Inferences about winter temperatures and summer rains from the late Quaternary record of C4 perennial grasses and C3 desert shrubs in the northern Chihuahuan Desert

Late Quaternary histories of two North American desert biomes-C-4 grasslands and C-3 shrublands-are poorly known despite their sensitivity and potential value in reconstructing summer rains and winter temperatures. Plant macrofossil assemblages from packrat midden series in the northern Chihuahuan Desert show that C-4 grasses and annuals typical of desert grassland persisted near their present northern limits throughout the last glacial-interglacial cycle. By contrast, key C-3 desert shrubs appeared somewhat abruptly after 5000 cal. yr BP. Bioclimatic envelopes for select C-4 and C-3 species are mapped to interpret the glacial-interglacial persistence of desert grassland and the mid-to-late Holocene expansion of desert shrublands. The envelopes suggest relatively warm Pleistocene temperatures with moist summers allowed for persistence of C-4 grasses, whereas winters were probably too cold (or too wet) for C-3 desert shrubs. Contrary to climate model results, core processes associated with the North American Monsoon and moisture transport to the northern Chihuahuan Desert remained intact throughout the last glacial-interglacial cycle. Mid-latitude effects, however, truncated midsummer (July-August) moisture transport north of 35 degrees N. The sudden expansion of desert shrublands after 5000 cal. yr BP may be a threshold response to warmer winters associated with increasing boreal winter insolation, and enhanced El Nino-Southern Oscillation variability. Published in 2006 by John Wiley & Sons, Ltd.