Death of the American Chestnut

Is an American Chestnut Comeback Possible?

american chestnut tree
Isolated American Chestnut in Nebraska. (Steve Nix)

Glory Days of American Chestnut

American chestnut was once the most important tree of the Eastern North American Hardwood Forest. One fourth of this forest was composed of native chestnut trees. According to a historical publication, "many of the dry ridge tops of the central Appalachians were so thoroughly crowded with chestnut that, in early summer, when their canopies were filled with creamy-white flowers, the mountains appeared snow-capped."

The Castanea dentata (scientific name) nut was a central part of eastern rural economies. Communities enjoyed eating chestnuts and their livestock was fed and fattened by the nut. The nuts not consumed were sold if a market was available. Chestnut fruit was an important cash crop for many Appalachian families that lived near rail hubs. Holiday chestnuts were transported to New York, Philadelphia and to other big-city dealers who sold them to street vendors who sold them fresh-roasted.

American Chestnut was also a major lumber producer and used by home builders and woodworkers. According to the American Chestnut Foundation or TACF, the tree "grew straight and often branch-free for fifty feet. Loggers tell of loading entire railroad cars with boards cut from just one tree. Straight-grained, lighter in weight than oak and more easily worked, chestnut was as rot resistant as redwood."

The tree was used for nearly every wood product of the day - utility poles, railroad ties, shingles, paneling, fine furniture, musical instruments, even paper.

The American Chestnut Tragedy

A devastating chestnut disease was first introduced in North America from an exported tree to New York City in 1904.This new American chestnut blight, caused by the chestnut blight fungus and presumably brought in from eastern Asia, was first found in only a few trees in the New York Zoological Garden.

The blight rapidly spread to northeastern American forests and in its wake left only dead and dying stems in what was a healthy chestnut forest.

By 1950, American chestnut had tragically disappeared except for shrubby root sprouts the species still continually produces (and which also quickly become infected). Like many other introduced diseases and insect pests, the blight quickly spread. The chestnut, being completely defenseless, faced wholesale destruction. The blight ultimately invaded every tree throughout the entire range of the chestnut, where now only rare remnant sprouts are found.

But with these sprouts bring some hope of reestablishing American chestnut.

For decades, plant pathologists and breeders have tried to create a blight-resistant tree by crossing our own species with other chestnut species from Asia. Native chestnut trees also exist in isolated areas where the blight is not found and are being studied. 

Restoring the American Chestnut

Advances in genetics have given researchers new directions and ideas. Working and understanding the complex biological processes of blight resistance still need further study and improved nursery science.

TACF is a leader in American chestnut restoration and confident that "we now know we can have this precious tree back." 

In 1989, The American Chestnut Foundation established the Wagner Research Farm. The purpose of the farm was to continue a breeding program for ultimately saving the American chestnut. Chestnut trees have been planted at the farm, crossed, and grown at various stages of genetic manipulation.

Their breeding program is designed to do two things:

  1. Introduce into the American chestnut the genetic material responsible for blight resistance.
  2. Preserve the genetic heritage of the American species.

Modern techniques are now being used in restoration, but success is measured in decades of genetic hybridization. An elaborate and time-consuming breeding program of backcrossing and intercrossing new cultivars is TACF's plan to develop a chestnut that will exhibit virtually every Castanea dentata characteristic.

The ultimate desire is a tree that is fully resistant and, when crossed, the resistant parents will breed true for resistance.

The breeding method began by crossing the ​Castanea mollissima and ​Castanea dentata to obtain a hybrid which was one-half American and one-half Chinese. The hybrid was then crossed to another American chestnut to obtain a tree which is three-fourths dentata and one-fourth mollissima. Each further cycle of backcrossing reduces the Chinese fraction by a factor of one-half.

The idea is to dilute out all of the Chinese chestnut characteristics except for blight resistance down to where trees are fifteen-sixteenths dentata, one-sixteenth mollissima. At that point of dilution, most trees will be indistinguishable by experts from pure dentata trees.

Researchers at TACF report that the process of seed production and testing for blight resistance now requires about six years per backcross generation and five years for intercross generations.

Says TACF about the future of a resistant American chestnut: "We planted our first set of intercross progeny from the third backcross in 2002. We'll have progeny from the second intercross and our first line of blight resistant American chestnuts will be ready for planting in less than five years!"

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Nix, Steve. "Death of the American Chestnut." ThoughtCo, Apr. 12, 2017, thoughtco.com/death-of-the-american-chestnut-1341837. Nix, Steve. (2017, April 12). Death of the American Chestnut. Retrieved from https://www.thoughtco.com/death-of-the-american-chestnut-1341837 Nix, Steve. "Death of the American Chestnut." ThoughtCo. https://www.thoughtco.com/death-of-the-american-chestnut-1341837 (accessed December 15, 2017).