Eastern savannas of the United States

The eastern savannas of the United States covered large portions of the east side of the continent until the early 20th century. These were in a fire ecology of open grassland and forests with low ground cover of herbs and grasses.

The frequent fires which maintained the savannas were started by the region's many thunderstorms and Native Americans, with most fires burning the forest understory and not affecting the mature trees above. Before the arrival of humans about 15,000 years ago, lightning would have been the major source of ignition, the region having the most frequent wind and lightning storms in North America. The European settlers who displaced the natives blended the local use of fire with their customary use of fire as pastoral herdsmen in the British Isles, Spain, and France.

In the southern pine savanna, each area burned about every 1–4 years; after settlers arrived burning happened about every 1–3 years. In oak–hickory areas, estimates range from 3 to 14 years, although trails were kept open with fire.

Of all the United States, southeastern flora has been least changed in composition during the last 20,000 years. During the Last Glacial Maximum about 18,000 years ago, when the glacial front extended south to the approximate location of the Ohio River, preexisting natural communities in the Southeast remained largely intact. As a result, the Southeast contains a high level of endemism and genetic diversity as would be expected of an old flora.Temperate deciduous forests dominated from about 33° to 30° N. latitude, including most of the glacial Gulf Coast from about 84° W. longitude. The coastline later changed during glacial melt, both in the Mississippi River valley and sea level rise of 130 meters (430 ft). Regional climate was similar to or slightly drier than modern conditions. Oak, hickory, chestnut, and southern pine species were abundant. Walnuts, beech, sweetgum, alder, birch, tulip tree, elms, hornbeams, tilias, and others that are generally common in modern southern deciduous forests were also common then. Grasses, sedges, and sunflowers were also common. Extensive mesophytic forest communities, similar to modern lowland and bottomland forests, occurred along major river drainages, especially the Mississippi embayment, the Alabama-Coosa-Tallapoosa Basin, the Apalachicola-Chattahoochee-Flint Basin, and the Savannah River Basin.

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