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The American
Chestnut Still Lives in Tennessee
by
Joe Schibig
Before the chestnut blight struck in the 1930s and 1940s, millions of stately American chestnut trees dominated the upland forests of Tennessee, especially in the eastern mountains. The relentless blight destroyed practically every standing American chestnut in the state, but some of the trees did not completely die. The blight did not directly kill the roots, so some trees sprouted repeatedly from the root collar only to be killed again and again by the blight. Even though some diehard chestnuts have repeated this cycle of death by blight and resprouting numerous times since the 1940s, they cannot be expected to continue this forever. In addition to the blight, the chestnut has other enemies such as fire, root rot, insects, deer, cattle, and bulldozers. Although small sprouts are plentiful in the mountains, they become rarer as one travels westward in our state. Large flowering trees are very rare everywhere throughout the original range of the chestnut.
The notorious blight was probably brought over unknowingly on Asiatic chestnuts in the 1800s, but was first noticed in New York in the early 1900s; then it quickly spread southward and eventually killed billions of chestnuts throughout its former range. Only a handful of old trees are alive today that were actually standing when the initial wave of blight swept through the eastern U. S. There is a big survivor in Amherst County, Virginia and another one still lives in Adair County, Kentucky. I have seen no American chestnut tree in Tennessee that definitely was a mature tree when the initial blight swept through our state; however, there is a large American chestnut, approximately 60 years old, in Jackson County, Tennessee which is 55 feet tall and two feet in diameter at breast height. Our native chestnuts had little resistance against this exotic parasitic fungus that eats away at the inner bark until it girdles and kills the tree.
Before the blight, giant chestnut trees over 5 feet in diameter and approaching 100 feet in height were not uncommon. A few long-lived trees in the mountains developed diameters greater than 10 feet and stood over 100 feet tall. It was the most important timber tree in the mountainous areas of Tennessee; in some places it formed nearly pure stands. The durable rot-resistant wood had many uses—fence posts, railroad ties, utility poles, logs for barn and house construction, framing lumber, shingles, paneling, siding, furniture, pulpwood, fuel, and it was an important source of tannic acid. Elderly country folk recall the value of this great tree. They remember the split rail fences and the bountiful sweet nuts that fed wildlife, farm families, and their livestock; they recall the creamy white chestnut flowers that bloomed in June and remember visions of distant mountains which looked as if they were snow-covered because so many chestnut trees were cloaked with their creamy white flowers. The loss of the chestnut was a terrible blow, especially to poor mountain people, because it happened during the Great Depression, a time when they needed the tree the most. This was one of the greatest ecological disasters of the 20th century.
Prior to the blight, the American chestnut was abundant and made its best growth in the cove and slope forests of the Appalachian Mountains. Westward, it was a dominant tree in many of the forests of the Ridge and Valley, the Cumberland Plateau, and the Highland Rim regions. Chestnut never was important on the thin limestone soils of the Nashville Basin and its numbers tapered off west of the Tennessee River. It shunned the floodplains or other poorly drained areas. Today, American chestnut sprouts are found primarily on upland sites where the soils are acidic, deep, gravelly and/or sandy. Typically they are found with chestnut oak, black oak, scarlet oak, sourwood, and red maple; often they are associated with such shrubs as blueberry bushes an mountain laurel. Prior to the blight, chestnut was a dominant species on diverse sites including well-drained, moist sites, but today, our data from the Highland Rim region indicate that it competes best on the drier, open-canopy sites.
Unfortunately, the American chestnut’s only significant mode of reproduction has been its sprouting from the root collar, a form of asexual reproduction. This has kept chestnuts alive for 60 years or so since the blight. Chestnut sprouts usually are zapped by the blight before they attain 15 years of age. Although they produce both male and female flowers, chestnut trees seldom self-pollinate. They require another tree in close proximity for effective cross-pollination and since they rarely live long enough to flower these days, the flowering trees are usually isolated. Such trees produce burs, but the nuts are infertile. Evolution of American chestnuts toward blight resistance in Nature may not occur because there are hardly any sexually reproducing (seed producing) trees. Biologists will tell you that without sexual reproduction, the chances of native chestnuts naturally evolving blight resistance are equivalent to the chances of snowflakes in Hades evolving melt resistance.
Following the wholesale destruction of billions of American chestnut trees from the blight, plant breeders crossed blight-resistant Chinese chestnuts with pure American chestnuts. The F1 hybrids showed only moderate resistance to blight, not the full resistance of the Chinese parent, and they usually looked and grew more like the Chinese chestnut than the American chestnut. This was disappointing because the hybrids usually did not compete well in the forest—they did not grow tall and straight like the native American chestnut trees.
There are two foundations that are actively trying to breed blight-resistant strains of the American chestnut. The American Chestnut Cooperators Foundation (ACCF; website at: http://www.accf-online.org/) is striving to perfect blight-resistant chestnut trees by intercrossing pure American chestnut trees that have demonstrated some level of resistance. The ACCF was established by Dr. Gary Griffin and others. The American Chestnut Foundation (TACF; website at: http://www.acf.org/) is trying to develop numerous strains of blight-resistant American chestnut trees which will be adapted to different parts of the eastern U. S. and southern Canada. To achieve this, TACF is using the backcross method envisioned by the late Dr. Charles Burnham, a geneticist at the University of Minnesota. Dr. Fred Hebard at the Meadow View research farms in Virginia has been the chief plant breeder for TACF. He and others took Chinese chestnut trees, resistant to the blight, and crossed them with pure American chestnut trees, producing trees that were 50% American and 50% Chinese. These trees were then backcrossed to the American species, producing trees that were 75% American. The backcrossing procedure was repeated two more times and produced trees with at least 94% American genes. Each generation was tested for blight resistance and only the most resistant trees were used as parents for the next backcross. These predominantly American hybrids are being intercrossed to produce American chestnut trees that show no obvious Chinese characteristics other than blight resistance. TACF expects to have the first seeds of blight resistant, predominantly American trees available to the public within 10 years. This foundation with its several state chapters and thousands of volunteers has come a long way in just 25 years.
Most of the native Tennessee chestnut trees being used in the TACF breeding program occur on the Highland Rim of middle Tennessee or on outliers of the Rim in the Outer Nashville Basin. The largest and most impressive are found on the northeastern section of the Highland Rim. The state record for overall size “proudly” stands near the summit of a high ridge in Jackson County close to Gainesboro. This old warrior of a chestnut has fought the blight for many years as evidenced by the swollen cankers along its trunk. Only a few American chestnut trees in the country are of this size and age. It may be that these survivors attain old age and large size because the strains of the blight fungus attacking them are hypovirulent--weakened by a virus (a viral parasite on the fungal parasite). Chestnut experts (Dr. Griffin and Dr. Hebard) have also suggested that these large survivors may have a low level of blight resistance and are growing on sites favorable for their growth and survival. On the Highland Rim, most of these older chestnut trees are growing on relatively dry sites where the tree canopy is open. Another beautiful chestnut which was pollinated by TACF volunteers in June, 2003 grows vigorously on a wooded ridge in Clay County, Tennessee, close to the Red Boiling Springs community. This tall and straight chestnut towers to 65 feet and has a diameter of 12 inches at breast height. Remarkably, it is blight-free; however, it is probable that it is blight susceptible, but has thus far been lucky enough to escape infection by the blight fungus. Blight spreads as spores are blown by wind from an infected chestnut tree to other trees. Insects and birds, especially woodpeckers, are also agents of spore dispersal. The quantity of blight-producing spores in the environment is probably much less now than it was during the pandemic years when so many trees were infected and shedding the lethal spores. Even if all chestnut trees disappeared, the blight fungus would live on in oak trees, especially the post and scarlet oaks.
Some of the best potential mother trees are located on steep slopes such as the tall chestnut in Davidson County, Tennessee and the big tree on a wooded bluff overlooking Kentucky Lake at Land Between the Lakes. Since a bucket truck or ladder is out of the question on such sites, the best way to pollinate these trees is by having professional arborists (tree climbers) get up into the tree and apply pollen to the female flowers; the climber also puts a bag around the pollinated flowers to prevent pollination from the wrong source and to protect the developing nuts from squirrels and chestnut weevils. The arborists return to the trees in the fall to remove the bags and harvest the precious nuts.
We are currently inventorying American chestnut trees in Middle Tennessee and South Central Kentucky and are especially interested in locating the larger trees (over 4 inches in diameter at breast height) but we are recording data on the smaller ones as well. If you know of the locations of pure American chestnuts, not Chinese chestnuts or hybrids, in Tennessee or Kentucky, please contact the author (jschibig@volstate.edu). To learn how to distinguish pure American chestnuts from Asiatic chestnuts go to: http://www.cnr.vt.edu/dendro/comparison/ . To see other American chestnut photos and learn more about this magnificent tree please visit: http://www2.volstate.edu/jschibig/resurrectingthechestnut.htm
Joe Schibig is a professor of biology at Volunteer State Community College and has studied the forest communities of south central Kentucky and north central Tennessee for 30 years.