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The temperatures of the Hypsithermal peaked between 7,500 to 5,000 years BP and were higher than modern temperatures (fig. 24.13). Warming was experienced worldwide, and the Southeastern United States was no exception. Prairies expanded east of the Mississippi River and grasses increased in abundance, aided by native burning. In pollen samples from Missouri at 7,000 years BP, 85 percent of the species represented were grasses. This proportion of grass species is higher than those recorded for modern prairies (Culberson 1993). Accompanying the expanding prairies east of the Mississippi River were pronghorns and badgers. It is conceivable that the modern bison arrived as well (Culberson 1993, Guilday 1982), while the peccary disappeared from the Southeast (Goodyear and others 1979).
Changing vegetation and rapid deglaciation characterized the hypsithermal. Tree species were migrating from Ice Age refuges. More charcoal is mixed with pollen data due to increased burning by humans. Pines and oaks increase on the southeastern landscape (Delcourt and Delcourt 1985, Watts 1980). Only extensive openings and frequent disturbance from natural and native activities (burning, clearing stream bottoms, and gathering firewood) could explain the increase in pines.
During the hypsithermal, study sites in the Shenandoah, Potomac, and Savannah River Valleys indicated subdued flooding intervals. The data would indicate that the dry conditions were occasionally interrupted by wet intervals, which caused increased sedimentation at some locations. Evidence from some places in the Southeast would indicate oscillating periods of precipitation and temperature during periods of the hypsithermal. However, there is no indication of the season in which the precipitation fell. It is clear that the climate was generally drier and hotter during this period and that overall precipitation was low (Blanton and Sassaman 1989). Pollen data indicate that extraordinary vegetation changes occurred over large areas of the Southeast. Compounding the hotter, drier climate was the still lowered water table and lower sea levels as a result of incomplete thawing of the glaciers (Watts 1971).
The Middle Archaic Period differs from the Early Archaic Period due to the continued climatic warming as the hypsithermal progressed. The Morrow Mountain and Guilford cultures were present during the Middle Archaic Period. Archaeological sites indicate a proliferation of Morrow Mountain spear points during this time (Walthall 1980). Food may have been less predictable, elevating competition for resources. Artifacts from these cultures were more crudely made; and settlement sites were small and scattered, possibly due to more frequent relocation resulting from resource scarcity or lack of predictability. However, in the face of severe climatic changes, native populations increased and territories became more defined.
Archaeologists have uncovered evidence of increased external and internal conflict at Kentucky Knoll in Kentucky, the Eva site in Tennessee, and several sites in Alabama. Most conflicts centered around riverine shell-gathering and fishing sites (Walthall 1980). Human activities in coastal areas of the Southeast are poorly documented during this time, possibly due to unstable coastal ecosystems and rising oceans. Subsistence activities appear to be the same as in earlier archaic people. Scattered and scarce resources and increased human populations may have increased conflict between groups.
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