Forests in the Appalachians and Ozarks are subject to a variety of threats. These threats can involve the forests as a whole or just certain species or groups of tree species or other plants. Many of these threats emerge as a result of the introduction, inadvertent or intentional, of plants, insects, or fungi not native to the two regions. Among the most noted examples was the introduction of the chestnut blight fungus. This fungus essentially eliminated American chestnut (Castanea dentata) from the forest canopy in the Appalachians and Ozark chinquapin from the forests of the Ozarks. The purpose of this chapter is to describe various other threats—past, present, and potential—to the forests of the Appalachians and Ozarks.