VEGETATION CHANGE ON SOUTHERN HIGH PLAINS DURING THE PLEISTOCENE-HOLOCENE TRANSITION

Pollen, phytolith, and carbon isotope records from the Southern High Plains of Texas and New Mexico provide evidence for both abrupt and gradual shifts in climate and vegetation. The inferences are based on a comparison of fossil records from 3 playa fill sequences: San Jon Site, NM, Barnes Playa, TX, and Nall Playa, TX. Data from the Lubbock Lake Site, and scattered other playa localities contribute to the body of evidence.

Full glacial vegetation was characterized by sagebrush and C3-dominated grasslands. Limited pollen evidence for spruce and other trees suggests isolated populations along fire-protected escarpments during the full glacial times. By 12,000 RCYBP grasslands composition began to shift from C3-domination towards mixed C3/C4 grassland. Higher levels of tall-grass (Panicoid) phytoliths, along with greater diatom production, occurred between 11,400 to 10,200 RCYBP. While this period generally represents more mesic conditions, suggestion of abrupt climatic changes throughout this transitional window are also present. Across this Pleistocene-Holocene transition there was a slow, steady rise in shortgrass (Chloridoid) C4 grasses culminates in the rise of the short-grass ecosystem between 8000 and 7500 BP. The record of vegetation change has important implications for bison evolution and Paleoindian adaptation during across the Pleistocene-Holocene transition.