Reviving the Chestnut Tree

In the warm summer months, the mountains of Appalachia used to look like they were blanketed with snow when the magnificent American chestnut trees cloaked themselves with white blossoms. The flowers in turn produced the tasty fruits that are so associated with the Christmas season that it’s hard to think of chestnuts without wanting to roast them over an open fire.

But that was long ago, before a botanical plague moved across the eastern United States, wiping out chestnut trees more efficiently than the fiercest wild fire.

Where great forests once stood, today there are just stumps with scraggly chestnut bushes growing out of them, and the mighty tree has been laid low.

But now, working on several fronts, scientists hope to bring the American chestnut back, restoring it to the glory that it once commanded across so many hillsides from Maine to Florida. In time, says Sandra L. Anagnostakis of the Connecticut Agricultural Experiment Station, chestnut trees should once again tower above the forest canopy. That should be possible, she adds, because of advancements in the field of genetics, and a bit of good luck.

Stubborn Fungus

It is hard to imagine just how grand those old forests were. According to the American Chestnut Foundation, which is leading the charge to restore the chestnut, mature trees were indeed awesome, towering as much as 100 feet above the ground, with trunks measuring as much as 10 feet in diameter.

No wonder they became known as the redwoods of the East.

But the end of the chestnut came quickly. In 1904, a bark disease was detected in trees in the New York City area. It turned out that the disease was caused by a fungus, Cryphonectria parasitica, that arrived in this country with a chestnut tree imported from Asia.

The manner in which the fungus spread was particularly insidious. Wildlife ranging from bears to squirrels ate the nuts, but as they scurried about the forest they spread the fungus, which even infected the soil. The fungus is as healthy today as it was decades ago.

Even a light rainfall expanded the range of the fungus. Raindrops hitting the ground caused spores to bounce up and be carried away by the wind or birds, to do their damage elsewhere. By the 1930s, virtually the entire chestnut forest had been wiped out.

Early efforts to control the fungus with toxic chemicals failed. Even clearcutting and burning did little to stop the spread of the disease, which killed everything but the roots. New spouts that came up from the root system were quickly wounded and died.

Scientists scrambled for ways to preserve this giant of the forest, but with little success. Then a few years ago scientists in France made a critical discovery. A related fungus caused damage to chestnut trees, but it did not kill them.

Wounded Survivors

Anagnostakis began treating the wounds in American chestnut trees with the non-lethal fungus, hoping to inoculate them against the fatal disease. She found that while it didn’t cure the disease, it held it in check. Her “bio control” method could keep young American chestnut trees alive long enough for them to reach maturity and flower and reproduce.

The surviving trees weren’t a thing of beauty, because the fungus caused deep wounds that left the trees gnarled and of no value as timber.

But at least it was a start.

In the meantime, scientists had discovered that Asian chestnut trees were somehow able to resist the fungus. Asian chestnuts, like their European cousins, are smaller trees and they can’t compete in American forests with taller trees, particularly oaks. Unless the chestnut towers over the forest canopy, it doesn’t get enough sun to flower and reproduce.

But Anagnostakis and others, saw an opening. Researchers found that at least two genes in the Asian chestnut allowed it to resist the fungus. The hope of survival for the American chestnut rested in transferring those genes.

So researchers began an aggressive cross breeding program, combining the Asian chestnut with its bigger American cousin in a surprisingly low-tech procedure.

Paper Bag Breeding

Working with experimental trees on the research station’s Connecticut farm, Anagnostakis waited for the flowers on the trees to begin to bloom, then she covered them with a paper bag to isolate them from pollen. After the flowers became fertile, the bag was removed, and the desired pollen was simply dumped on the flowers. Then the bag was replaced.

“We wait until fall and go around and cut all those paper bags off and take the nuts out and store them away for the winter,” she says. “In the spring, when the nuts have germinated, we plant them and we have another generation ready to go.”

By continually cross breeding, she has produced trees that are 15/16th American chestnut trees, and only 1/16th Asian. She plans to continue that process until the only Asian component is the desired genes that protect the tree from the fungus.

So the researchers are using biological warfare to protect the new trees from the fungus and genetic engineering to produce American chestnut trees that are genetically equipped to fight their mortal enemy.

In time, she says, she expects to see the chestnut restored to its past glory.

A Tree With History

Prized for its timber as well as its nutritious nuts, the trees were critical, especially to the people of Appalachia in the heart of the chestnut forest. The nuts were an important cash crop for many impoverished families who would cram their attics full of burlap bags packed with chestnuts. When the holidays approached, the bags were loaded onto railroad cars bound for the cities of New England.

The trunk of the chestnut tree was so straight that loggers could fill an entire railroad car with boards from a single tree. The straight grained wood was lighter than oak, and more rot resistant than redwood, lending itself to everything from telephone poles to fine furniture.

It didn’t take long for the fungus to wipe out the trees. Today, the survivors look more like bushes growing out of the stumps of fallen ancestors.

But there’s a bit of holiday cheer in the forest. Perhaps, just perhaps, the chestnut may finally be on the road to recovery.

Then we can really sing that old tune again, and roast a few chestnuts over an open fire.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.