Forest ecosystems are subjected to many biotic and abiotic stresses. Native insects and diseases, droughts, windstorms, and wildfire periodically impact forests or specific tree species, leaving dead or weakened trees.
The effects of these stresses may be manifested locally or over a larger area, however they do not cause species extinction.
In contrast, foreign pests can threaten the continued existence of a tree species. This because tree species
have not evolved genetic resistance to non-native pests, as the coevolutionary processes have not occurred.
Three prominent North American tree species, American chestnut (Castanea dentata ((Marsh.)) Borkh.), butternut (Juglans cinerea L.),
and American elm (Ulmus americana L.) have been severely impacted by three non-native fungal diseases, chestnut blight (Cryphonectria parasitica), butternut canker (Sirococcus clavigigenti-juglandacearum),
and Dutch elm disease (Ophiostoma u1mi and O. nova-ulmi).
Chestnut blight is a fungus that has virtually wiped out the American chestnut, as a commercial species, from eastern hardwood forests. Although roots from trees cut or killed many years ago continue to produce sprouts
that survive to the sapling stage before being killed, there is no indication that a cure for this disease will be found. The fungus is widespread and continues to survive as a nonlethal parasite on chinkapin,
Spanish chestnut, and post oak.