American chestnut: The king is poised for a comeback

By Reeve Gutsell For the Gazette

Published in print: Saturday, February 13, 2016

To be clear, it’s not that you can’t find American chestnuts (Castanea dentata) at all. In fact, small specimens are not uncommon, usually in the form of stump sprouts, rarely more than 20 feet tall. What you will not see — except, possibly, in a few remote locations — are stands of full-grown, living, healthy American chestnuts.

The reason for this is the arrival of the chestnut blight in the early 1900s.

Chestnuts belong to the Fagaceae (beech) family, members of which are spread throughout the world. In Asia, over thousands of years, the Chinese chestnut (Castanea mollissima) co-evolved with the fungus Cryphonectria parasitica; for these trees, the fungus is mildly destructive but not deadly. American chestnuts, however, had developed no such resistance.

In 1904, Hermann Merkel, chief forester for the Bronx Zoo, first noticed a new problem on a few of his chestnuts — a ring of dry bark surrounding a patch of small orange dots. He treated the unknown infections with a fungicide, and waited and watched.

Unfortunately, by the following spring, nearly every chestnut in his forest was affected, from the oldest grandparent to the youngest sprig. Merkel turned for help to William Murrill of the New York Botanical Garden. By the following spring, Murrill had worked out the unknown fungus’s basic life cycle, including that it entered through bark wounds and could kill a mature tree in two to three years by girdling the trunk.

By August of 1906, nearly all the chestnut trees in the Bronx were affected, the fungus had spread into Brooklyn, and reports were arriving from other states. The airborne blight spread rapidly throughout the chestnut’s range, from Maine to Alabama and westward to Arkansas. The impacts were particularly hard on wildlife and the rural poor, who depended on the chestnut for everything from food (for both humans and livestock) to barn beams and coffin linings. Further destruction was caused by salvage logging, in which healthy — and possibly resistant — trees were chopped down for wood.

To fully understand the impact of this tragedy, it is worth noting that in some places the American chestnut accounted for one-quarter of the entire tree canopy; legend has it that a squirrel could travel the chestnut canopy from Georgia to Maine without ever setting foot on the ground. Its nuts were flavorful, nutritious and wildly abundant, with a reliably heavy annual crop unaffected by frost; it was said that a family that owned a chestnut tree would never go hungry.

If the tree was chopped down, it would rapidly re-grow from stump sprouts; a mature tree could reach approximately 100 feet tall and 10 feet in diameter. The wood was light, strong and easy to split; its beams still support many older buildings in New England today.

Efforts to restore the American chestnut to its former glory have, until recently, been arduous, slow and relatively ineffective. Between the 1930s and 1980, the U.S. Department of Agriculture (USDA) fruitlessly endeavored to crossbreed American and Chinese trees, hoping to combine the blight resistance of the smaller, shrubbier Chinese chestnut with the desired height and other wood characteristics of the American chestnut.

Just as the USDA’s program closed due to failure, Charles Burnham, a corn geneticist, realized that they had neglected to utilize a basic resistance-development technique called backcrossing. In backcrossing, the two parents (Chinese and American chestnuts) are bred, and then the offspring is bred back to a desired parent over generations, eventually eliminating undesired characteristics (e.g. shrubbiness) while retaining the desired characteristic (blight resistance).

After utilizing this technique for over 30 years, the American Chestnut Foundation has now released a limited quantity of backcrossed seeds, dubbed Restoration Chestnut 1.0, to the public.

In another effort, the American Chestnut Cooperators’ Foundation is attempting to breed an entirely American chestnut using resistant trees. Additionally, in what some may consider a more controversial approach, researchers at the State University of New York have bred a resistant tree by inserting a wheat gene; they hope to make this tree available to the public in the next few years.

Whichever of these approaches turns out to be most viable, some variation of the American chestnut is poised for a comeback. Of course, like most saplings, these trees are vulnerable to deer browse, ice damage and similar problems, but it does seem possible that American chestnuts will make a return to their native range. Perhaps your children, or grandchildren, someday will watch squirrels race up and down their furrowed bark.

Reeve Gutsell is a volunteer at the Hitchcock Center for the Environment. She has a master’s degree in Resource Management and Conservation from Antioch University, and a master’s degree in Creative Writing from Naropa University. She enjoys spending as much time as possible exploring the Pioneer Valley. For more information on breeding efforts, visit the American Chestnut Foundation’s website, www.acf.org, and the American Chestnut Cooperators’ Foundation’s site, accf-online.org.

Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 525 South Pleasant St., Amherst, appears every other week in the Daily Hampshire Gazette. For more information, call 413-256-6006, or write to us.

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