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The American chestnut (Castenea dentata) was once the dominant hardwood species in Appalachian mountain forests, comprising as much as 40 percent of the overstory trees in the climax forests of the Eastern United States. It has been said that an enterprising squirrel could once travel from Maine to Georgia on the interlocking branches of chestnut trees. Visitors traveling toward the Appalachians from the coast could be fooled into thinking that the mountain peaks were snow covered when the chestnuts bloomed white in June. The fast growing American chestnuts often reached five feet in diameter and 60 to 100 feet in height. The trees were an extremely important source of food for wildlife including squirrels, wild turkeys, deer, bears and the now extinct passenger pigeon. The demise of the trees also brought reductions in the populations of wildlife that depended on chestnuts. Nevertheless, as important as the American chestnut was to the food chain, its loss did not lead to massive animal extinctions as some feared it might. Seven species of butterflies that fed on chestnuts exclusively are thought to have gone extinct. Fossilized pollen indicates that chestnut trees had lived in North America for 40 million years.
The chestnut tree was greatly valued by pioneers for both its nuts and its straight, rot resistant lumber. The wood was easily worked and very useful for constructing long-lasting buildings and fences. Chestnut bark was a rich source of the tannins used to tan leather. Chestnuts have been called “the rice that grows on trees” because they have essentially the same nutritional profile as brown rice. Containing only 1% to 2% fat content, chestnuts are unique among nuts.
Then in 1904 disaster struck. That year forester Herman Merkel noticed that the American chestnut trees that lined the avenues of the Bronx Zoo were dying. The Asian chestnut blight (Cryphonectria parasitica) had arrived and began to spread rapidly. The blight fungus was probably brought to America on imported nursery stock of Chinese chestnuts. American trees had simply never evolved resistance to this parasite.
The chestnut blight fungus spreads by spores that can be carried by the wind, birds, small animals and humans. The fungus invades trees at breaks in the bark or where dead branches are attached to the main trunk of a tree. The blight appears as an orange canker on the trunk of a tree. Once established the fungus rapidly "girdles" the infected tree, cutting off water and nutrients to the parts of the tree above the site of the infection. It can kill a large tree within 18 months after the infection begins. Chestnuts still survive in Eastern forests as sprouts that grow from the roots of dead trees. These sprouts can reach 15 feet in height before they become infected. While these sprouts occasionally produce nuts, they are not enough to sustain a population of American chestnuts in wild over the long run.
After its discovery in 1904, the blight spread rapidly at about 20-50 miles per year. By 1950, the blight had devastated 9 million acres of forests by killing several billion American chestnut trees. The species was essentially exterminated from Eastern U.S. forests. For the most part, the previous oak-chestnut forests have now become oak forests or oak-hickory forests.
The danger posed by the blight was immediately recognized but all attempts to halt its spread failed. In one such attempt, the state government of Pennsylvania created a mile wide "firebreak" hoping to stop the onslaught. It is possible that American trees that might have had natural resistance were destroyed in the panic engendered by the spreading blight as owners cut down their trees before they could be ruined. The U.S. Department of Agriculture and the Connecticut Agricultural Experiment Station began breeding programs to try to create a blight resistant American chestnut. But neither program was able to create a tree that combined blight resistance with the desirable traits of the native tree. The USDA abandoned its breeding program in 1960 and the Connecticut Station stopped in 1970. It looked like the American chestnut was doomed.