Fire Ecology and Management of Xeric Oak-pine Forests

Oak-pine forests occupy dry sites throughout the Southern Appalachians, typically exposed ridges and south and west facing slopes.  The canopy trees of this community include xerophytic oaks (scarlet oak (Quercus coccinea) and chestnut oak (Quercus prinus)) and yellow pines (pitch pine (Pinus rigida), short-leaf pine (P. echinata) and Virginia pine (P. virginiana)). Understories are commonly evergreen shrubs and herbs. At extremely dry sites, oak-pine forests gradually change into pine-heath forests dominated by Table Mountain pine, virginia and pitch pines. 

Fire was historically very important in the distribution and composition of xeric-oak pine forests in the southern Appalachians (see: Fire regimes of oak-pine forests).  It is unclear, however, what fire regime was typical of this forest type.  Some sources suggest that native American burning maintained pitch pine as an understory fire regime type, with a 2- to 10-year fire interval (Wade and others 2000).  However, these communities often intermix with Table Mountain pine, which is believed to have had a fire regime of higher-intensity, stand-replacement fires.  In fact, in other areas of its distribution, pitch pine is typical of ecosystems that experience high-intensity fires at intervals of 10-30 years (Christensen 1981).  Despite this uncertainty, however, it is generally believed that fires set by native Americans maintained these stands with relatively large pines, scattered smaller pines and oaks, and a sparse understory of low ericaceous shrubs and herbs (Little 1946, 1973). 

The yellow pine species native to the oak-pine forest of the southern Appalachians show various degrees of fire adaptation. For example, pitch pine has serotinous cones (Fowells 1968), thick bark, dormant buds along the bole (Zobel 1969), and develops a basal crook in seedlings (Little and Mergen 1966). Shortleaf pine also shows a degree of cone serotiny and develops a basal crook in seedlings (Little and Mergen 1966). Virginia pine shows fewer specific adaptations to fire than either pitch or shortleaf pine, yet like these species it is a shade-intolerant species that requires exposed mineral soil surfaces and full sunlight for its regeneration (USDA Forest Service 1965).  Therefore, these pines species are not only fire tolerant, but they require fire or other disturbance for their regeneration.  Table mountain pine is one of the most fire-dependent pine species of the southern Appalachians, often requiring moderate to high intensity surface and crown fires to open their serotinous cones (Zobel 1969; Barden 1978; Sanders 1992).

Although oak species are not dependent on fire for regeneration as are some species of pines, oaks are well adapted to an environment that includes periodic fire. Oak species have several biological adaptations that enhance their ability to survive on sites exposed to frequent fire, including: high resprouting capacity, thick bark, and resistance to rotting after scarring. Frequent fires also give oaks several regeneration advantages over competing species, such as: preparing seedbeds and encouraging acorn caching; discouraging acorn and seedling predators; reducing fire-intolerant competitors; and xerifying sites by removing the forest floor and opening the canopy (See: Fire and Oaks).

During the fire suppression era of the 1900s, fire was essentially removed as a disturbance agent across the southeast.   For example, the creation of the Great Smoky Mountains National Park (GSMNP) in the 1930s altered fire frequencies from once every 10-40 years (from the period of 1856-1940) to once every  2000+ years (Harmon 1982). The altered fire regimes had profound impacts on landscapes in the southern Appalachian region, and in particular, resulted in a decline of oak-pine forests. In the absence of periodic fire, forest succession has allowed hardwood species and white pine (Pinus strobus) to invade areas previously dominated by yellow pines on mid-elevation, southwest facing slopes. The loss of oak from these stands has negative implications on wildlife, since acorns are an important food source for black bear, white-tailed deer, wild turkey, and other wildlife species. The decreased herbaceous abundance and diversity cause by fire suppression also has had negative impacts on wildlife.  Today, these oak-pine forests are characterized by increased density and biomass of mountain laurel in the shrub layer and heavy fuel loads in the forest floor.  These structural shifts put these forests at risk of catastrophic fires.

In recent years, prescribed fire has been advocated as a tool to restore oak-pine communities in the Southern Appalachians. Due to the hazards of using fire in steep topography and the susceptibility of these soils to erosion, prescribed fire is far less common in the Southern Appalachians than in the Coastal Plain and Piedmont. Consequently, little information is available on the appropriate frequency, intensity and season fires should be prescribed for ecological restoration. However, some information is starting to accumulate, as federal land managers reintroduce prescribed fire on federally owned lands.  For example, there is some evidence suggesting that low-intensity restoration burns can be used without significantly altering ecosystem pools and cycling rates of carbon and nitrogen in xeric oak–pitch pine communities (Knoepp and Swank 1993; Vose et al. 1999) and shortleaf, oak–pine community types (Hubbard et al. 2004).  Also, low-intensity prescribed burns are unlikely to cause soil erosion if conducted under the correct conditions.