PACKRAT MIDDENS AND LATE HOLOCENE ENVIRONMENTAL CHANGE IN SOUTHWESTERN COLORADO

Abstract

Seventeen middens of the bushy-tailed packrat (Neotoma cinerea), ranging in age from 3450 ± 40 to 160 ± 50 radiocarbon years before present (B.P.), were collected in 1996 from the Upper Gunnison Basin, Colorado. Eight of these subfossil middens contained plant remains from species that no longer occur near the locations of the middens. Radiocarbon dates on conifer remains indicated shifts in forest communities in the late Holocene at 3320, 560, and 240 B.P. Past climates were cooler than today at 3320 B.P., when mixed lodgepole (Pinus contorta) and ponderosa pine (P. ponderosa) forest expanded to lower elevations in the basin. Conditions became warmer between 1500 to 950 B.P., with additional cooling from 660 to 170 B.P., corresponding with cooling periods in the 1300s and during the Little Ice Age (500–150 B.P. or 1500–1850 CE). These data indicated that the late Holocene of Colorado was marked by episodes of climate change that previously have not been identified in the paleoclimatic record.