Restoring the chestnut: Dalgleish considers 'love' and biology
{{youtube:medium|_29IOklUOUI, Dalgleish's students explore a question related to Chestnut tree restoration.}}
Harmony Dalgleish had been at William & Mary for only a short time before she was on a first-name basis with every chestnut tree in Williamsburg.
She name-drops a few: the three European chestnuts on Cary Street (“They have delicious nuts!”), a Chinese chestnut on Matoaka Court and a small stand of Americans chestnut out in the College Woods. These chestnuts are all different species of trees. Dalgleish, an assistant professor of biology at William & Mary, focuses her study on the native American chestnut.
Dalgleish has a number of terms for describing the American chestnut—“iconic” is one. Sadly, “functionally extinct,” is another, but, as there are native chestnuts still growing throughout the east, the species is a long way from being completely extinct.
In fact, if you want to see an American chestnut on William & Mary’s campus, just wander around the green space in front of Phi Beta Kappa Memorial Hall. South of the flagpoles, you’ll find a couple young American chestnuts. These are memorial trees, identified by markers, and planted by hand. Dalgleish said while there are many such trees gracing landscapes all across the country, mature American chestnut trees are rare in the wild, despite being one of the most common trees in Appalachian forests a century ago.
Dalgleish says that anecdotal reports tell of a time when one in four trees in Appalachian forests was an American chestnut. Then, she said, came the blight—a fungus brought to America on Asian ornamental plants proved particularly deadly to American chestnuts. Cryphonectria parasitica spread through the forests of the east, wiping out billions of mature trees, leaving just enough surviving chestnuts for hope and science.
“American chestnuts are what you could call charismatic megaflora,” she said, a play on “charismatic megafauna,” the term scientists and environmentalists use to describe animals that people go out of their way to see.
“They’re the closest thing we botanists have to polar bears and wolves,” she said. “People love this tree; they come up to me at meetings and show me their chestnut tattoos.”
Dalgleish yields to no one in her admiration for Castanea dentate, but she’s a scientist. Rather than getting inked, she studies surviving patches of American chestnuts, mainly in Maine. She collects nuts and the burrs that surround the nuts, examines historic insect collections for chestnut-related bugs, and chases down rumors and sightings of specimens. Her chestnut research is supported by the U.S. Department of Agriculture’s National Institute of Food and Agriculture. She believes that science can help Americans re-chestnut their forests—but isn’t sure if bringing back the native chestnut is a good idea.
A surprising number of people are passionate about restoring this charismatic megaflora, the botanical equivalent of the bald eagle. The tree has enjoyed persistent popular support since the days of the blight. For instance, the American Chestnut Foundation offers a free download of Dolly Parton’s ode to the tree on its web site. The Dolly download can be found alongside news on the group’s restoration and breeding efforts as well as identification and reporting information for people who believe they’ve found a native chestnut that has somehow survived the blight. Much of the interest in the native trees, Dalgleish explains, is rooted in a longing for a way of life that has all but disappeared—like the American chestnut itself.
“For one thing, they were a staple of the rural economy,” she said. “But I also think it was a striking moment in the psyche, to see these trees die so quickly and to see so many of them go. I hear people who remember that or have heard their grandparents talking about it.”
She points out that beyond the considerable Americana interest, there also is a lot for a woodlands biologist to like about the American chestnut, especially in comparison to the oaks that have largely replaced them in Eastern forests. Dalgleish lists the virtues of the species: They grow more quickly than oaks, for starters, and can reproduce at an earlier age. The trees can grow to an enormous size—American chestnuts taller than 100 feet were not uncommon. Chestnuts not only produce a lot of rot- and insect-resistant lumber, but they also are potentially more efficient at sequestering carbon than oaks. The nuts, delicious when you roast them on an open fire with Jack Frost nipping at your nose, form the base of a woodlands food web that evidence suggests would support fewer outbreaks of Lyme disease and other vector-borne human maladies.
Dalgleish explained that a chestnut tree produces a nut crop reliably every year, whereas oaks operate on a boom-and-bust proposition, the acorns raining down during high-yield “mast years.” In off years, oaks produce few if any acorns. Mast years throw the food web into overdrive, resulting in a jump in the population of mammals, hosts for potentially disease-carrying ticks.
Her research has included running up simulations that predict that the steady nut production of American chestnuts would result in fewer spikes in mammal population, spikes that current research has shown correspond with increases in tick population—and the diseases they carry.
The American Chestnut Foundation has thousands of members and is dedicated to finding and preserving surviving trees as well as restoring the American chestnut to the woods of the U.S. The group’s enemy, of course, is the blight.
Once it takes hold, chestnut blight is easy to spot, Dalgleish explained, because of the distinctive orange cankers that the fungus forms on the bark. The blight girdles the tree, cutting off the capillary action of phloem and xylem, the tissues that facilitate the transfer of nutrients and water. Eventually the tree dies from the ground up.
The blight was first noticed in New York in 1904, after it was brought in on ornamental plants from Asia. Dalgleish said the blight’s rapid proliferation was helped by the denseness of the growth of its victims in eastern forests.
“The blight’s movement has been estimated to be about 20 to 50 miles per year, because American chestnut was so common in the forest and because it was so highly susceptible to blight,” she said. “Basically, when a tree got it, it died.”
Although the blight had wiped out most of the American chestnuts by World War II, Dalgleish points out that the tree retains its mystique decades later, even though there are fewer people each day who remember the great pre-blight stands of American chestnut.
She says that there are a number of possibilities for the re-chestnutting of our forests. For one thing, there are a lot of American chestnuts in them thar hills—they’re just mostly underground.
“Chestnut is actually a pretty prolific resprouter,” she explains. “Even though the fungus attacks the above-ground stem, it doesn’t penetrate to the root system, so the root system stays healthy. So the whole tree doesn’t die, just the large above-ground stem, which is the main reason chestnuts aren’t extinct today. You can go out into the woods and see chestnut sprouts. Most of those stems are as big around as my pinky.”
The millions of resprouting—but never maturing—chestnuts in America are the main reason that botanists use the term “functionally extinct.” The resprouting root systems could grow into mature trees in a decade and, if there was a gap in the surrounding tree canopy, a resprouted chestnut could grow to be a new forest giant. It’s a realistic scenario—if the blight could be controlled.
“That’s a big ‘if,’ probably an insurmountable ‘if,’” she said. She added that the chestnut blight didn’t die out with the American chestnuts. Rather, the fungus survives in the woods, mainly on trees that can survive the effects of its cankers more successfully.
“Because we can’t get rid of the fungus, there have been these different approaches to producing blight-resistant chestnut trees: This does not mean ‘blight immune,’” she said. “The tree is able to deal with the infection and produce a healing canker, rather than a canker that kills the tree.”
Early ideas to replace the lost American chestnuts by seeding the woods with Chinese and European chestnuts were pretty much nonstarters, she said. These trees have built-in blight resistance, but don’t grow tall enough to compete with the oaks in our forests. Dalgleish added that the European and Chinese chestnuts do make excellent orchard trees and are the source of virtually all the food chestnuts being sold.
The American Chestnut Foundation (TACF) is using genetics to confound the blight. Dalgleish said that since 1983, TACF is tapping into the blight resistance of the Chinese chestnut through an old orchardist’s technique known as backcrossing.
“You breed a pure American chestnut with a Chinese chestnut, and you get what you call your F1 generation. It’s half American, half Chinese,” she said. “And then you breed your F1 to a pure American: That’s your backcross.”
Chestnut breeders backcross three more times, breeding each generation to a pure American chestnut, resulting in a tree that has 94 percent American genes.
“It looks like an American chestnut,” she said. “But it has the Chinese genes necessary for blight resistance.”
TACF distributes its backcrossed chestnuts to its members for planting. Another group, the American Chestnut Cooperators Foundation, is also working on breeding blight-resistant American chestnuts. Dalgleish says this group breeds from native chestnut “mother trees” that have demonstrated blight resistance, striving to breed blight resistance in 100 percent native trees.
Dalgleish is not a member of TACF, the ACCF or any of the other advocacy groups. She maintains a symbiotic relationship, working with the groups on chestnut research. As a scientist, Dalgleish works hard to maintain scientific detachment and remains agnostic on the goal of the chestnut enthusiasts to restore the American chestnut to the woods of America.
“I struggle with that question. I kind of vacillate,” she said. “I really do. This was such an important tree and having an additional seed-producing tree in the forest, in addition to the oaks, would be a good thing for the wildlife. But what would that do to the oaks and the food web? That’s the kind of thing I grapple with in my research.”
