According to David Vandermast
Chestnut blight was caused by a fungus eventually determined to be Cryphonectria parasitica. It was probably imported to the United States on the Chinese or Japanese species of the tree, which both show resistance to it. The blight destroyed billions of American chestnut trees in the first half of the 20th century. The loss of the chestnut, in terms of the sheer number of trees killed, the size of its range before the blight, and the variety of habitats affected by its demise, is unrivaled in the history of human-wrought ecological disasters, even though epidemics such as Dutch elm disease have received more attention.
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