XVI International Botanical Congess

A 25-km grid of modern climatic data for North America was compared with the geographic ranges of important plant species to explore the relations between climate and plant distributions. Jaccards coefficient was used to determine which gridpoints had modern vegetation similar to that in macrofossil assemblages preserved in Pleistocene packrat middens from southern Nevada. Paleoclimatic reconstructions based on this method (for ~1500 m elevation) indicate that temperatures were ~8° C colder than today at the last glacial maximum (~18,000 yr B.P.). Mean annual precipitation was as much as 3 times modern values at that time. However, this may be a minimum estimate, as plants would have required more precipitation than today under the lower-than-modern levels of atmospheric carbon dioxide.