Vegetation and environment in Eastern North America during the Last Glacial Maximum

Knowledge of the vegetation and environment of eastern North America during the Last Glacial Maximum (LGM) is important to understanding postglacial v egetational and biogeographic dynamics, assessing climate sensitivity, and constraining and evaluating earth-system models. Our understanding of LGM c onditions in the region has been hampered by low site density, problems of data quality (particularly dating), and the possibility that LGM vegetation and climate lacked modern analogs. In order to generate improved reconstru ctions of LGM vegetation and environment, we assembled pollen and plant mac rofossil data from 21 and 17 well-dated LGM sites, respectively. All sites have assemblages within the LGM timespan of 21,000 +/- 1500 calendar yr BP. Based on these data, we prepared maps of isopolls, macrofossil presence/ab sence, pollen-analogs, biomes, inferred mean January and July temperatures and mean annual precipitation for the LGM. Tundra and open Picea-dominated forest grew along the Laurentide ice sheet, with tundra predominantly in th e west. In the east, Pinus-dominated vegetation (mainly P. banksiana with l ocal P. resinosa and P. strobus) occurred extensively to 34 degrees N and p ossibly as far south as 30 degrees N. Picea glauca and a now-extinct specie s, P. critchfieldii, occurred locally. Picea-dominated forest grew in the c ontinental interior, with temperate hardwoods (Quercus, Carya, Juglans, Lir iodendron, Fagus, Ulmus) growing locally near the Lower Mississippi Valley at least as far north as 35 degrees N. Picea critchfieldii was the dominant species in this region. The Florida peninsula was occupied by open vegetat ion with warm-temperate species of Pinus. Eastern Texas was occupied by ope n vegetation with at least local Quercus and Picea. Extensive areas of peni nsular Florida and the continental interior had vegetation unmatched by any modern pollen samples. The paleovegetational data indicate more extensive cooling in eastern North America at the LGM than simulated by either the NC AR CCM0 or CCM1 climate models. The occurrence of cool-temperate conifers a nd hardwoods as far north as 34-35 degrees N, however, indicates less sever e cooling than some previous reconstructions. Paleoclimate inferences for t he LGM are complicated by lowered atmospheric CO, concentrations, which may be responsible for the open nature and dominance of conifers in LGM vegeta tion. (C) 2000 Elsevier Science Ltd. All rights reserved.