At the end of the nineteenth century, the American chestnut was a major component of eastern deciduous forests from Maine to Georgia and west to Illinois, in some places constituting more than 40% of overstory trees (Krebs 1985). Early in the twentieth century, chestnut blight, a nonindigenous fungal disease from Asia, broke out near New York City and quickly spread and infected almost all American chestnuts on the continent, driving the species to ecological extinction. American chestnuts now exist only as scattered small trees that become infected and die as they mature.

Because the American chestnut was such a prominent component of eastern deciduous forests, the nonindigenous fungal disease has had far-reaching effects. Although no vertebrates became extinct because of the loss of American chestnuts, seven moth species fed exclusively on American chestnuts and are now extinct (Opler 1978). Another 49 moth species also feed on American chestnuts, but because of broader diets, they are able to feed on related trees and shrubs, including the introduced Chinese chestnut. The structure of the forests significantly changed because of the blight, and other tree species became dominant.