The American chestnut (Castenea dentata) was widespread across eastern North America until the early 1900s. It was one of the most important trees of the eastern hardwood forest and made up almost half of the population of trees in central and southern Pennsylvania, New Jersey, and southern New England. In its entire range, the species dominated the deciduous forests, making up almost one quarter of the trees. The fungus Cryphonectria parasitica, commonly known as the chestnut blight, caused the near extinction of the American chestnut tree in North America. Through ongoing genetic studies and improvements in plant breeding techniques, the American Chestnut Foundation is working to restore this tree to its native range within the woodlands of the eastern United States.