The American Chestnut
NOT SO LONG AGO, the American chestnut (Castanea dentata) by many accounts was the most prized and plentiful tree in our eastern forests. It was said that a squirrel could make its way from Maine to Georgia by jumping from one chestnut tree to another without ever having to touch the ground. Fast growing, especially for a deciduous tree, it could reach an impressive height (75 to 100 feet) and width (up to nine feet), and could live for several hundred years. It produced an abundant supply of edible nuts that were a staple for wildlife in the fall, especially whitetail deer, wild turkeys and black bear (and were a favorite seasonal human food, too).
Chestnuts were economically valuable trees, as well. The wood was highly valued for its strength, light weight and rot resistance; its uses ranged from framing houses and barns to crafting furniture, fence posts and even telephone poles. While in leaf, the chestnut provided welcome shade on a clear summer day. From a human standpoint, it was as close to an ideal tree as you could get.
Surviving and competing with other native North American trees for 40 million years, by 1900 an estimated three to four billion chestnut trees covered an area of 200 million acres.
Yet within 50 years, almost every American chestnut tree was dead.
The trees were driven to near-extinction by a lethal fungal pathogen that became known as the chestnut blight, introduced into New York in 1905 on exotic Chinese chestnut seedlings imported from Japan. The seedlings that carried the disease had evolved and adapted to coexist with it, but the native American chestnut had never been exposed to the disease and had no resistance to it at all. Many foresters and others believe what resulted was the greatest ecological disaster to occur on wooded land in all human history.
Given the enormity of the loss, both environmentally and economically, it’s not surprising that much effort has been focused on bringing the chestnut back from the brink of extinction. The goal has been to develop a blight-resistant strain of the tree and, over time, reintroduce it to its natural range.
At the forefront of this effort is The American Chestnut Foundation, which has chapters in 16 eastern states and a major research farm in Meadowview, Virginia. Plant scientists at the Foundation use a method known as backcross breeding to introduce blight resistance into the native tree. This starts by crossing the American chestnut with its Chinese counterpart, then cross breeding the progeny for successive generations with native chestnuts to restore as many of the characteristics of the native strain as possible. The research farm currently has some 18,000 hybrid chestnut trees at various stages of growth.
Researchers elsewhere have taken different approaches. Inter-crossing involves working with American chestnuts only—specifically living trees that appear to have some degree of blight resistance. A third approach that is showing promise involves genetic engineering—introducing genetic material from an entirely different species of plant, specifically wheat, to develop a blight-resistant tree. The effort to develop this transgenic American chestnut is being led by SUNY College of Environmental Science and Forestry in Syracuse.
I’m tempted to buy another five trees and plant them next spring, notwithstanding the likelihood that it would be the local wildlife and a subsequent generation of humans who would reap the benefits.
Fortunately, plant scientists still have native material to work with from a few different sources. First, a small number of isolated chestnuts in eastern forests have not, as yet, been affected by the blight. Second, some chestnuts living outside the tree’s normal range also exist. In northern Michigan, for example, there is a grove of chestnuts, presumably planted by nineteenth-century settlers, that the blight has not reached. A modest number of chestnuts also have been relocated to Oregon and California. Third, small, shrub-size American chestnuts can still be found within the tree’s traditional range. Even after the above-ground portion of a mature chestnut has been killed by the blight and rotted away, new shoots can sprout from the still-living root system. These “stump sprouts” are doomed to succumb to the disease by the time they reach a height of 15 or 20 feet; until then, however, they can provide viable genetic material for researchers.
Twenty years ago, in this magazine, I read an article about the fate of the American chestnut and efforts to restore it. [Leslie Coons, “An American Classic Resurrected,” The Valley Table number 2, November 1998.] I was intrigued and inspired. I located a tree nursery in Kentucky that was selling young, grafted trees with enough of the Asian species in them to withstand the blight. The following spring I ordered and planted five trees. Over the next several years, three of them died (possibly due to mismanagement on my part or continuous browsing by deer), but two survived and are still with us. They are now over 30 feet high.
A decade ago, our two surviving chestnuts fruited for the first time, giving a couple of handfuls of tasty nuts. With each ensuing year they have been more generous. This fall they were positively bountiful: I estimate a harvest of about 3,000 nuts.
While still on the trees, the nuts are enclosed in a substantial outer casing known as a burr. The burrs have extremely sharp spines that deter tree-climbing animals or birds looking for a high-protein meal. (They deter us, too—no sane person would attempt to pick a chestnut from the tree without sturdy leather gloves.)
In late September, the nuts begin falling to the ground. We lay large tarps on the grass under the trees, which makes it easier to gather them each morning. Conveniently, the burrs open and release their nuts just before or soon after falling from the tree (each burr often contains two or three good-sized nuts). If we leave the nuts on the ground for more than a day or two, many are nibbled by squirrels, chipmunks and other assorted rodents or disappear into the mouths of passing deer.
This fall, because of the bountiful harvest, we offered nuts for sale at our Manhattan farmers’ market. They moved well. We also kept a few for ourselves. My wife roasted them in the oven at 350˚F for 30 minutes—they were very good. (If you try this, be sure to make a small cut in the skin of each nut before roasting to prevent them from bursting.)
It seems the ongoing research to produce a more bona fide American chestnut is paying off: The hybrid trees available today (compared with 20 years ago) have more of the native species in them and less of the Asian. I’m tempted to buy another five trees and plant them next spring, notwithstanding the likelihood that it would be the local wildlife and a subsequent generation of humans who would reap the benefits.
I like to think the land, also, might appreciate the return of an old friend.
The American Chestnut Foundation (acf.org) welcomes new members and public support for its ongoing research. Basic membership is $40 per year. Membership at higher levels brings a gift of a small number of chestnut seeds from the most promising hybrids. Trees grown from these seeds will exhibit the major traits of Castanea dentata; genetically, they will be 94 percent American chestnut and 6 percent Chinese. The Foundation believes the trees will have good resistance to the blight but makes no guarantee.