The Uncompahgre Plateau Landscape (UPL) occupies 659,246 ha in southwest Colorado (Figure-study area map). The project area is bounded by Highway 62 on the south, the Gunnison and Uncompahgre Rivers on the east, Highway 141 on the north, and Highways 141 and 145 on the west. The Uncompahgre Plateau is one of the major geologic uplift formations in the region. Elevation ranges from 1,350 m in the valley bottoms to approximately 3,200 m at the top of Horsefly peak. The summit is relatively flat with an average elevation of 2,880 m that runs southeast to northwest. The summit drops off quickly on the west side and more gradually slopes downward on the east side. The Plateau is incised by many deep canyons separated by relatively flat mesas that generally run perpendicular to the summit. Large canyons such as Big Red, Tabeguache, Spring Creek, Roubideau, Escalante, Big Dominquez, and Unaweep expose numerous geologic layers of Precambrian granite, Morrison and Dakota sandstones, and Mancos shale. The Plateau watersheds include four major drainages of the Colorado River (Dolores, Gunnison, San Miguel and Uncompahgre Rivers). The climate varies significantly in relation to elevation and topographic gradients. Temperatures range from an average high of 23 degrees (c) in July to an average low of -18 degrees (c) in January. Precipitation ranges from a mean of more than 152 cm on the highest peaks to less than 51 cm in the lower reaches of the study area, and predominately falls in late summer (July and August) and winter (January through March), although there may be significant local variation (Keen 1996).
Several major vegetation types of ecological and economic significance occur within the project area. Each of these types has a unique ecological setting and history (Romme et al. 1992; Floyd-Hanna et al. 1996; Jamieson et al. 1996; Somers and Floyd-Hanna 1996; Spencer and Romme 1996), as well as distinctive human impacts and changes since EuroAmerican settlement. At the lowest elevations, the vegetation is dominated by semi-desert grasslands and savannahs and pinon-juniper woodlands (primarily Pinus edulis and Juniperus osteosperma). At the foothills and on tops of broad plateaus and mesas, the vegetation ranges into Ponderosa Pine (Pinus ponderosa) forest interspersed with shrub-dominated stands (Petran chaparral dominated by Quercus gambelii). The middle slopes are covered by a mosaic of mixed conifers (Pinus ponderosa, Psuedostuga menziesii, Abies concolor, Picea pungens) and quaking aspen stands (Populus tremuloides), broken by occasional meadows and grasslands. The highest elevations contain extensive spruce-fir forests (primarily Picea engelmannii and Abies lasiocarpa), subalpine meadows, and treeless alpine communities on the highest peaks. Running through all these types are riparian woodlands and meadows along the borders of perennial rivers and streams.
Prior to European settlement, landscape dynamics were driven primarily by the patterns of wildfire, which varied dramatically with vegetation type. For example, the median fire interval was only 10-20 years in the low elevation ponderosa pine type; 20-30 years in the dry mixed-conifer type; 50-100 years in the aspen type; and >100 years in the spruce-fir type (Romme et al. 1998). Many individual stands escaped fire for far longer than the median return interval and some burned at shorter intervals, creating a complex vegetation mosaic at the landscape scale. Under this “natural” disturbance regime, stand replacement fires initiated stand development and maintained a coarse-grain mosaic of successional stages and cover types across the landscape, although other disturbance processes, such as landslides, floods, windthrow, insects and disease also played a role on a finer scale. In particular, the disturbance regime of individual stands in the later stages of development is dominated by chronic, fine-scale processes that kill individual trees or small groups of trees (Veblen et al. 1989; Lertzman and Krebs 1991; Veblen et al. 1991a, b; Roovers and Rebertus 1993).
Although limited logging by Euro-American settlers began as early as 1875, the scale and impact of logging increased dramatically in the late 1800's with the advent of railroad logging (Pearson 1950). Most of the activity was confined to the pine forest at lower elevations, such that by 1950, essentially all of the old-growth ponderosa pine forests of this region had been exploited and profoundly altered (Anonymous 1971). In contrast, extensive logging at the higher elevations generally did not begin until much later in the twentieth century. The first large-scale spruce logging operation began in 1946 (US Forest Service, unpublished data). Logging in spruce-fir and mixed-conifer forests was accelerated dramatically in the 1950s and reached a peak in the 1960s and 1970s. Logging was carried out using clearcutting and a variety of partial cutting methods. Clearcutting was discontinued by 1980 in all but aspen forests because of problems in regenerating clearcut stands.
Species composition of most southwestern grasslands, including the meadows and semi-desert grasslands of the UPL, is thought to have been altered substantially by the heavy livestock grazing that occurred in the late 1800s and early 1900s (Fleischner 1994, Belsky and Blumenthal 1997). Heavy, unregulated grazing began in the Uncompahgre region in the 1880s (Rockwell 1999), and continued into the 20th century. Since the the passage of the Taylor Grazing Act in 1934, livestock grazing has been regulated on public lands, and rangeland conditions generally have improved, but we still have legacies of the previously uncontrolled livestock grazing. Grassland composition was not well documented before the onset of grazing, so much of our interpretation is based on inference and informed speculation. A handful of studies documented floristic changes as grazing intensity increased during the early 20th century (Arnold 1950) or compared grazed and ungrazed areas that were otherwise similar (Rummell (1951, Madany and West 1983). These studies show that heavy, sustained cattle and sheep grazing reduced the cover of the more palatable herbaceous species (e.g., Festuca arizonica, Muhlenbergia montana), and even extirpated them from local sites. Invasive non-native species (e.g., Poa pratensis, Taraxicum officinale) and native increaser species (e.g., Wyethia amplexicaulis, Dugaldia hoopesii, Achillea millefolium) have replaced the formerly dominant bunchgrasses in many places (Mullen 1992, Redders 2003a). Thus, many grasslands that today are dominated by grazing-tolerant species may have had a substantially different composition 150 years ago. Although it is difficult to reconstruct pre-1880 species composition in this vegetation type, where nearly every stand has been heavily grazed, it is thought that the perennial grasses (e.g., Stipa comata, Bouteloua gracilis and Hilaria jamesii) were generally dominant in most areas (Heil et al. 1993, Romme et al. 1993).