The death and rebirth of a perfect tree
The American chestnut ruled over Appalachia before blight killed almost every tree, said journalist Kate Morgan in Sierra magazine. Through cross-breeding and gene-splicing, scientists are trying to bring it back.
IN CENTRAL PENNSYLVANIA, there are monuments to the dead. Inside centuryold barns and farmhouses, ceiling beams and wide floor planks that are straightgrained and honey red with age serve as reminders of one of the deadliest epidemics to ever reach American shores. Between 1904 and 1940, some 3.5 billion American chestnut trees, the giants of the Appalachian hardwood forest, succumbed to a fungal blight called Cryphonectria parasitica.
The loss was stunning—not just for sprawling ecosystems across much of the eastern United States, where the tree was a keystone species, but also for the Appalachian way of life. When the profitable nuts and timber disappeared, the Appalachian landscape was reshaped twice over: first by the death of the chestnuts, then by a century of coal mining that stripped and scarred the earth, leaving piles of rubble in its wake.
By almost any metric, the American chestnut was a perfect tree. Massive, fastgrowing, and rot-resistant, it was easy to mill into cabin logs, furniture, fence posts, and railroad ties. After being harvested, it resprouted; in 20 years, it was ready for the sawyer again. Wide limbs spanned the canopy, filtering sunlight and creating a diverse, layered forest below. Cooper’s hawks nested in the high branches, wild turkeys in the lower forks. Cherokee people made dough from the crushed nuts, treated heart troubles with the leaves, and dressed wounds with astringent brewed from the sprouts. And in the fall, when the chestnuts piled up in carpets half a foot thick, white settler families collected and sold them by the bushel.
In a range stretching from southern Maine to the Florida Panhandle and west to the Mississippi River, the chestnut dominated the landscape, accounting for a quarter of all trees in the eastern hardwood forest. In Appalachia, the heart of the tree’s range, generations of people were rocked in chestnut cradles and buried in chestnut caskets.
But the dominance wouldn’t last. In 1904, a forester noticed something odd happening to the chestnuts at the Bronx Zoo in New York. The trees were developing cankers surrounded by strange spotty, orangeyellow patches. He called in mycologist William A. Murrill to examine the fungus. By the time Murrill published his findings just over a year later, the disease had spread to New Jersey, Maryland, the District of Columbia, and Virginia.
Murrill warned his incredulous colleagues that the blight—imported on ornamental Japanese chestnuts as early as 1876—would kill every chestnut tree. By 1904 it was already too late to stop it.
SARA FERN FITZSIMMONS is part of a small army of biologists, ecologists, foresters, and activists who are passionately dedicated to bringing back the iconic tree. Shouting over the hum of a greenhouse fan, Fitzsimmons, the director of restoration at The American Chestnut Foundation (TACF), is waving a golden, jagged-edged leaf at me as she explains that the chestnut genus, Castanea, originated in China. The Cryphonectria parasitica blight fungus survives on dead tree tissue, and in the three species of chestnuts in China, it lives mostly unobtrusively, feeding on damaged cambium under the bark where a tree’s been wounded by weather, an animal, or insects. These trees, which evolved alongside the blight, grow burl-like callus
“People think the Chinese chestnuts are immune to the blight; there’s no such thing as immunity,” Fitzsimmons says. “But they can wall off the infection really quickly, surround it with that callus tissue, and stop it progressing.” Japanese chestnuts have a resistance similar to the Chinese varieties, she says, while the American variety has very little. Once Cryphonectria parasitica colonizes a wound on an American chestnut, it’s unstoppable. It polishes off the already-dead tissue, then secretes oxalic acid, a toxin that kills the chestnut’s cells, feeding the fungus and killing the tree.
Carried on the wind, the blight spread an estimated 50 miles a year, tree by tree. First a canker would appear, causing the bark to bulge or sink. Soon the wound would burst open, sending spores sailing outward from an ocher-colored blotch. The mighty upper limbs died first, then the trunk. By 1910, coalitions had been formed and quarantine lines drawn. Boy Scouts were enlisted to scour forests and cut down blighted trees. It was no use. By the time the blight had run its course, nearly 4 billion American chestnuts across 300,000 square miles were gone.
Meanwhile, the coal industry has left its own wake of destruction in the Appalachian forest. In a single scoop, an average-size Bucyrus-Erie dragline can move more than 100 tons of earth. This machine drove the biggest technological shift mining has ever seen. The dragline lifts away the topsoil and rock and deposits it in nearby valleys, reshaping entire topographies and leaving behind wide swaths of barren, contaminated land. While trees didn’t root in the compacted earth, fast-growing, nonnative grasses did, creating meadows where there ought to be forests.
Itissue around the wounds, creating barriers that keep the fungus from spreading.
’M PICKING MY way through bramble, trying to keep up with Fitzsimmons. The hillside we’re standing on is former mineland in Coal Township, an hour north
plicated, he posited, a simpler solution would be to add a defense mechanism from elsewhere. Wheat and other cereals produce an enzyme, known as OxO, that protects them “from disease caused by oxalic acid by producing oxalate oxidase,” Powell says. The chestnut blight “all rotates around this acid. If you can get rid of that, all of a sudden it can’t get into healthy tissue.”
Powell started with embryos from an American chestnut near Binghamton, N.Y., that hadn’t totally succumbed to the blight. He inserted a gene that produces the OxO enzyme and grew seedlings that looked like tiny palm trees on petri dish islands of agar. The first petri dish chestnuts were grown in them with the advanced backcross trees.
“At this point, the transgenics are under tight guidelines,” she says. “The USDA permitting guidelines leave no chance, zero risk, of that gene entering the wild and getting out of your control. It’s impossible, following these guidelines, for it to escape.” But release into the wild, Powell and Fitzsimmons agree, is the next step on the road to restoration. In early 2020, Powell and his team submitted a nearly 300-page petition to the USDA, requesting that the agency deregulate Darling 58, making it legal for anyone to plant it anywhere. The move would be the first time a genetically modified organism was approved for release into the wild.
If Darling 58 is approved for release and its seeds are planted—by members of the public, restoration groups, and anyone else who wants them—their locations will be entered into a TACF database. Then, if all goes according to plan, they’ll reproduce, pollinating both wild shoots and backcrossed trees. The result will be genetic diversity and resistance: Of Darling 58’s offspring, “half give you the resistance, and half preserve the wild type,” Powell says. “In 100 years, a transgenic tree will still be producing wild ones.”
That is, as Fitzsimmons sees it, the only way to give the American chestnut a fighting chance. “People think Darling 58 is a silver bullet, or that the OxO gene is immunity, but it is not.” The path to resistance, she says, requires both the variable Chinesederived resistance of the backcrosses and the OxO gene expression of the transgenics. Turn the coalfields into thriving, mature chestnut forests and the trees could do the rest, seeding themselves into adjacent forestlands. Slowly, from these debased landscapes, a new forest would expand outward. Imagine autumn in a sloping grove, broad, craggy trunks climbing the hillside. Black bears, fat on sweet chestnuts, drag their feet on the loamy ground, and salamanders skitter through pools in the forest that was and the forest that could be.
“We call this a century project,” Powell says. “To get it to look even somewhat like it did before the blight is going to take centuries. It’s for the next generation—it’s planting a tree you’ll never enjoy the shade of.” It requires a kind of optimism unique to those who look at the badland of a strip mine and envision a forest, the kind of faith held by those who plant a seed in desecrated ground and say a prayer.