The American chestnut (Castanea dentata) was once one of the dominant trees of eastern North American forests. A bark fungus (Cryphonectria parasitica), the causative agent of a disease known as chestnut blight and accidentally introduced into North America from Asia early in the 20th century, almost caused the tree become extinct. The species still survives, however, and there are now efforts to breed trees more resistant to the killer fungus.
I photographed this American chestnut tree suffering from blight in Seneca Creek State Park in Gaithersburg, Maryland about 10 days ago.
This is what the sign says.
Apparently, chestnut blight kills the main trunk, but the roots survive and new shoots often sprout from around the roots. That was exactly what was happening in this case.