David J Cooper

Colorado State University

South Park is one of the four large intermountain basins that characterize the Rocky Mountains of Colorado (figure 3.1). The basins, typically called "parks," have relatively level to rolling floors and are surrounded by mountain ranges with peaks reaching over 4000 m elevation. The floors of all parks have arid climates with cool summers and very cold winters.

Three characteristics of South Park distinguish it from Colorado's three other major intermountain basins, North Park, Middle Park, and the San Luis Valley:

1. The floor of South Park is much higher in elevation than that of any other intermountain basin in Colorado or in North America.

2. The vegetation on the park floor is a grass-dominated steppe, whereas the other parks are dominated by shrubs.

3. Localized saline groundwater has created saline springs, ponds, and soils in an otherwise nonsaline landscape.

The high elevation of South Park and its surrounding mountains have created persistent habitat and connections for floristic exchange with other high mountain regions in the Northern Hemisphere. Although Colorado has many high mountain ranges, South Park and its surrounding mountains support the highest concentration of plant species that have their main distributions in central Asia (Weber and Wittmann, 2001) and boreal regions of the Holarctic (Hulten, 1968). Although some of the extraordinary plant populations occur in mountaintop alpine tundra environments, most occur on the floor of South Park in steppe, peatland, and salt flat ecosystems.

South Park features large regional variation in elevation and an assortment of bedrock types. Landforms created by geologically recent glaciers and rivers are superimposed on geologically long-lived ridges and bedrock outcrops. The combination of all these factors has created habitat for a wide diversity of species and communities. Well-developed alpine tundra occurs on the highest mountains, and numerous forest types dominated by evergreen and deciduous trees occur on mountain slopes. Mountain-front hills and hogbacks (long ridges formed by tilted resistant rock strata) in South Park support forest and grassland communities that typically are found only much farther south in North America. The grassdominated steppe shares many species with the northern and western Great Plains, the steppes of central Asia, and the mountains of Chihuahua, Mexico. South Park also contains some of the largest expanses of montane wetlands in the western United States, particularly where groundwater flowing through the glacial outwash of the Mosquito Range mountain front discharges onto the floor of the park. This great ecological variability and geographic position suggest that South Park has acted as a crossroads for many floristic elements and has probably provided important biotic refugia for tens of thousands, if not millions, of years.

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