November 27, 2013
Originally published November 24, 2012
The American chestnut was once a keystone species in eastern forests; it was prized for its sweet nuts, rot-resistant wood, and picturesque beauty. But it was decimated by a tiny fungus accidentally imported from Japan. Now a few organizations are working to restore "The Mighty Giant."
Thad Jones is a park ranger who works, among other places, in a grove in Sewickley Heights Park. The hillside appears to be a work in progress. Small, thin saplings, most of them two feet tall at best, are poking up from white plastic cones. A smattering of maple, beech, and oak trees shade them. A sapling catches Jones' eye.
"Here’s a great one right here," he says. "My gosh. Look at the lobes on that. That is American."
The sapling’s long, cresting, canoe-shaped leaf lobes are a fundamental characteristic of the American chestnut, a tree once known as “The Redwood of the East” and “Mighty Giant.”
"This was the foundation species of the eastern deciduous forest," Jones says. "It fed everything. A keystone species of our ecology, a dominant species."
The beloved tree’s dominion stretched through all of Appalachia. The American chestnut grows fast, straight and strong—sometimes 150-feet tall and up to 15-feet wide, and its natural rot resistance makes it perfect for timber. They were popular with people—and squirrels—for their reliable, heavy yield of sweet nuts. Another nickname for the American chestnut was “The Perfect Tree.”
In 1904, an invader from Japan, Cryphonectria parasitica, was discovered in New York City’s Bronx Botanical Gardens. It’s a tree fungus, and the American chestnut has no natural resistance. As the blight spread unchecked, the nation could only watch in sadness. By the 1940s, the tiny fungus felled over four billion Mighty Giants, and for all practical purposes, eliminating the population. Although the battle between giant and spore continues today, it’s on a much smaller scale.
In another part of the park a 10-year-old tree stretches 20-feet tall; it seems like a fine specimen. But Jones looks closely at the trunk.
"That’s the fungus right there," he says. "See that bark. It peels off very easily. That’s Cryphonectria parasitica. And the fruiting bodies that release the pores you see on the surface. It kind of has two life stages. It produces a fungal mat beneath the bark, and then it blooms or erupts and releases the spores."
Within a few years, this tree almost will be a ghost. The ghost trees re-sprout from their roots; the fungus can’t survive underground, and this has long inspired hope of restoring the American chestnut to its former glory. But the shoots aren’t nearly as strong as the parent tree; deer will eat them, and other trees will grow faster and steal their light. Even if a tree can stretch tall, the blight eventually kills it.
Early USDA efforts to hybridize the tree with resistant Chinese and Japanese varieties didn’t work because the hybrids didn’t capture the characteristics of the American version. They were shorter, bushier, and less desirable. So the program was shut down in the 1960s.
Enter the American Chestnut Foundation. The organization was founded in 1983 with a singular goal: use scientific methodology to restore blight-resistant American chestnut trees to their former habitats. Sara Fitzsimmons is the Northern Appalachian Science Coordinator. She’s using a technique called backcross breading.
"So basically the idea is to take one trait of interest—in this case it’s blight resistance—and put it into the overall network of traits for a species," she says.
This is old-school botany. In each round of breeding, the tree is crossed back to maximize desired characteristics; the goal in this case is to have a tree that is 95 percent American chestnut—just like the native tree, but with just enough Asian genetics to be resistant to the blight.
"We do that through a minimum of 6 breeding generations. Each one of them then takes between 5-10 years. It’s pretty time and resource intensive," Fitzsimmons says.
Scientists at the American Chestnut Foundation are confidant their program will work, but there is no guarantee the tree can return to dominance. And even if it does, they won’t become a keystone species again for at least 100 years—nobody currently working on the project will be alive to see it.
So if we've lived without the American chestnut for over 100 years, why do we need it now?
"If you look at our forests today, you see a great loss in mass-producing species; things like oaks, we’re losing them primarily because of poor regeneration. So having something like the chestnut can build up the hard mass of our forest and hopefully make our wildlife a little healthier," Fitzsimmons says.
She says from an economic standpoint, the chestnut was highly valuable and can be, again.