Some species of megafauna that used to live in southeastern North America required large expanses of grasslands. Shady forests inhibited the growth of their favorite foods, though seasonally the grazers would move into the woods for acorns and berries. However, closed canopy forests could not support herds of grazers that depended upon tons of grasses and forbs found only in sunny conditions. The Columbian mammoth, bison, elk, horse, half-ass, and Harlan’s ground sloth were all denizens of open environments. In the coastal plain of the southeast region, open environments were always common no matter the climatic stage. During warm interglacials and interstadials, longleaf pine savannah predominated while deep forested swamps were restricted to river valleys or low areas. And during cold stadials dry prairies with some thickets of scrub oak were the most common environment. But in the piedmont and mountain regions of the south, conditions usually favor trees over grass. Hilly terrain and abundant creeks act as natural firebreaks and without fire forests are likely to become the climax type of environment.. Yet, evidence from the fossil record, and accounts of early colonists prove that grazers lived in these regions as well. I hypothesize megafauna grazers ranging in the piedmont region of the south were mostly found in areas with soils derived from ultramafic rock. The following link is a geological map showing where surpentine barrens and soils derived from ultramafic rock can be found in the piedmont region. I believe these areas supported most of the megafauna herds of grazers formerly found in the piedmont region. http://pubs.usgs.gov/imap/0476/plate-1.pdf
Mixed herd of bison and elk in Land Between the Lakes on the border between Kentucky and Tennessee. Herds like this ranged into the southeastern piedmont region till about 1760, though they may have been absent during times of higher Indian occupation of the land.
Horses can survive in wooded areas but they prefer grassy habitats.
Western Leaf Beetle (Diabratica cristata). It ranges over much of the western Great Plains region of North America, but relic populations of this species exist on serpentine barrens in the eastern area of the continent.
Soils derived from ultramafic rocks have low magnesium/calcium ratios, and they contain heavy concentrations of toxic metals leached from the rock. (See:https://markgelbart.wordpress.com/2013/01/01/a-serpentine-barren-in-georgia-burkes-mountain/) Grass is able to outcompete trees in these types of environments, especially when aided by the occasional fire. They are referred to as barrens. In some areas with lesser degrees of soil toxicity, they may support open woodlands. They aren’t completely treeless, but there is enough space between the trees for grass and forbs to grow. I suspect a barren hilltop where William Bartram, an 18th century naturalist, found the bones of bison, elk, deer, and human was Burke’s Mountain in Columbia County–a well known surpentine barren. The geological map also shows ultramafic derived soils in the bottom third of Elbert County, McDuffie County east of Wrightsboro, the northern part of Wilkes County, Green and Taliaferro Counties, Columbia County along Greenbrier Creek, a big swath of territory in Jasper-Putnam-and Monroe Counties, and in various areas around present day Atlanta. In Alabama ultramafic soils cover much of Coosa, Chilton, Clay, and Cleburne Counties. In South Carolina they are found in Abbeville, McCormick, and Greenwood Counties. Many small areas with ultramafic soils have not been mapped.
Indian populations collapsed after 1600 when the tribes came into contact with DeSoto’s leftover pigs that went feral. Many died when they contracted swine flu or trichinosis. Later, Indian populations continued to decline because of their weak resistance to smallpox, measles, and alcohol–unwelcome gifts bestowed upon them by the British colonists. The decrease in the human population allowed elk and bison, the only American megafaunal grazers to survive the end Pleistocene extinctions, to increase in the piedmont region during early colonial times because they were able to graze on abandoned Indian fields that provided additional habitat besides the natural barrens which were never suitable for cultivation. This explains why early British colonists saw what they mistakenly thought was pristine wilderness. Actually, wilderness was reclaiming land from a civilization in collapse.
Bison lived as far south as north Florida during early Colonial times, probably recolonizing the region for the first time in thousands of years. Mark Catesby reported them foraging in the morning and evening on the grasslands, but they spent the heat of the day in shady canebrakes near creek or river bottoms where they were easy to track in the mud. Elk didn’t range as far south as the coastal plain during Colonial times, but an elk fossil has been found in Charleston, South Carolina. Cool stages of the Pleistocene may have allowed elk to inhabit parts of the coastal plain, but no elk fossils have ever been found in Florida. Elk probably never developed resistance to parasites that abound in frost free environments.
These open environments in the piedmont were also home to prairie chickens, upland sandpipers, common nighthawks, meadowlarks, and other birds that prefer relatively treeless landscapes.