The notion a squirrel could have traveled through treetops from the Atlantic Coast to the Mississippi River when Europeans first discovered North America is a myth. Extensive grasslands existed throughout eastern North America then. Many factors contributed to their origin. Indians annually set fire to the woods to improve habitat for the deer, bear, and turkeys they ate. Normally, this created an open woodland environment because many species of trees can survive light grass fires. But in some areas, fires can consume much of the tree cover, creating open grassland. Indians also removed trees when they planted corn fields. Abandoned corn fields became prairie-like for at least 10 years before reverting to forest. Natural lightning ignited fires, tornados, and hurricanes also destroyed forests, creating pockets of prairie within eastern forests. In some locations soil conditions that favor grass over trees resulted in grasslands predominating instead of trees.
Hempstead Prairie on Long Island, New York is an example of a prairie pocket within the eastern forest. It originally was 50 square miles in extent and hosted grassland species of birds such as upland sandpiper, prairie chickens, and eastern meadowlark. This was tall grass prairie with 5-foot-tall grasses and a great variety of flowering plants. It was still mostly intact until about 1969, but suburban development during the 1970s destroyed most of it. Today, just 19 protected acres remain. Homeowners are encouraged to plant native species of plants in their yards, but it will never be the same.
Every region in mostly forested eastern North America had pockets of prairies within the wooded landscape. Below is a map made by surveyors of an area in Arkansas during the early 1800s. Most of the landscape at this time consisted of oak and pine forest and bottomland swampy forests, but there were 5 major prairies and 9 smaller ones in this area. The larger prairies were even given names. Most of eastern North America was forest like this pock-marked with prairies.
2 species of birds require extensive stretches of grasslands with no trees–upland sandpipers (Bartamia longicauda) and prairie chickens (Tympanuchus cupido). These birds were formerly abundant in eastern North America. Now, upland sandpipers are rare in the east and prairie chickens have been extirpated in the region. I hypothesize some populations of eastern prairie chickens, most notably the heath hen, were unique species. Because these species are so habitat-specific, they can be used as index species in the subfossil record for the presence of grasslands. The remains of both species, dating to the late Pleistocene, have been found in Kingston Saltpeter Cave and Yarbrough Cave in Georgia, and Bell Cave in Alabama. Most of the bird species remains found at these fossil sites are woodland, wetland, or generalist species, but the presence of upland sandpiper and prairie chicken remains is evidence there were pockets of prairies in north Georgia and north Alabama about 13,000 years ago.
References:
Bragg, Don. C.
“Natural Pre-settlement Features of the Ashley County, Arkansas Area”
American Midland Naturalist 2003
Marinelli, Janet
“Amid the Sprawl, A Long Island Prairie Makes a Quiet Comeback”
Yale Environmental 360 December 2022
GeorgiaBeforePeople 
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