Saving the American Chestnut Tree

An invasive fungus has killed billions of American chestnut trees since the early 1900s. Forestry experts in southeastern Ohio may have found a solution.

His branches ruffle in the light breeze under a brilliant sun, a lone sentry in a clearing surrounded by the traditional guardians of Ohio’s forests. The hemlocks, maples, white ash, and sycamores seem to watch over him, giving the youngster the space and energy to grow. And he has.

Illustration by Andrew Davison

At age 3, he’s already more than 12 feet tall, and his distinctive foliage suggests he is healthy and ready to reign as the King of Hocking Hills. Instead, he’ll likely wither and die within the next 10 years.

As pioneers poured over the Allegheny Mountains in the 1780s and began settling eastern Ohio, they passed under the canopy of millions of American chestnut trees. We would be awestruck by what they saw: mammoth brownish-gray columns of bark towering 100 feet in the air, the first branches not poking out until halfway up to heaven before splaying their splendor in a crown of green sawtooth leaves.

Below, the barren forest floor awaited the first crisp days of autumn, when the trees’ fertilized yellow-brown burrs would burst open and release a shower of shiny, mahogany-colored nuts. They were manna from heaven, an annual gift that fed people and animals. They were nutritious and delicious. There were so many, legend had it that the early settlers could walk for miles on a carpet of chestnuts.

The wood itself sported a coarse grain and a range of colors. And there was a lot of it. The trunks, at their base, could exceed eight feet in diameter. Chestnut wood was almost as strong as oak but with half the weight. It was easy to work with. Pioneers used it to build their cabins and barns, and, because it was rot-resistant, it was a “must have” for foundations and floors. Leftover wood was made into bed frames, cabinets, tables, and chairs.

“It was known as the perfect tree,” says Carolyn Keiffer, a botany professor at Miami University’s Middletown campus and president of the Ohio chapter of The American Chestnut Foundation (TACF). “Everyone loved the chestnut. The pioneers needed the chestnut. Even today, it makes everyone smile.”

Nearly 4 billion chestnut trees stood guard down the spine of the Appalachian Mountains from Maine to Georgia. They were about a quarter of the trees in the forest, and their range extended west into Ohio, about as far as Chillicothe. Then, around the turn of the 20th century, a blight arrived with imported Asian chestnut trees and infected the native trees.

“It’s a good early example about how transportation is killing the world,” says Brian McCarthy, a professor of ecology at Ohio University. “We’re seeing it now with the emerald ash borer and the Asian longhorn beetle. Imported insects, invasive plants, and pathogens are carried here, and the native ecosystem has no way to defend itself.”

Under a spreading chestnut-tree
The village smithy stands;
The smith, a mighty man is he,
With large and sinewy hands;
And the muscles of his brawny arms
Are strong as iron bands.
—Henry Wadsworth Longfellow (1840)


The Asian chestnut trees were exotic, and American consumers loved them. They had no idea they were planting a Trojan horse. Embedded in its genome was a lethal fungus, cryphonectria parasitica, neutralized in Asia through adaptation over centuries. But it was an unrelenting killer here. The first American chestnut died in what is now the Bronx Zoo in 1904, and the fungus marched like an unstoppable army, reaching Ohio in 1932. Within three years, it had all but wiped out our chestnut trees. The species is now known by scientists as “functionally extinct.”

Stephen Rist

Photograph by Carlie Burton

“It’s an airborne fungus that can be spread through the wind and by birds or squirrels,” Stephen Rist explains as we examine a stand of chestnuts planted by the Ohio Department of Natural Resources (ODNR). A few yards away, the roar of a couple of motorcycles brutalizes the silence, then suddenly passes, returning Hocking Hills State Forest to sweet birdsong.

Rist, who manages ODNR District 4, uses his long legs to jump fallen logs and stomp down thick underbrush, assorted seedlings, and weeds in his path. These chestnuts are hybrids: 15/16th American and 1/16th blight-resistant Asian. It’s a crossbreeding experiment, one of three strategies TACF is employing in what’s already a decades-long effort to restore the tree. The foundation calls it the 3BUR strategy, which stands for breeding, biotechnology, and biocontrol united for restoration. It sounds a bit like a marketing campaign, but it’s pure science—though some of it is controversial.

The saplings are encased in nearly opaque 5-foot-tall white tubes, but their branches are starting to poke out the top. They aren’t sick yet, but they’re sharing their environment with their killer. “The fungus is everywhere. It’s probably on the soles of your shoes right now,” says Rist ominously, strangely making me scratch my ankles.

Chestnut saplings in Hocking Hills State Park.

Photograph by Carlie Burton

Just a few hundred yards from this hillside lies the spot where Keiffer fell in love with the chestnut. With interests in both botany and hunting, she was drawn to a study known as “restorative ecology.” An undergrad course at Ohio University took her to Hocking Hills, where she discovered a chestnut sprout near Old Man’s Cave. “I tucked that in the back of my head and then, in grad school at OU, I chose the chestnut for a seminar I had to do on a disease or pathogen,” she says.

Keiffer asked for information from TACF and was dumbfounded with the material they sent her. “I couldn’t believe there were people out there who’d take the time to help a student,” she remembers. Her love connection with the chestnut was complete.

“She walked into my office one day and asked me what I knew about the chestnut tree, and I said, Well, not very much,” McCarthy recalls of his grad student. “It wasn’t long after that she introduced me to TACF, and I started to look at how we might insert a restoration colony into our forest ecosystem.” He’s now the chairman of TACF’s board of directors.

McCarthy was particularly fascinated with a stand of chestnuts near La Crosse, Wisconsin, that was still standing tall and healthy. In the 1880s, a farmer had brought about a dozen chestnuts from central Pennsylvania, planted the seeds 50 feet apart, and let nature take its course. They flourished and procreated up to 6,000 healthy trees, probably because Wisconsin was more than 500 miles west of the chestnut’s natural range.

It took 102 years, but the fungus finally caught up with this defiant stand of trees. Wisconsin forestry experts moved aggressively—even coating the trees in bleach—but the fungus was stubbornly resilient. Finally, in 1992, scientists from Michigan State University and the University of West Virginia tried a biocontrol, inserting into the infected trees a virus extracted from a tree canker in Florence, Italy. Its chemistry weakened the chestnut fungus, giving the host tree the boost it needed to stay alive.

The approach worked for a while, McCarthy notes, but the combination of harsh Wisconsin winters and a severe drought around 2010 seems to have weakened the Tuscan virus and, sadly, not the fungus. The Wisconsin chestnut miracle grove is failing, but McCarthy believes it’s proved that biocontrol is a viable strategy.

O chestnut tree, great rooted blossomer,
Are you the leaf, the blossom or the bole?
O body swayed to music, O brightening glance,
How can we know the dancer from the dance?
—William Butler Yeats (1926)


What’s intriguing about the chestnut is that it’s as stubborn as its mortal enemy. The fungus kills the tree, but it doesn’t kill the roots. So, when a chestnut tree succumbs and eventually falls, stump shoots or root shoots spring forth to begin the life-and-death cycle all over again.

An infected American chestnut tree

Photograph by Carlie Burton

An infected American chestnut tree

Photograph by Carlie Burton

The sprouts grow quickly, and their smooth bark, like a baby’s skin, shows no break. But, Keiffer says, after a tree reaches five to seven years old and begins to bear fruit, the expanding bark roughens and small breaks, some imperceptible to the human eye, appear. Insects may enter and make the holes bigger. Squirrels may scramble up the bark looking for the nuts, their claws ripping at the bark.

The fungal spores, like running backs who see a hole in the defensive line, break through. The tree is ultimately doomed.

Rist examines and photographs an infected tree in the Zaleski State Forest just west of Athens. The trunk is disfigured with dozens of bright orange pustules, the fungus’s fatal signature. They contain oxalic acid that will slip under the bark and attack the cambium, the next layer in, destroying the tree’s growth hormones first. Eventually, they’ll form a ring around the tree, choking it to death. Everything above the ring will die; everything below, including those reincarnated roots, will live.

The crossbreeding strategy is designed to add just enough genetic material from the Asian chestnut to give the overall tree a viable defense. Asian chestnuts are attacked by the fungus too, but the species has built up enough immunity that it isn’t fatal. Scientists have crossed the American chestnut with the Asian variety through several generations now to the point where the overall tree is about 95 percent American. The crossbreeding has shown some promise, but it’s a slow process. Trees have their own timetable.

“What’s missing [with the crossbreeding] is the magnificent stature,” says Tom Brochu, a retired company executive from Veritiv Corporation, a spinoff of International Paper. Brochu now serves as a trail ambassador at the Cincinnati Nature Center, where two years ago he planted about a dozen pure-bred American chestnuts. “It’s for experiential learning,” he says. “It’s for the kids who come here. They learn about this great tree and what’s happened to it. Maybe it inspires them to take an interest in field biology.”

Brochu anticipates no miracles for his trees. Chestnuts don’t like southwestern Ohio’s limestone-based alkaline soil, but it won’t kill them. The fungus will.

The American-Asian crossbred trees, even after several generations, produce shorter, bushier offspring, mimicking the characteristics of the Asian chestnut. They do produce nuts like other chestnut varieties, but they’re not as sweet or nutritious and their output per tree falls short of the prolific American chestnut.

Perhaps as discouraging, Keiffer and McCarthy point out, is the discovery through gene-mapping technology that resistance to the blight is imprinted on nine different chromosomes of the Asian chestnut, not two as originally thought. “That’s set the whole traditional crossbreeding program back,” Keiffer says. McCarthy agrees, noting, “This might explain why the results we’ve gotten aren’t what they should be after 30 years of crossbreeding.”

Continuous crossbreeding by recrossing the best with the best might still work in the end, but those Asian bushy chromosomes won’t go quietly.

A young chestnut tree in Hocking Hills State Park. Will it live beyond its teen years?

Photograph by Carlie Burton

Another approach to breeding in fungus resistance is gene editing, in which the American chestnut genome is changed to reduce its vulnerability to the fungus, replacing the defective genes with those from another species. For more than 30 years, scientists at the State University of New York College of Environmental Science and Forestry (SUNY-ESF) have been working to create a genetically-engineered, blight-resistant American chestnut using enzymes specifically targeted to insert a gene from the ordinary wheat plant into the chestnut’s DNA sequence. It’s known as CRISPR technology.

Scientists knew the wheat gene contained codes for an enzyme called oxalate oxidase, which through a chemical reaction breaks down the oxalic acid the fungus releases into the chestnut. It didn’t work at first, but when SUNY scientists amped up the gene sequence, the inoculated trees were blight resistant and passed their resistance to the next generation. The trees produced nuts, and tests demonstrated they mimicked their natural “cousins.” They’re now known as Darling 58 trees—named for a man in western New York on whose property a single healthy, nut-producing American chestnut was discovered in 1989.

For the last six years, the growing trees have been sequestered behind a high deer fence in a special field near the SUNY campus in Syracuse, closely monitored and government regulated. Their reproductive parts are double bagged, so their pollen doesn’t leave quarantine. The plan is, when approved by three agencies of the federal government, to introduce them to the forest, breeding them with different strands of existing American chestnuts to achieve a new variety of the species.

The process is controversial, as all genetically modified plants seem to be. It’s caused a rift within TACF, and some long-time members have left the organization. It concerns some proponents of crossbreeding who worry this shiny new object will distract and overwhelm their continuing research. And it’s alarmed some in the environmental community, who question the ethics and the unknown impact on the existing forest.

“We’re not doing anything weird here,” McCarthy insists, noting this specific wheat gene is in bread, cereal, peanuts, bananas, spinach, and more than 100 other foods. “The idea is to take a gene from a closely related source and move it to where nature can take its course.”

Keiffer agrees, adding, “We’re not creating a Frankenfood here. This is real science. It’s a tool we need to consider.”

Brochu, who has an undergraduate degree from SUNY-ESF, is excited about the work his alma mater is doing and has filed comments with the U.S. Department of Agriculture, the first federal agency to review SUNY’s petition to release Darling 58 into the forest ecology. The Food and Drug Administration and the Environmental Protection Agency will need to approve the genetically modified tree as well, so the process could take as long as five years.

“This is good science even in this confrontational era,” Brochu asserts, admitting he can become emotional about the American chestnut. “As a human race, we have done a lot of damage to our environment. Wouldn’t it be amazing if, in our lifetimes, we saved a species?”

Chestnuts roasting on an open fire
Jack Frost nipping at your nose
Yuletide carols being sung by a choir
And folks dressed up like Eskimos.
—Robert Wells and Mel Torme (1945)


Back in the Hocking Hills woods, Rist and I relax outside an ODNR cabin. He tells me about his two young sons and how they love the outdoors. A flock of noisy Canada geese interrupt his train of thought, but I get it: His sons are just like him. A fat, green walnut falls from above, bouncing off the top of my head. Rist laughs, noting the forest has a sense of humor.

He also knows it’s missing something—a skyline highlighted by the stately American chestnut. He imagines a future forest rejuvenated by grafts from today’s chestnuts and bred with either crossbred or genetically-modified trees, the dreaded fungus rendered benign.

Rist makes it clear he’d love to be one of the new Johnny Appleseeds who will dig the holes and drop the seeds into southeastern Ohio’s acidic soil. And he hopes his two young sons will one day, like the original pioneers, walk on a carpet of chestnuts.

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