Largest chestnut in Greenbrier, 1935. (Courtesy of Great Smoky Mountains National Park Archives)

Bruce Beehler is a naturalist and author of 14 books, including the forthcoming "Flight of the Godwit."

This fall I went hiking out on Sugarloaf Mountain, about 30 miles northwest of D.C. Parking near the base, I came upon an experimental planting of American chestnut trees. Then, hiking up the mountain, I found an American chestnut sapling in the forest proper. This was a sprout sent up from old chestnut rootstock that survived underground after the parent tree was felled many decades earlier by the chestnut blight fungus: Cryphonectria parasitica. The sapling I encountered looked healthy and sported a full complement of handsome serrated leaves that were just beginning to turn their glowing autumnal yellow. But this treelet was too small to produce the delicious nuts memorialized in Nat King Cole's "Christmas Song." Such regrowth saplings are killed by the blight before they reach reproductive age.

Encountering this young chestnut made me wonder about science's effort to bring back "America's tree." The world's nine species of chestnuts range from Europe and North America to East Asia. The pathogen that killed off the American chestnut arrived in New York City before 1900, carried on Japanese chestnut saplings imported by horticulturalists for commercial sale. The blight spread inexorably through America's eastern forests, a natural catastrophe peaking during the Great Depression, when nothing seemed to be going America's way. By mid-century, nearly every one of the 4 billion mature American chestnut trees in existence had fallen to the ground. Their rootstock, hiding underground, lingered, like unseen ghosts, but the species was functionally extinct. The United States had lost its most valuable deciduous forest tree.

Before the blight, the American chestnut was the dominant tree in hardwood forests from Maine to Missouri and Mississippi. A mature tree in a favorable location in a well-watered upland valley of the southern Appalachians could grow over 100 feet tall, with a handsome, thick-barked trunk four or more feet in diameter and a spreading crown of rich green leaves that in spring displayed an abundance of male catkins, bearing fragrant white flowers. Every autumn, such a mature tree would produce a crop of several thousand tasty nuts. The species also offered timber for house construction, furniture, flooring, paneling, shingles, fence rails, boxes and barrels. Unlike oak, the wood was light and easy to work. It was also rot-resistant and thus long-lasting. Moreover, the timber made good paper pulp, and its bark possessed a valuable extract used to tan leather.

Historically, the chestnut's abundant nut crop was an important source of nutrition for rural families throughout the east (as it had been for the eastern woodland Native Americans). Hogs and cattle were fattened on nuts in autumn. Even today, thousands of local places's names include the word chestnut to remind us of the overwhelming importance of this species to our culture. The chestnut also was fundamental to the eastern forest ecosystem, its autumn mast feeding white-tailed deer, black bears, eastern gray squirrels, fox squirrels, passenger pigeons and wild turkeys. The loss of the chestnut meant fewer game-rich meals for rural subsistence communities.

From almost the moment the blight began, efforts were made to defeat it -- first to save those billions of standing American chestnuts under dire threat, then to restore the species to its rightful place in our forest lands. Arborists and plant scientists have been carrying out selective breeding and hybridization using various chestnut species since the 1920s to create a blight-resistant American chestnut. The American Chestnut Foundation was founded in 1983 to expand this effort. And yet, a century of effort to breed a disease-resistant chestnut using traditional methods has stubbornly remained a work in progress.

Enter the cutting-edge science of genetic modification. Molecular research teams have devoted decades to creating a transgenic American chestnut. This required first identifying how the fungus attacks the chestnut's biochemistry and then searching for genes from other plants that might block that biochemical attack. Their latest creation, Darling 58, includes a wheat gene that encodes for oxalate oxidase, which denatures the main biochemical threat from the blight: oxalic acid. In a world of blight, no American chestnut can survive without the help of one or more foreign genes.

Genetically modified organisms are controversial in a way that selective breeding -- which is a kind of analog genetic modification -- is not. Groups that oppose the release into nature of GMOs say such lineages might pose a threat to our forests, via the uncontrolled spread of introduced genes, and prevent the world from ever having an "authentic" or "pure" American chestnut. The debate between the pro- and anti-GMO camps is long-standing. However, whatever tools are used to create a blight-resistant chestnut -- GMO or traditional -- the new lineage will include genes from other species and will not be a "pure" American chestnut. Moreover, traditional breeding can produce its own unwanted genetic outcomes that harm a lineage's long-term viability.

Molecular biologists at the Smithsonian Institution tell me that GMO technology is the credible route to getting the American chestnut, or something that looks and tastes like an American chestnut, back into our woodlands. (One colleague rhetorically asked: "Would naysayers object to a GM fix for a deadly disease in humans?"). A genetically modified chestnut offers us a rare opportunity to repair a terrible environment loss.

Approval for experimental release of a GMO chestnut into the wild must be granted by the Environmental Protection Agency and the Agriculture Department. Progress toward that end, however, has recently been roiled by a lab error that led to the distribution of an inferior GMO lineage, which caused the American Chestnut Foundation to withdraw its support of the gene-modifying effort involving the Darling strain, currently the most promising genotype. Scientists supportive of the molecular effort say the Darling 58 chestnut is a good start but that more genetic modification, crossing, planting and field-testing will be required to produce a diverse suite of chestnut genotypes that can prosper in the varying environmental conditions across the species' wide range.

Regardless, once a series of disease-resistant and hearty genetically modified American chestnut lines has been cleared for release, the real challenge will be to get these trees onto the landscape. Decades will be required to reseed our forests. But, no doubt, the GMO route will be substantially faster than that offered by the traditional methodology.

We may think we know what a "natural" eastern forest looks like, but the woodlands we see today are shaped by the population declines of the chestnut, American elm, white ash, eastern hemlock and American beech -- all the result of exotic pathogens introduced unwittingly by humans. As an important first step to restoring our eastern forests, bringing the American chestnut back -- or something as close to it as we can -- is a task worth undertaking. Federal agencies should expand their investment in this groundbreaking enterprise. A successful reintroduction will pay rich dividends. I hope my granddaughter Zadie will be able collect and roast chestnuts from Sugarloaf Mountain's forest by the time she has grandchildren of her own.