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4 Fire Regimes of Southern Forests

The climate of the South is characterized by long, hot growing seasons, abundant rain punctuated by occasional multiyear droughts, and the most frequent wind (Cry 1965) and lightning (Komarek 1964) storms in North America (Muller and Grimes 1998). Lightning becomes increasingly common as one moves from north to south. Natural disturbances such as microbursts, tornadoes, and hurricanes can have major impacts on forest structure (Peterson 2000) and the distribution of fuels, and set the stage for intense fires (Myers and Van Lear 1997).

Before Native Americans arrived, fire occurred mainly in the spring and summer thunderstorm season, ignited by lightning (Martin and Sapsis 1992). Most fires were probably limited in extent, as normally humid and still nighttime conditions in the summer tend to extinguish fires in light fuels. Some fires, however, were undoubtedly far ranging because they were associated with dry weather fronts (Wade and others 2000). Native Americans burned many sites frequently, limiting fuel buildup. They also extended the burning season, setting fires throughout the year, and often several times each year. Periodic high-intensity wind-driven fires or severe-drought fires together with chronic lightning and Native American fires created the open woodlands, numerous smoke columns, and extensive smoke and haze referred to by early European explorers (Landers and others 1990, Olson 1996, Barden 1997).

In explaining the climate and vegetation interactions that influence fire regimes in southern forests, we refer to four broad physiographic regions (Martin and Boyce 1993): the Coastal Plain (Atlantic and Gulf coasts, including peninsular Florida and the Lower Mississippi Alluvial Valley); the Piedmont; the Southern Appalachians (including Appalachian plateaus and mountain ranges); and the Interior Highlands (including the Interior Low Plateaus of Kentucky and Tennessee and the Ozark-Ouachita Highlands). Occurrences and frequencies of fire regimes before European settlement for specific plant communities are shown in Table 1.

Fire-adapted plant communities span the full elevational gradient from saltwater marshes to mountain balds (Wade and others 2000). The extent of these communities at the time of European colonization is difficult to reconstruct because much of this region was cleared and plowed at least once, or logged to support the industrial revolution. An estimated 80 percent of the Coastal Plain was cleared, with some counties reaching near 100 percent (Nelson 1957, Brender 1974). Hamel and Buckner (1998) described the "original southern forest" at three time periods: (1) late glacial times, following retreat of the Laurentide Ice Sheet, but after aboriginal immigration; (2) prior to European contact in 1492; and (3) after the first permanent English settlement in 1607. They concluded that no specific time period represents the "true" original condition of the southern forest because it has been responding to climate change and has been shaped by humans for millennia. Even communities that escaped logging or clearing in the last 200 years have undergone dramatic changes because of decades of fire exclusion.

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