Changes in the Biota of the Colorado Plateau

Green River, Utah. Riparian areas have seen tremendous change over the last 100 years. Photograph courtesy of Cline Library Special Collections, Northern Arizona University.

Changes in the biota can be either natural or human-caused. Species expand and contract their ranges as a natural response to both natural climate cycles and human land use. Disturbances such as floods and fires, whatever their origins, are followed by an orderly process of recolonization known as ecological succession.

The arrival of humans on the landscape about 12,000 years ago began the era of land use as a cause of biotic change. Although the early hunters were probably not entirely to blame, the extinctions of the Colorado Plateau's megafauna were complete within 2,000 years of their arrival.

More recent changes caused either directly or indirectly by human activities on the Plateau include the extirpations of some native species, including the California condor, a number of endemic fish species, and even mammals such as the grizzly bear and the gray wolf. While the list of threatened and endangered species grows, so does the number of non-native and invasive species, especially plants such as tamarisk and Russian olive. The near extirpation of the Colorado Plateau's beaver population by early trappers began the degradation and loss of riparian areas which has become particularly serious in the last few decades. In the last 150 years, grazing, logging and fire suppression policies began to create changes in forest composition and structure which have led to the current high incidence of catastrophic wildfires. Research into the fire ecology of ponderosa pine forests has revealed that frequent low-intensity ground fires were essential to forest health.

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.

Native Americans and the Environment. A comprehensive survey of twentieth century environmental issues facing Native Americans on the Colorado Plateau and throughout the Southwest, including discussions of agriculture, logging, mining, grazing, water rights, and tourism. Adapted from a published journal article by David Rich Lewis.

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.

Fire-Southern Oscillation Relations in the Southwestern United States. A close linkage between fire and climate could diminish the importance of local processes in the long-term dynamics of fire-prone ecosystems. The structure and diversity of communities regulated by fire may have nonequilibrial properties associated with variations in global climate. Successful prediction of vegetation change hinges on a better understanding of climatically driven disturbance regimes and the relative contributions of regional versus local processes to community dynamics. Adapted from a journal article by Thomas W. Swetnam and Julio L. Betancourt.

Changed Southwestern Forests: Resource effects and management remedies. Over 150 years of occupancy by northern Europeans has markedly changed vegetative conditions in the Southwest. Less fire due to grazing and fire suppression triggered a shift to forests with very high tree densities, which in turn contributed to destructive forest fires. Options to deal with these changes include prescribed fire, thinning and timber harvest to mimic natural disturbances and conditions. However, there are barriers to implementing these activities on a scale large enough to have a significant benefit. Adapted from a published journal article by Marlin Johnson.

Where have all the grasslands gone? Numerous ecological studies across the Southwest have documented the decline in herbaceous vegetation (grasses and non-woody flowering plants) while forests thicken and brush invades. Documenting the changes in the Jemez Mountains of northern New Mexico, ecologist Craig Allen considers the evidence that these patterns are tied to changes in land use history, primarily livestock grazing and fire suppression.