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.  

Anthropogenic fire regimes that characterized the southern Appalachian landscape began to change with the settlement of Europeans in the 16th century.  European settlement had a devastating effect on the Native American population, and indirectly decreased the influence of anthropogenic fires. Native Americans of the l6th-18th centuries continued to influence landscape conditions, albeit on a much smaller scale. Despite this decrease in fire set by native Americans, anthropogenic fires still affected the Southern Appalachians to a large extent during the 1700-1800s since the European settlers that moved into the region during that time adopted the firing practices of the Indians (Pyne 1982). It wasnt until the fire suppression era of the early 1900s that fire was essentially removed as a vector for shaping landscapes in the southern Appalachian region. 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).

Effects of fire suppression on oak-pine forests

The highly effective fire suppression programs of the 1900s resulted in a decline of oak-pine forests throughout the southern Appalachian region. Once vast areas of open oak-pine forests in the Great Smoky Mountains National Park (GSMNP) are essentially non-existent today (SAMAB 1996e).   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 upper elevation, southwest facing slopes. This process has affected two rare forest communities in particular, mountain longleaf pine woodlands and Table Mountain pine/pitch pine woodlands (SAMAB 1996e). In recent years, the pine component of these stands has been furtHer reduced by drought and associated southern pine beetle infestations (Smith 1991). Many oak-pine forests are slowly degrading into poorly stocked stands with dense understories dominated by mountain laurel (Clinton et al. 1993, Swift et al. 1993, Vose and Swank 1993, Clinton and Vose 2000).

While oaks may withstand the absence of fire better than yellow pines, even they loose their competitive ability against shade tolerant and fire intolerant species such as soft maples, white pine, and sourwood (SAMAB 1996e), particularly on more mesic sites.  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.  

Due in part to fire suppression, most oak-pine ecosystems in the southern Appalachians today are characterized by high overstory mortality and slow growth rates, inhibited regeneration of overstory species, increased density and biomass of mountain laurel in the shrub layer, heavy fuel loads in the forest floor, decreased herbaceous abundance and diversity, and increased susceptibility to insect infestations (Vose 2000). Due to these structural shifts, fire exclusion has increased the likelihood of catastrophic fires in forest ecosystems more adapted to low-severity and -intensity fire. Failure to restore some of these fire-dependent communities will likely result in their permanent loss as ecosystem components since extensive areas that once supported these communities are without a seed source needed for their reestablishment (Buckner and Turrill 1999). 

Fire has played a major role in the dominance of pitch (Pinus rigida) and Virginia pines (Pinus virginiana).  These pines, which typically dominate south- and west facing slopes in the Southern Appalachians, make up major components of the xeric-oak pine and pine heath communities of this region.  Both pines characteristically grow on poor sites, with generally sandy, gravelly, or shallow soils. 

Silvical characteristics of pitch pine suggest it is well adapted to fire. It has thick bark and the ability to refoliate from dormant buds located along the stem and branches, or from the basal crook located just below ground line (Little 1979). Moreover, a majority of the trees have serotinous cones especially where fires are severe (Little 1974).  Seed is also produced at an early age, 3 to 4 years for sprouts and 10 years for seedlings (Little 1953).  Due to its thin bark, Virginia pine is less tolerant of fire than pitch pine, although basal sprouting and seed production at a young age does offer this species degree of fire tolerance.

Historically, mixed severity fires were probably prevalent over much of the range of pitch and Virginia pines. Native American burning maintained pitch pine using an understory fire regime type, with a 2- to 10-year return interval (Wade and others 2000). This frequency maintained stands with relatively large pines, scattered smaller pines and oaks, and sparse understory of low ericaceous shrubs and herbs (Little 1946, 1973). Due to its higher tolerance to fire, the importance of pitch pine in stands likely increased relative to Virginia pine with increasing fire frequency.  Although the historical fire regime in Virginia pine is unknown, it was likely less frequent and resulted in higher mortality than that of pitch pine.

Today, altered fire regimes have increased fire return intervals in the xeric-oak pine and pine heath communities where pitch and Virginia pine occur. In the absence of fire, these yellow pines are usually outcompeted by hardwood species or eastern white pine. On upland sites, trees usually invade much faster than understory shrubs such as huckleberries and blueberries (Little 1979; Little and Moore 1949). On more mesic sites, fire exclusion leads to replacement by red maple, blackgum, sweetbay, American holly, and dense shrub understories (Little 1979).

In order to restore community composition of these oak-pine forests in the Southern Appalachians, the use of prescribed fire has been advocated by federal and state agencies (Swift and others 1993; Vose and others 1994, 1997). Due to the hazards of using fire in steep topography and the susceptibility of these soils to erosion, the use of prescribed fire in this area is rare relative to its use in the coastal plain. Consequently, little information is available on the appropriate frequency, intensity and season fires should be prescribed for ecological restoration; comparably more information is available on the silvicultural uses of fire in pitch and Virginia pine.    

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 reprouting capacity, thick bark, resistance to rotting after scarring, and rapid acorn germination on fire-prepared seed beds. 

Perhaps the most notable of these adaptations is the generas high resprouting capacity following fire (Johnson 1993).  Oak species have a concentration of dormant buds near the root collar. These buds often remain an inch or more below the soil surface where they are protected from lethally high temperatures (Korstian 1927).  Also, sprouts arising from belowground buds tend to have fewer pathogens and therefore have higher survival than aboveground sprouts (Roth and Hepting 1943).  This tenacious ability of small oak rootstocks to resprout repeatedly following frequent top-kill enables oak to dominate the advanced regeneration pool in areas where fire occurs at frequent intervals.  For example, resprouting has been reported in many studies as a key mechanism maintaining survival of oak seedlings above that of maple seedlings following fire or heat stress (Curtis 1959, Grimm 1984, Hengst and Dawson 1994, Huddle and Pallardy 1996).  In another study, Waldrop and Lloyd (1991) reported that oak mortality rates after 26 years of biennial summer burning in mature pine stands in the Coastal Plain were still below 50%, whereas mortality rates of other woody species ranged from about 60 to 80%. This resprouting mechanism is especially critical to the success of northern red oak, as it has thinner bark, and therefore is less resistance to heat damage than other oaks (Crow 1988).

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.  Fire, by removing excessive litter buildup from the forest floor, is important for the successful germination of acorns (Van Lear and Watt 1993).  Not only are areas of thin litter preferred by squirrels and bluejays for acorn burial (Galford and others 1988), but oak seedlings from freshly germinated acorns are more likely to emerge than from areas with heavy litter cover.  But, while removal of thick litter may expedite the germination process, it is important that some humus remain after fires. The humus layer keeps the surface of the soil porous, so that uncached acorns can more easily penetrate the soil, retains moisture, and provides support for the new seedling (Carvell and Tryon 1961).

Fire helps to control insect predators of acorns and new seedlings. Recent studies indicate that prescribed burning may reduce populations of oak insect pests when conducted under proper conditions and at the appropriate time in the insects life cycle (Galford and others 1988). Martin and Mitchell (1981) illustrated how insect populations can be reduced or eliminated directly or indirectly by fire.  Burning may also reduce rodent habitat, eliminating another source of acorn predation (Hannah 1987). A reduction in acorn predators would allow more acorns to be scattered and buried by jays and squirrels, thus enhancing the probability of successful germination.  Evidence suggests that jays collect and disperse only sound nuts (Darley-Hill and Johnson 1981, Deen and Hodges 1990), which implies that if these acorns escape predation they will result in well-established first-year seedlings. 

Effects of Fire Suppression on Oaks

Due to the competitive edge fires give oaks over fire-intolerant hardwoods, oaks are favored by frequent fires in the southern Appalachians, particularly on high-quality sites.  In the absence of fire, oaks often lose this competitive advantage to species that are intolerant of fire but that grow faster in forest openings.  Decades of fire suppression in the southern Appalachians have had several negative effects on oak regeneration. The absence of fire since the turn of the 20th century has allowed species that are intolerant of fire to become established and grow to a size where they—because of thicker bark associated with age—can now resist fire (Van Lear and Watt, 1993). At greater than 5 cm (2 in.) d.b.h., yellow-poplar becomes almost as fire resistant as oaks (Maslen 1989). Mockernut and pignut hickories, scarlet oak, red maple, and blackgum are examples of species that are often found on sites where fire has been long absent (Harmon 1984, Martin 1989).

Suppression of fire has also allowed shrubby understory species to occupy drier sites where fire was once frequent and oak was more dominant. In particular, rhododendron has dramatically increased its extent (Van Lear and Waldrop 1989, Martin 1989). Impenetrable thickets of ericaceous species, such as rhododendron, mountain laurel, and huckleberry, now often dominate midstories and understories of hardwood stands in the southern Appalachians and prevent desirable hardwood regeneration from becoming established (Beck 1989).

Due to the hazards of using fire in steep topography and the susceptibility of these soils to erosion, prescribed fire has 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 public lands. 

Low intensity stand restoration burns have been used in recent years to restore oak-pine forests or pine-dominated stands in the southern Appalachians.  Sometimes there are additional objectives of stand restoration burns, such as stimulating forage production and oak regeneration. There is evidence suggesting that these low-intensity stand 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.  

In 2003, the Great Smoky Mountains National Park executed the largest prescribed burn (1,000 acres) in the park’s history to restore pitch pine, short-leaf pine, and Virginia pine along ridges and slopes.  The low-intensity backing fire was designed to reduce competition and enhance germination for the pines by burning the underbrush and reducing the ground litter.  Another objective of these restoration burns is to benefit wildlife and herbaceous species adapted to frequent fires, such as the Red-cockaded Woodpecker, purple fringeless orchid, mountain catchfly, whiteleaf sunflower, dwarf larkspur, goldenseal, and Indian grass.  Research and monitoring of sites such as this will be invaluable sources of knowledge for land managers hoping to restore oak-pine communities in the Southern Appalachians.

More intense stand-replacement burns have also been used with successful results in oak-pine forests of the Southern Appalachians.   Vose et al. (1999) evaluated the effects of a stand replacement burn used to restore a pine-hardwood forest in the Wine Spring Creek, North Carolina. Nitrogen losses during the stand replacement burn were confined to where fire temperatures were highest on a ridge, but were small enough (i.e. 78 kg N/ha) to be rapidly replenished by atmospheric inputs and N fixation. Moreover, soils and streams showed no response to the burn, and the authors concluded that the effects of the stand replacement burn were limited to the forest floor. Ironically, restoration burns can actually affect soil more when fire intensity is low. For example, Clinton et al. (1998) found that an understory burn in a mixed pine-hardwood stand in Northern Carolina consumed about 40% more humus mass than would have occurred during a stand-replacement burn due to longer residence time of the fire.