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Saving an American Icon
Page 2

Photo of chestnutsWhen you ask people why they want to bring back the chestnut, you get a variety of answers that distill to one core conviction: It was a remarkable tree. Chestnuts grew quickly, with thick, arrow-straight trunks that topped the canopy at 80 feet or more. They were what ecologists call a keystone species, providing habitat and sustenance for nearly every living thing in their vicinity. The nutritious nuts that dropped each fall fed wild game, livestock, and people. The trees also yielded a wondrous, rot-resistant wood that had an unmatched variety of uses, ranging from fence posts and utility poles to pianos and coffins. Ground into a pulp, the tree gave up valuable tannins that were used to process leather. Such a combination of traits has created fans among both the ecologically and the commercially minded. The tree, they say, would be a wonderful addition to the beleaguered East Coast forests of today. Chestnut trees offer a boon for wildlife, a source of lumber that does not need to be chemically treated, and -- because they grow so rapidly -- an especially effective means of soaking up atmospheric carbon.

The goal of chestnut restoration is driven not only by visions of the future. It also rides on nostalgia for the past. In Appalachia as many as one in four trees was an American chestnut, and the forests are still filled with the remains of the grand old trees -- massive silvery carcasses and yawning stumps that "evoke an eerie feeling of longing for what must have been," as one American Chestnut Foundation member put it.

Chestnuts played a central role in the economy and culture of the Appalachian Mountains. People built their homes of chestnut logs, brewed home remedies from chestnut leaves, and sold the nuts to pay taxes and buy necessities like shoes and school supplies. As subsistence farming disappeared after World War I, the tree became a symbol of that vanished way of life. "If ever there was a place defined by a tree, it was Appalachia," folklorist Charlotte Ross of Appalachia State University in Boone, North Carolina, told members of the Chestnut Foundation at their 2004 annual meeting. "It was our icon. We loved that tree."

Love for the tree (some call it chestnut fever) has gone a long way in keeping its prospects alive. That fever has propelled enthusiastic amateurs to tenderly nurse ailing trees, to scour the woods for flowering sprouts, to climb high into trees to pollinate flowers or collect the precious nuts.

One way to outwit the blight is by breeding a tree that resists it. At first, experts considered that a straightforward task. The fungus, Cryphonectria parasitica, originated in Asia. Over millennia, the chestnut trees in China and Japan evolved genes that allow them to live with their parasite. They're not immune, but they don't succumb. By crossing American trees with their Asian cousins, breeders hoped to transfer the genes that would allow the American species to put up a winning fight.

Unfortunately, Chinese and Japanese chestnuts tend to be shorter. As scientists for the U.S. Department of Agriculture (USDA)discovered when they started breeding hybrids in the 1930s, many more genes than the few that govern resistance also cross over. Initially the hybrids grew like gangbusters and appeared to resist the blight. But when they stopped growing after a few decades, the USDA scientists realized they had a problem. The trees were only 50 to 60 feet tall.

Hopes for the tree seemed stymied by a Catch-22: Blight-resistant trees require Asian genes, yet Asian genes produce a tree with neither the height nor the hardiness to survive the fierce forest competition for sunlight. In 1960 the USDA shut down its chestnut-breeding program and the tree seemed consigned to oblivion.

A retired plant geneticist named Charles Burnham became interested in the chestnut's plight two decades after the USDA program ended. He concluded that the breeders had made a basic mistake in crossing Chinese-American hybrids with Chinese trees in order to boost resistance. Any geneticist could have told them the trees would end up looking Chinese.

Burnham proposed an alternative method called backcross breeding, which is used when breeders want to tinker with only a single trait, like susceptibility to disease. A backcross breeding program would start by mating Chinese and American trees. But then, instead of mating those hybrids with Chinese trees, they would be crossed with American chestnuts in order to beef up the quotient of American genes while diluting the concentration of Chinese traits. Ideally, after several generations, the only Chinese genes that remained would be those conferring blight resistance. The result, Burnham dared to hope, would be a tree that looks and grows like an American chestnut but fights blight like a Chinese.

In 1983 Burnham, along with chestnut breeder Philip Rutter and several others, established the American Chestnut Foundation to carry out the new breeding program. The group has grown steadily over the years and now numbers some 5,600 members -- most of them enthusiastic laypeople -- with chapters in 13 states spanning the tree's historic range. But the foundation's center of gravity is the research farm in Meadowview, Virginia, where for the past 17 years Fred Hebard has overseen the day-to-day execution of what he calls "the Burnham hypothesis."

Hebard is tall and lean and has the taciturn, low-key manner of a farmer -- a farmer whose "I reckons" are followed by terms like "phenotype" and "homozygote" and "pyramiding genes." At 57, he has spent most of his adult life thinking about chestnuts. He got hooked on the tree when he was 22, after dropping out of college to work on a dairy farm in Connecticut. He was helping round up stray heifers when he came across an old chestnut sprout. The farmer told him about the blight and all the trees that had died. Something about the story captivated Hebard. "I don't understand the psychology very well, but it gives me a mission."

In 1989, after getting a master's degree in botany and a Ph.D. in plant pathology, Hebard heard that the recently established American Chestnut Foundation was looking for someone to manage its farm. He leaped at the chance, though the job then paid a meager $12,000 and meant moving his wife and two small children to the hamlet of Meadowview. His first year on the job, he planted the open pasture behind the farmhouse with 250 young Chinese and hybrid trees. Since then it's been a long, slow slog: planning matches, planting nuts, collecting pollen, pollinating trees, harvesting nuts, testing young hybrids for resistance, culling inferior specimens.

It wasn't until the mid-1990s that Hebard got confirmation that the plan could even work. He inoculated a group of second-generation hybrids with the blight fungus and then methodically tracked how well each tree coped. Crawling along the ground between the long rows of trees, ruler in hand, he measured the cankers on each tree and compared them to those on the Chinese trees. Gradually he realized that some of the hybrids were showing a marked resistance to the blight. "It looked like the Burnham hypothesis had at least passed its first test," he says, adding with characteristic understatement, "I was pretty pleased about that."

The results also underscored the intimidatingly long odds of creating a fully blight-resistant tree. By tracking how many of those hybrids held up against the blight, Hebard was able to confirm that, as suspected, only two or three main genes control resistance. This means that after all the necessary crosses and backcrosses, only a fraction of the trees he produces will have the level of resistance needed to survive in forests riddled with blight.

When the foundation was started, Burnham, Rutter, and their colleagues thought it would be 2030 before they reached their goal of a truly blight-resistant tree. Hebard now hopes that by 2008 he'll be producing seeds for trees that could be set in the forests, fully equipped to tackle the blight. Even then, he says, "things could go FUBAR [f ***ed up beyond all recognition]." The resistance itself may not be sufficient. The fungus could mutate. New enemies could appear. The trees could be munched up by deer, crippled by gall wasps, or done in by a deadly root rot that is endemic at lower elevations. Residual Chinese genes could yet prevent the trees from getting tall enough to shoot past their competitors.

As far as Hebard is concerned, the ultimate test of Burnham's hypothesis is decades down the line: "The trees look strongly American. Whether that translates into growing like an American, we'll see."

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Photo: Forrest MacCormack

OnEarth. Spring 2006
Copyright 2006 by the Natural Resources Defense Council