The pre-settlement forest vegetation of the Appalachians consisted of two broadly defined deciduous forest associations (oak-chestnut and mixed mesophytic) at lower and intermediate elevations and one subalpine coniferous association found at higher elevations. Because of the virtual elimination of American chestnut (Castanea dentata) by the chestnut blight fungus in the first half of the twentieth century, the oak-chestnut association is now best referred to as the mixed oak association. These forest associations occur in three physiographic provinces (Ridge and Valley, the Blue Ridge, and the Appalachian Plateaus) of the Appalachians. Various species of oak, especially northern red oak (Quercus rubra), chestnut oak (Q. montana), and white oak (Q. alba) along with several species of hickory (Carya spp.), are consistently present in the mixed oak association, and red spruce (Picea rubens) is the defining species of the subalpine coniferous association. The mixed mesophytic association is characterized by a diverse assemblage of trees, including sugar maple (Acer saccharum), American beech (Fagus grandifolia), black birch (Betula lenta), and Canadian hemlock (Tsuga canadensis). Each of these is considered in some detail in this chapter.