Elevational Range

C. Hart Merriam's Life Zones. Drawing by D.M. Zahnie

On the semi-arid Colorado Plateau elevation is an important factor in determining what assemblages of species or biotic communities occur in a given location. As one moves upward in elevation temperatures generally decrease and precipitation increases.

C. Hart Merriam's studies of the biota from the top of the San Francisco Peaks at 12,600 feet to the bottom of Grand Canyon at less than 3000 feet impressed upon the scientific community the importance of elevation and latitude on the location of biotic communities. Subsequent studies have revealed that elevation is only one of a complex of factors that determine the presence or absence of species, populations, and communities. These factors include aspect (i.e., which direction the slope is facing), wildfire history and frequency, and soil type.

Evidence from paleoecological studies suggest that elevational ranges for particular species have fluctuated over time in response to major climatic changes. For example, today on the San Francisco Peaks, subalpine forests of Engelmann spruce generally grow from 9500 to about 11,500 feet (see figure above). At the height of the last glaciation (about 20,000 years ago) this species grew as low as 7000 feet, and probably not much higher than 9000 feet, far lower in than its current distribution. Timberline in the region, which today is about 12,000 feet, was apparently much higher during much of the middle Holocene (7500-3000 years ago) and a bit lower than today about 1500 years ago (see figure below). These significant fluctuations are a result of species responding to the dynamic nature of the earth's climate over time.

Source: Robert S. Thompson and Katherine H. Anderson "Past Climate and Vegetation Changes in the Southwestern United States"  http://geochange.er.usgs.gov/sw/impacts/biology/pastclim/

Packrat Midden Research in the Grand Canyon. On the Colorado Plateau the ice age (Pleistocene) vegetation of the Grand Canyon has been determined through the analysis of plant fossils preserved in caves and fossil packrat middens.  Large changes occurred as the most recent ice age ended and the Holocene era began. Adapted by Kenneth L. Cole from his journal article.

Paleobotany and Paleoclimate of the Southern Colorado Plateau. The biota of the Colorado Plateau during the middle (50,000-27,500 B.P.) and late (27,500-14,000 B.P.) Wisconsin time periods was dramatically different from that seen today. Differences were primarily a result of major climate changes associated with the last major glacial period. This site examines the environment of the southern plateau during this time. Adapted by R. Scott Anderson from his journal article.

Late Holocene Environmental Change in the Upper Gunnison Basin, Colorado. The Upper Gunnison Basin is a high elevation (3100 to 3600 m) region on the edge of the Colorado Plateau in southwestern Colorado. Its unusual ecological characteristics include an absence of plant and animal taxa that should occur here. Fossil and archaeological evidence indicates that many of the missing species existed in the Basin during the late Pleistocene to middle Holocene. Authored by Steve Emslie.

Anderson, R. S., Betancourt, J. L., Mead, J. I., Hevly, R. H. and Adam, D. P. 1999. Middle- and Late Wisconsin paleobotanic and paleoclimatic records from the southern Colorado Plateau, USA. Palaeogeography, Palaeoclimatology, Palaeoecology 154 (1/2).

Betancourt, J. L. 1990. Late Quaternary biogeography of the Colorado Plateau. Pp. 259-293 In: Betancourt, J. L., Devender, T. R. V. and Martin, P. S., editors. Packrat Middens: The Last 40,000 years of Biotic Change. University of Arizona Press, Tucson.

Cole, K. L. 1990. Late Quaternary vegetation gradients through the Grand Canyon. Pp. 240-258 In: Betancourt, J. L., Martin, P. S. and Devender, T. R. V., editors. Packrat Middens: the last 40,000 years of biotic change. University of Arizona Press, Tucson.

Cole, K. L. 1990. Reconstruction of past desert vegetation along the Colorado River using packrat middens. Palaeogeography, Palaeoclimatology, and Palaeoecology 76: 349-366.

Dye, A. J. and Moir, W. 1977. Spruce-fir at its southern distribution in the Rocky Mountains, New Mexico. American Midland Naturalist 97: 133-146.

Sharp, S. E. 1991. Late-Pleistocene and Holocene vegetation change in Arches National Park, Grand County, Utah and Dinosaur National Monument, Moffat County, Colorado. M.S. Thesis. Northern Arizona University, Flagstaff, AZ, 95 pp.

Stein, S. J. 1988. Explanations of the imbalanced age structure and scattered distribution of ponderosa pine within a high-elevation mixed coniferous forest. Forest Ecology and Management 25: 139-153.

Withers, K. and Mead, J. I. 1993. Late Quaternary vegetation and climate in the Escalante River basin on the central Colorado Plateau. Great Basin Naturalist 53: 145-161.