Late Quaternary vegetation history of Rough Canyon, south-central New Mexico, USA

South-central New Mexico, USA, at the junction of the Rocky Mountains, High Plains and Chihuahuan Desert, is one of the better known regions in the la te Quaternary of North America. Plant macrofossils and pollen from a packra t midden series in Rough Canyon, New Mexico allows refinement of plant dist ributions and paleoclimates in this transitional area since full glacial ti mes. From 17000 to 12000 C-14 yr BP, Pinus edulis-Juniperus scopulorum wood lands dominated limestone substrates between 1800 and 1490 m. with Pseudots uga menziesii and other mixed-conifer species restricted to shady, north-fa cing slopes. Juniperus deppeana, the dominant juniper today above 2000 m in southern New Mexico, is conspicuously absent from glacial middens and must have been displaced south of the US-Mexico border. The minimum climatic co nditions for P. edulis-J. scopulorum woodlands are ca 20% wetter and 3.5-5 degreesC cooler (July mean maximum temperatures) than the modern climate at Rough Canyon. Holocene warming/drying may have started as early as 12 000 C-14 yr BP with the extirpation of J. scopulorum from Rough Canyon, and was completed by at least 10 540 C-14 yr BP. The record for arrivals of some d esert species is confounded by traces of pollen and macrofossils in some of the glacial middens, which could signify either earliest occurrence or tem poral mixing (contamination) of assemblages. AMS C-14 dating can discrimina te between early arrival and contamination in midden macrofossils but not i n pollen. AMS dates show that Choisya dumosa, presently near its northern ( cold) limits at Rough Canyon, endured late glacial winters, possibly as clo nal populations. Some Larrea tridentata leaves and pollen occur in middens dominated by conifers and oaks no longer at the site; an AMS date of 3205 C -14 yr BP on Larrea leaves from one midden indicates contamination. Evidenc e for some macrofossil contamination, however, does not rule out the possib ility that pollen of desert elements (e.g. Larrea, Prosopis) in late glacia l-early Holocene middens indicates their presence in the Tularosa Basin, we ll ahead of their local appearance in Rough Canyon. Finally, the increasing dominance of desert elements after 5000 C-14 yr BP in the Rough Canyon ser ies and elsewhere in the northern Chihuahuan Desert could reflect slow, pos tglacial migration from the south and/or progressive encroachment with grad ual stripping of soils formed during the last glacial period. (C) 2001 Else vier Science B.V. All rights reserved.