Some are as tall as 15 feet, and most look vigorous. These are American chestnuts, a species destroyed by chestnut blight in the first half of the twentieth century.

In a few years the small trees that survive here will be inoculated with the blight fungus, Cryphonectria parasitica. Some will die. Some won’t because they are scions of cosmopolitan parents, a blend of American chestnut genes with those of the Chinese chestnut, resistant to the disease. If all goes well, descendants of these resistant chestnut trees—and others—may be available to landscape architects within a decade.

Chestnut restoration research lags in the wake of development of disease-resistant American elms, another species almost wiped out by blight—Dutch elm disease, in that case. But there’s a difference, says John Emery, who is in charge of this batch of experimental seedlings. “The chestnut project is more ambitious; it’s an attempt to resuscitate an entire species.”

Elm trees that become blighted can be treated with thiabendazole, a fungicide that must be injected so as to spread throughout the crown of the tree. There is no such medication for chestnuts, which must either fight off the disease on their own or succumb. While treatment is available for elms, trees on the market today are all clones taken from a few trees found to be naturally more or less immune to Dutch elm disease. “It’s a cookie-cutter approach,” Emery points out. “There’s not the diversity.” Even so, those graceful, vase-shaped trees, once thought lost forever, are becoming common again in the nation’s townscapes.

The renascence of the chestnut, by contrast, is based on genetics.

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