American Chestnut - History and Restoration Efforts in Virginia

The American chestnut, Castanea dentata (Marsh.) Borkh., was once a common dominant tree in the deciduous forests of eastern North America. In some parts of the Appalachians it was estimated to comprise 25% of the timber volume.

The chestnut had many valuable properties. Its wood was easily split, easily worked, and highly rot-resistant. Tannins from the bark and heartwood were the best available for tanning heavy leathers. A consistent production of annual nut crops, in contrast to the sporadic acorn crops of oak, made the chestnut an important food source for man and wildlife. Even-aged stands at village sites suggest that chestnut was planted and cultured by Native Americans.

The chestnut tree was relatively fast-growing and had a strong sprouting ability. It was capable of growing from moist cove sites to dry ridge tops, although it was most common on side slopes intermediate in soil moisture.

The chestnut blight, caused by the fungus Endothia parasitica, was first reported in New York in 1904. Within 50 years it had spread throughout the natural range of chestnut. Virtually all chestnut trees were killed by the blight.

However, two forms of evidence exist today attesting to the past importance of chestnut. The rot resistance of chestnut wood allows one to still find chestnut stumps and snags throughout the natural range. Even more would be evident except for a salvage industry in chestnut wood that lasted a couple of decades after the blight epidemic.

More importantly, the sprouting ability of chestnut remains and chestnut sprout clumps are fairly common in the mountains. Rarely do the sprouts attain much size before succumbing again to the blight.

Hope for the future of chestnut rests in two sources, genetic resistance and weakened strains of the blight organism (hypovirulence).

Genetic Resistance: The Backcrossing Program

A few large remaining trees survive at scattered locations in the natural range. All are infected by the blight to some degree. None exhibit a high degree of resistance.

In contrast, Chinese chestnut (Castanea mollissima) has a high degree of resistance. Chinese-American (CxA) hybrids have an intermediate level of resistance. Work is underway in several states to backcross American trees to Chinese-American hybrids. After three backcrosses, cross-pollination of the backcross population will result in trees that are 15/16 American in genetic makeup but have the high resistance of the Chinese species.

Success in this program is twenty to thirty years away.

Hypovirulence

The chestnut blight attacked the European chestnut (Castanea sativa) in Italy in the 1930’s and spread throughout Europe. In 1953 an Italian researcher noticed that all the cankers at a site in northern Italy were healing. Strains of the fungus were isolated from these trees that were weaker in their parasitic effects (hypovirulent). A virus-like organism infecting the fungus has been identified as the cause. Hypovirulence has allowed the Europeans to once again culture orchards of European chestnuts.

Hypovirulence has been found in North America. However, it has not spread here near as effectively as in Europe. A hypovirulent strain must be vegetatively compatible with a virulent strain in order for the conversion to occur. Hypovirulence is probably a factor in the survival of many of the large, living American trees.

Restoration Efforts In Virginia

Dr. Fred Heberd of the American Chestnut Foundation is directing backcrossing and other efforts at the Meadowview Farm in Wytheville, Virginia.

Dr. Gary and Mrs. Lucille Griffith, of the American Chestnut Cooperators Foundation, work with hypovirulence and breeding from Newport, Virginia.

The Virginia Department of Forestry works with backcross breeding at its Lesesne State Forest in Nelson County. The Department is also establishing a clone bank at its New Kent Forestry Center in Providence Forge, Virginia.