Forest and Tundra Zones of the Upper Gunnison Basin

Author - Steve Emslie; Dept. of Biological Sciences, Univ. of North Carolina

This map of the Upper Gunnison Basin illustrates major forest communities based on the dominant conifer species. Needles and seeds of these species also have been identified from fossil localities throughout the Basin. These localities are indicated on the map and include two cave deposits (Cement Creek and Haystack Caves) that have produced late Pleistocene and Holocene fossils of plants and vertebrates. Dr. Steve Emslie and his students at the University of North Carolina, Wilmington, currently are completing analyses of these remains.

Other localities on the map indicate where ancient packrat middens have been collected from small caves and crevices. These middens have produced plant remains that indicate shifts in major vegetation communities during the late Holocene. For example, middens from Red Creek and the West Site each have produced needles of Lodgepole pine (Pinus contorta) though both sites occur in largely sagebrush (Artemisia spp.) shrubland with scattered juniper (Juniperus utahensis) and Douglas fir (Pseudotsuga menziesii). Radiocarbon dates on these needles provided ages of 3320⁺_-60 and 3180⁺_-40 years before present (B. P.).  The nearest stand of Lodgepole pine is approximately 15 km to the north of these sites as shown by the green color on the map. Thus, the midden data reveal that Lodgepole pine forest was more extensive at lower elevations in the Upper Gunnison Basin over 3000 years ago. This pine is a fire-adapted species and, while it occurs at all elevations up to 3658 m in the western U. S., it does not grow lower than about 2300 m in Colorado. These data suggest that the climate was cooler, and perhaps drier, in the Upper Gunnison Basin compared to the present.

Other midden data indicate that plant communities were similar to the present from 3000 to 1500 B. P. No plant species have been identified from middens of these ages that are not found in the same area today where the midden is located. Two other middens at Rocky Brook and East Indian Creek, however, indicate other climatic events. These middens have produced remains of another subalpine conifer, Bristlecone pine (Pinus aristata), that occurs only at higher elevations near these sites today. These species, dated at 560 and 240 B. P., appear to have moved to lower elevations and again suggest that cooler and drier conditions may have prevailed at those times compared to today.

Additional data are needed to improve the resolution of these climatic events and are being gathered in an on-going study of the Upper Gunnison Basin ecology and paleoecology at the University of North Carolina, Wilmington.

Vegetation zones were determined by Jerry Chonka, USFS, Gunnison; the map was digitized by Matthew Martin.

May 1999

Please visit: Late Holocene Environmental Change in the Upper Gunnison Basin, Colorado