Full-Glacial and Recent Vegetation of Livingston Hills, Presidio County, Texas

Abstract

A fossil packrat midden from 1280 m elevation in the limestone Livingston Hills south of Shafter, Presidio County, Texas, was radiocarbon dated at 15,695 ? 230 B. P. (A-1581 on Juniperus). The paleocommunity was a pinyonjuniper woodland with Pinus edulis and 26 associated species. Holacantha stewarti was an important desert species in the paleocommunity. A total of 139 species was recorded in the present xeric Chihuahuan Desert flora near the midden site. Late Pleistocene paleocommunities and the timing of biotic changes in the northern Chihuahuan Desert are discussed. The Chihuahuan Desert reaches its lowest elevations along the United States-Mexico International Boundary along the Rio Grande in the Big Bend of Texas. The varied geology and vegetation of the region produce as scenic a painted desert landscape as any in the southwestern deserts. However, the desert has not been in the Big Bend for long. Wells' (1966) analysis of fossil packrat (genus Neotoma) middens from the Big Bend found a xeric woodland with pinyon (Pinus cembroides var. remota) as low as 600 m elevation in Maravillas Canyon during the last glaciopluvial period. His sites were from 600 to 1200 m elevations in three areas peripheral to the Chisos Mountains. Wells (1977) suggested that the present Chihuahuan Desert vegetation entered the Big Bend less than 11,500 years ago. Here we report a late Pleistocene plant macrofossil assemblage from an ancient packrat midden from the west side of the Big Bend in the Livingston Hills (Fig. 1).