Physiognomy and Structure: This alliance is characterized by an open evergreen canopy with or without a component of deciduous trees, a tall-shrub layer of shrub oak, and a low heath layer. The herbaceous layer varies in cover with degree of cover of the heath or scrub oak layer.

Floristics: This alliance is dominated by Pinus rigida, usually characterized by a well-developed tall-shrub layer dominated by Quercus ilicifolia overtopping a low heath layer comprising Vaccinium angustifolium, Vaccinium pallidum, and Gaylussacia baccata. The herbaceous layer is usually patchy, but is better developed where the shrub layer is less dense. Characteristic herbs include Carex pensylvanica, Cypripedium acaule, Danthonia spicata, Gaultheria procumbens, Melampyrum lineare, and Pteridium aquilinum. Associated tree species may include Pinus strobus, Quercus alba, Quercus rubra, Quercus velutina, Sassafras albidum, and at the northern range limit, scattered Picea rubens and Abies balsamea. Other shrub species that are often present include Comptonia peregrina, Kalmia angustifolia, Aronia melanocarpa, and Quercus prinoides. Additional herbaceous associates may include Comandra umbellata, Helianthemum canadense, Piptatheropsis pungens (= Oryzopsis pungens), and Schizachyrium scoparium.

Dynamics:  Fire is an important ecological process in both habitats, but on the most extreme sites, this vegetation is maintained by topo-edaphic conditions.