Presettlement vegetation of part of northwestern Moffat County, Colorado, described from remnants

—A general botanical inventory of a part of northwestern Moffat County, Colorado, resulted in the location of"remnants" ofthe presettlement vegetation spectrum that are largely unaltered by grazing, logging, or other recent human-related land uses. The 69 samples taken from these remnants were classified into 22 plant associations. Composition, structure, environmental location, geographical range, and response to disturbance are discussed for each association, and a photograph of each is presented. Seven of the 22 associations are apparently restricted to the study area. Restricted associations occur in the more extreme environments of the study area, such as on calcareous substrata or very xeric sites. More niesic sites along ephemeral creeks, on north-facing slopes, or on sandstones support plant associations that have much wider ranges, many ofthem extending across the northern Great Basin. The vegetation that occupied the landscape in the western United States prior to settlement has been effectively extirpated in some areas by conversion to cultivation or by urban development. In most ofthe remainder, other kinds of land use have resulted in alteration of the presettlement composition and structure. The most pervasive and most consequential of these other land uses are domestic livestock grazing and logging, though mining and recreation have had substantial effects in more localized areas. Also pervasive has been the replacement of nati^'e plant species by exotics. Additional effects have resulted from fire control, loss or modification of native herbivore populations, exotic diseases, air polluition, and acid precipitation. In some parts of the western United States, and in many parts of the eastern United States, the composition and structure of the presettlement vegetation can only be known now by reference to historical accounts, early photographs, and other secondary records. Vale (1982) reviewed methods of analyzing these sources. Nevertheless, in parts of the West it is still possible to locate remnants of the presettlement vegeitation, which have essentially escaped alteration, though such remnants are exceedingly rare at lower elevations or on very productive >ites and' are disappearing as land uses continue or accelerate. These remnants have been widely used in :he forested parts of the western United States to develop "habitat type" classifications (Pfister 1982). Such classifications are irreplaceable records of the detailed composition and structure of the presettlement vegetation. Some of these remnants, occurring on federal lands, have been protected from further alteration or loss by designation as Research Natural Areas under regulations and policies of the U.S. Department of the Interior, Department of Agriculture, and other departments. Perpetuation of remnants in such designated Research Natural Areas means that they will be available in the future for more extensive study. Very few opportunities are available for the study of ecosystem function on unaltered sites. Without such studies it is difficult for land managers to know how to most efficiently manage land uses on similar lands for maximum benefit with minimum alteration. Such protected remnants also serve an important role in the long-term perpetuation of their component plants and animals. The natural vegetation of some parts ofColorado is nearly unknown (Baker 1982a), particularly at lower elevations. An earlier report characterized some of the presettlement vegetation of the Piceance Basin occurring on Green River and Uinta formations (Baker 1983). This report extends that earlier report to include additional areas of Green River Formation (Fm.) and other geologic substrata occurring in a part of northwestern Moffat Rocky Mountain Heritage Task Force, 1370 Pennsylvania, Suite 190, Denver, Colorado 80203. ^Department of Biology, Western State College, Gunnison, Colorado 81230.