EARLY HOLOCENE DEVELOPMENT OF THE GREAT PLAINS GRASSLANDS

Archaeological samples provide a geographically basis for evaluation the rise of the Great Plains grasslands in the central Great Plains. Archeological samples use in this analysis include: Lake Ilo ND, Rustad Quarry ND, Hell Gap WY, Agate Basin WY, Lange-Fergison SD, Ray-Long SD, Jones-Miller CO, Hudson-Meng NB, North Cove, NB among other less well know sites. Non-archeological records, including Wind Cave National Park SD and Brady NB, are used to supplement the archaeological record. Two proxies, carbon isotope analysis and phytolith assemblage analysis, are used to measure change in grassland composition through time and space. Modern samples from native grasslands provide a basis for quantitatively evaluating both grassland composition and controlling climatic variables.

Analyses indicate that populations of C4 grasses were widely established across the region by 10.5 ka BP. Phytolith assemblage analysis suggest that these C4 grass populations include a mix of both mesic-adapted tall (Panicoid) and xeric-adapted short (Chloridoid) grasses. The occurrence of these C4 grasses at such high latitudes early in the Holocene suggest that depressed atmospheric CO2 levels during the last glacial period may have permitted C4 grasses to extend beyond climatic limitations recognized today. Differentiation of the grasslands into the tall-grass prairies of the more mesic east side of the region and short-grass prairies of the xeric western side of the region did not arise until after 8 ka BP.