Fire Ecology and Management of Oak-hickory Forests

The oak-hickory forest type (Braun 1950, Barrett 1994) occurs primarily on average to dry upland sites throughout the central hardwood region. The dominants typically are white oak (Quercus alba), northern red oak (Quercus rubra), mockernut hickory (Carya tomentosa), pignut hickory (Carya glabra), black oak (Quercus velutina), yellow poplar (Liriodendron tulipifera) and occasionally, white pine (Pinus strobus) (Schafale and Weakley 1990). In the Southern Appalachians, oak-hickory forests are found at low elevations on sites less exposed than oak-pine forests and more exposed than cove forests. Depending on disturbance history, oak-hickory can also be found on moist upland sites.

Fire has been a vitally important disturbance agent influencing the structure and composition of this forest type. Oak-hickory forests historically had an understory fire regime (Van Lear and Waldrop 1989).  Native Americans burned these forests frequently to promote grasses and attract game, among other reasons. Although precise presettlement fire frequencies are not known, conservative estimates suggest fire return intervals of 2.8 years (Cutter and Guyette 1994) to 14 years (Buell and others 1954, Guyette and Day 1997).  These frequent Indian fires likely maintained oak-hickory forests as barrens, prairies and oak savannas before European contact. Oaks and hickories were favored by these frequent fire regimes, because they both have adaptations that make them resistant to fire, such as thick bark. As a result, these species dominated the canopy as old, large, fire-resistant trees. Shrubs, understory trees, and woody debris were likely rare in these fire-maintained forests. 

When Native American populations were decimated by new diseases after European contact, the frequency and extent of fire decreased substantially throughout the South and grasslands, savannas, and woodlands succeeded to closed forest. Subsequent settlement of the oak-hickory forests by Euro-Americans did increase fire frequencies to some extent, since these early settlers used fire for many of the same reasons as the Native Americans. However, fire suppression activities in the 1900s decreased fire frequency once more in oak-hickory forests, as they did throughout the South.  Presently, the fire regime of oak-hickory forests is characterized by very infrequent, low-intensity surface fires.

These altered fire regimes have profoundly changed the oak-hickory forest by allowing it to succeed to mixed mesophytic and northern hardwood species such as red maple, eastern white pine, sugar maple, and beech. On drier mountainous sites, fire exclusion allows ericaceous shrubs such as mountain laurel and rhododendron to move from riparian areas into upland forests (Elliott and others 1999). Although the forest floor rarely dries enough to support surface fire, this ericaceous shrub layer is flammable; and when it burns, it typically supports intense, stand-replacement fires that alter successional pathways, reduce site productivity, negatively impact streams, and threaten human life and property.

Until recently, land managers failed to appreciate the role of prescribed fire in restoring and maintaining open oak-hickory forests (Lorimer 1993). However, research indicates that fire can be used in hardwood stands to establish and release oak-hickory regeneration (Barnes and Van Lear 1998, Brose and Van Lear 1998, 1999, Christianson 1969).