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Mountains and Interior Highlands Regions

Fire played a major role in shaping vegetation communities in the Appalachian Mountains. Overstories of southern yellow pines (Virginia, shortleaf, pitch, and Table Mountain) typically dominate south- and west-facing slopes (Whittaker 1956), but in the absence of hot fires at rather frequent intervals, hardwoods will succeed pines. Table Mountain pine is well adapted to fire because of its serotinous cones. Although these can open without fire, many remain closed and ensure a supply of seed regardless of the time of year when a fire occurs (Barden 1977). This adaptation allows Table Mountain pine to cast seeds when seeds of other pine species would be destroyed. Serotinous cones have also been observed in pitch pine and rarely in Virginia pine, but this character is not well documented. Shortleaf and pitch pines can sprout from the root collar after topkill by fire. Fires of human origin probably perpetuated pine in the Appalachians since lightning fires did not occur frequently enough or were not intense enough to maintain pines on these xeric sites (Whittaker 1956). Fire protection in recent decades has allowed hardwoods to dominate on sites where pines once thrived.

Oak-hickory forests—The oak-hickory forest type (Barrett 1994, Braun 1950) occurs primarily on average to dry upland sites, but it also can be found on moist upland sites, depending upon past disturbance history. The oak-hickory type historically had an understory fire regime (Brose and others 2001, Van Lear and Waldrop 1989, Wade and others 2000), but presettlement fire frequencies are not known. Conservative estimates from dendrochronological studies suggest fire return intervals of 2.8 years (Cutter and Guyette 1994) to 14 years (Buell and others 1954, Guyette and Dey 1997). The frequency and extent of Native American burning decreased substantially after European contact. As a result, forest canopies closed over previously open grasslands, savannas, and woodlands (Buckner 1983; Denevan 1992; Dobyns 1983; MacCleery 1993, 1995; Pyne 1997). European settlers of oak-hickory forests increased the frequency and extent of burning and shortened fire-return intervals to 2 to 10 years; they burned many sites annually (Cutter and Guyette 1994, Guyette and Dey 1997, Holmes 1911, Sutherland 1997, Sutherland and others 1995).

Presently, infrequent low-intensity surface fires during the spring and fall characterize the fire regime of oak-hickory forests. These fires are caused almost exclusively by humans and burn small areas (Barden and Woods 1974, Pyne and others 1996, Ruffner and Abrams 1998). Fire exclusion created a fuel complex that is probably very difficult to ignite. 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). These shrubs are shade tolerant and evergreen, shading the forest floor throughout the year. Although the forest floor rarely dries enough to support surface fire, the ericaceous shrub layer is flammable. When it burns, it typically supports intense crown fires.

Mixed mesophytic hardwoods—The hardwood forests of the Appalachian and Ozark Mountains and the upland hardwoods of the Coastal Plain and Piedmont have been grazed and burned regularly from the time of earliest settlement (Van Lear and Waldrop 1989). In the absence of fire, a mixed mesophytic forest develops. Although little is known about presettlement fire, it appears that fire was much more common in the mesophytic forests west of the Appalachian divide than in those to the east (Harmon 1984).

Table Mountain pine—Prehistoric fire regimes are unknown, but the presence of serotinous cones suggests that Table Mountain pine is adapted to stand replacement fires (Wade and others 2000). However, some stands are known to regenerate successfully without fire (Barden 1977, Williams and Johnson 1992), and crown fires can create seedbed conditions too xeric for optimum survival (Waldrop and Brose 1999). The historic fire regime for Table Mountain pine stands is probably best described as mixed. Native Americans exposed both Table Mountain pine and pitch pine to frequent understory burns, keeping these stands fairly open. Stand replacement fires probably occurred only when Native Americans were not living in a particular location and fuel loads became heavy. Fires in Table Mountain pine were more frequent, more intense, and probably larger earlier this century (Barden and Woods 1974). Evidence from existing stands supports this mixed fire regime. Table Mountain and pitch pines occur as uneven-aged stands throughout the Southern Appalachians, with most trees ranging from 50 years to over 200 years old (Brose and others 2002, Sutherland and others 1995). Abundant mountain laurel in the same stands is younger than 50 years old, suggesting that frequent low-intensity fires created and maintained these uneven-aged stands until the 1950s. Fire exclusion since the 1950s allowed mountain laurel to establish and create understory conditions that prevented the pines from regenerating.

Pitch and Virginia pines—Mixed severity fires were probably prevalent over much of the range of pitch and Virginia pines. Native American burning maintained pitch pine as an understory fire regime type, with a 2- to 10-year fire interval (Wade and others 2000). This frequency maintained stands with relatively large pines, scattered smaller pines and oaks, and sparse understory besides low ericaceous shrubs and herbs (Little 1946, 1973). The historical fire regime in Virginia pine is unknown but was probably less frequent and resulted in higher mortality. Today, there is a mixed fire regime with long fire-return intervals. The majority of wildfires occur during the growing season when damage is greater.

Southern forest types with long fire-return intervals—Only three vegetation types in southern forests typically have long fire-return intervals: mangroves, high elevation spruce-fir, and northern hardwoods. Surface and ground fires are precluded from mangroves because of their location in tidal zones, but lightning may influence stand dynamics and crown fires can enter after severe freezes that occur every few decades (Wade and others 1980). Spruce-fir forests, which occur from the Southern Appalachians northward, burn only after periodic spruce budworm epidemics, probably on the order of centuries (Wade and others 2000). Northern hardwoods occur only on north-facing slopes and deep coves in the South; return intervals there are on the order of millennia (Lorimer 1977).