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Fall 2014
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FEATURE
European settlers arrived in the Appalachian Mountains to find them covered by American chestnut and, to a lesser extent, Eastern and Carolina hemlock trees.
Today, chestnut and hemlock trees are suffering due to pests introduced from Asia. Chestnut blight, caused by a bark fungus, has nearly wiped out the above-ground portions of mature American chestnuts, even as the trees' root systems continue to survive underground.
The Eastern hemlock and Carolina hemlock similarly have been devastated by the hemlock woolly adelgid, a small sap-sucking insect.
Virginia Tech faculty, staff, and students are working to bring both species back.
At one point, the American chestnut was the most numerous and often largest tree in eastern forests. However, the chestnut blight, first noticed in 1904, devastated the species.
"All words about the American chestnut are now but an elegy for it," wrote Donald Culrose Peattie in "A Natural History of Trees," first published in 1948. "This once mighty tree, one of the grandest features of our sylva, has gone down like a slaughtered army before a foreign fungus disease, the chestnut blight."
The last several years have seen a flurry of efforts to preserve the genetic material of various chestnut populations. That's been coupled with attempts to breed American chestnuts for resistance to blight, either by finding pure American chestnuts with apparent immunity or, more commonly, cross-breeding with the Chinese chestnut, which has a blight-resistant gene.
The Catawba Sustainability Center is using both approaches. In 2010, 50 pure American chestnut seeds from surviving chestnuts in the Catawba Valley were planted to help maintain the seeds' distinctive genetics.
Then, earlier this spring, the center partnered with the American Chestnut Foundation and Catawba Landcare to establish a breeding orchard. Those regional Catawba chestnuts will be bred to produce a tree that is 15/16ths American chestnut and 1/16th Chinese chestnut.
The resulting mix "should look and act like American chestnut trees" while maintaining resistance to chestnut blight, said Catawba Sustainability Center Manager Josh Nease. "It's a long-term project."
Efforts to control the woolly adelgid and restore hemlock populations will take a similarly long time.
In his natural history of trees, Peattie waxed poetic about hemlocks, which are found along streamsides in rocky ravines.
"Approaching such a noble tree, you think it dark, almost black, because the needles on the upper side are indeed a lustrous deep blue-green," Peattie wrote. "Yet when you lunch on the rock that is almost sure to be found at its feet, or settle your back into the buttresses of the bole and look up under the boughs, their shade seems silvery, since the underside of each needle is whitened by two lines. Soon even talk of the tree itself is silenced by it, and you fall to listening."
Like chestnuts, hemlock trees have fallen prey to a pest from Asia. The adelgid was introduced into the area around Richmond, Virginia, and expanded its range from there. By the 1960s, the adelgid was killing hemlocks and spreading rapidly, especially in the Appalachian Mountains.
Scott Salom, a professor of entomology in the College of Agriculture and Life Sciences, has spent years studying the adelgid and its natural predators in Asia.
"There are two reasons [the adelgid has] been so successful," Salom said. "Eastern hemlock trees, and a smaller species, Carolina hemlock, native to Virginia and North Carolina, are susceptible. Other species of hemlock from western North America and Asia are not. So the trees are susceptible when they become infected. There's no natural resistance, and there are no natural enemies because the adelgid wasn't here before."
Salom has identified two natural predators of the adelgid: a beetle in western North America that he began to study in 1997, and one from Japan that he began studying in 2006. He studied both in quarantine and eventually received permission to release both into eastern forests (the North American beetle in 2003, and the Japanese beetle in 2012).
Both beetle species specialize in eating adelgids and are otherwise considered to have little impact on the environment. The beetles live only in hemlock stands and shouldn't, for example, wind up in local households.
Salom said the Japanese beetle seems to have more potential to make an impact on the hemlock wooly adelgid because the beetle feeds at a higher rate and lays more eggs.
The big question remains: Will the beetles save the hemlock trees?
"We can't say that [they will save the trees], but we can say [the beetles are] establishing and feeding on the adelgids," Salom said. "We see that [they're] having an impact but we can't quantify it yet."