Originally created 09/10/04

Rise and fall of the chestnut tree



James Hill Craddock calls himself a chestnut breeder, but a truer description would be a chestnut evangelist. For the better part of his 44 years he has been preaching the virtue of the genus Castanea.

I think the world would be a better place with more chestnuts," Craddock told Smithsonian magazine for the September issue.

His particular concern is the American chestnut. Once known as the redwood of the East, the tree ruled forests from Georgia to Maine until it was devastated by chestnut blight in the first half of the 20th century. By 1950, the fungus had killed some four billion American chestnut trees"the greatest ecological disaster in North America since the ice age," Craddock says.

Today, the towering American chestnut of old is very rare, and hardly an acre of its natural habitat is blight free. Yet Craddock, a biologist at the University of Tennessee at Chattanooga, persists in his optimistic mission of restoring the vanquished tree. At several experimental orchards outside Chattanooga, he is breeding scores of chestnuts in an effort to develop blight-resistant hybrids that could be planted in forests, helping reestablish what was once, he says, "the dominant tree in the canopy."

The tree once played a critical role in American life in the eastern United States. The nuts that rained down each fall fed nearly all the inhabitants of the forest. The trees grew fast and tall and straight, reaching more than 100 feet high and as much as 9 feet in diameter in 75 to 100 years. The wood resisted rot and warping, making it a favorite for fencing, utility poles and furniture. People built homes from chestnut logs, buried their dead in chestnut coffins and fattened their hogs with the tree's nuts. In Appalachia, the blight dealt a blow as crippling as the Great Depression.

The disease was first observed in 1904 at the Bronx Zoo, and scientists soon determined that it was caused by a fungus that had arrived in America on chestnut trees from Asia. In its native habitat, the fungus, Cryphonectria parasitica, is relatively benign. Asian chestnuts can shrug off an infection, but the American chestnuts quickly succumbed. The fungus, whose spores infiltrate tiny cracks in a tree's bark, can kill a healthy tree in a year.

The blight moved with heartbreaking speed, carried by the wind, animals, insects and humans. Despite efforts to stop the pandemic, "it spread about 30 miles a year in concentric circles from New York City," says Craddock. By 1930 many of the chestnut trees in the forest canopy were dead or reduced to mere shrubs as far south as North Carolina and west to Ohio.

The chestnut trees we see today outside forests are mainly European or Asian species, smaller and less majestic than their American kin. A few mature American chestnuts survive, but they are ravaged by cankers. There are also rare cases of isolated trees that have escaped the blight. And though the forests are full of chestnut saplings sprouting off the root systems of blight-infested trees, their growth is stunted. For decades it was thought that the stately American chestnut was lost to the past. But thanks to Craddock and others, it now may have a future.

Craddock follows breeding procedures championed by corn geneticist Charles Burnham, who helped found the American Chestnut Foundation in the early 1980s. Since that time, the foundation has led the effort to breed blight-resistant hybrids at its experimental farm in Virginia.

In the technique, known as backcrossing, successive generations of Asian-American hybrids are crossed with pure American trees. The idea, Craddock says, is first to transfer blight-resistance characteristics to the American species, then phase out all other Asian traits by subsequent crosses with American chestnuts.

Scientists predict it will take at least five generations of crosses to produce a highly resistant tree. Even so, the odds are daunting: for every hundred trees produced, only a handful acquire resistance.

"If you were a professional gambler," says Craddock, "you'd never bet on the American chestnut tree." Still, the foundation's efforts appear to be paying off: the program expects to have its first blight-resistant nuts ready to test in forests by 2007 or 2008.