Rocky Mountain Front Range Foothill Grassland

This ecological system typically occurs between 1600 and 2200 m in elevation. It is best characterized as a mixedgrass to tallgrass prairie on mostly moderate to gentle slopes, usually at the base of foothill slopes, e.g., the hogbacks of the Rocky Mountain Front Range where it typically occurs as a relatively narrow elevational band between montane woodlands and shrublands and the shortgrass steppe and mixedgrass prairie, but extends east on the Front Range piedmont alongside the Chalk Bluffs near the Colorado-Wyoming border, out into the Great Plains on the Palmer Divide, and on piedmont slopes below mesas and foothills in northeastern New Mexico. A combination of increased precipitation from orographic rain, temperature, and soils limits this system to the lower elevation zone with approximately 40 cm of precipitation/year. It is maintained by frequent fire and associated with well-drained clay soils. Usually occurrences of this system have multiple plant associations that may be dominated by Andropogon gerardii, Schizachyrium scoparium, Nassella viridula, Pascopyrum smithii, Sporobolus cryptandrus, Bouteloua gracilis, Hesperostipa comata, or Hesperostipa neomexicana. In Wyoming, typical grasses found in this system include Pseudoroegneria spicata, Schizachyrium scoparium, Hesperostipa neomexicana, Hesperostipa comata, and species of Poa. Typical adjacent ecological systems include foothill shrublands, ponderosa pine savannas, juniper savannas, as well as shortgrass prairie.

Usually occurrences of this system have multiple plant associations that may be dominated by Andropogon gerardii, Schizachyrium scoparium, Nassella viridula, Pascopyrum smithii, Sporobolus cryptandrus, Bouteloua gracilis, Hesperostipa comata, or Hesperostipa neomexicana. In Wyoming, typical grasses found in this system include Pseudoroegneria spicata, Schizachyrium scoparium, Hesperostipa neomexicana, Hesperostipa comata, and species of Poa.

This ecological system occurs between 1600 and 2200 m in elevation. It is best characterized as a mixedgrass to tallgrass grassland on mostly moderate to gentle slopes, usually at the base of foothill slopes, e.g., the hogbacks of the Rocky Mountain Front Range where it typically occurs as a relatively narrow elevational band between montane woodlands and shrublands and the shortgrass steppe and mixedgrass prairie, but extends east on the Front Range piedmont alongside the Chalk Bluffs near the Colorado-Wyoming border, out into the Great Plains on the Palmer Divide, and on piedmont slopes below mesas and foothills in northeastern New Mexico. This mixed grassland receives more precipitation than shortgrass steppe or occurs on coarser-textured substrates allowing for increased infiltration and water storage (Noy-Meir 1973). A combination of increased precipitation from orographic rain, temperature, and soils limits this system to the lower elevation zone with approximately 40 cm of precipitation/year. It is maintained by frequent fire and associated with well-drained clay soils. Typical adjacent ecological systems include foothill shrublands, ponderosa pine savannas, juniper savannas, as well as shortgrass prairie.

Relatively frequent surface fire (FRI = 20 years -15 years in the southern extent) maintains this ecosystem by reducing seedling survival of shrubs such as Cercocarpus montanus and Rhus trilobata and trees such as Pinus ponderosa, Pinus edulis, and Juniperus spp. thus preventing conversion to shrublands and woodlands (Landfire 2007a). There is little information on this natural frequency, size, intensity, or severity of fire in this ecosystem. Ungulate grazing (Landfire 2007a) and herbivory are a key process that includes grazing and browsing by large and small mammals and insects. Soils are naturally disturbed by burrowing mammals such as prairie dogs, rabbits, pocket gophers, ground squirrels, and badgers providing habitat for disturbance-dependent species. Drought occurs periodically (approximately every 20-50 years) and can cause shifts in species compositions to more drought-tolerant species (Landfire 2007a).

This system is one of the most severely altered systems in the Southern Rocky Mountains ecoregion. Alteration is due to fire suppression, housing and water developments, conversion to hay meadows, overgrazing, etc. Fire suppression has allowed for shrub and tree invasion into the grassland and alters the species composition as well (Mast et al. 1997, 1998). Housing and water developments severely fragment and usually destroy the habitat, while agricultural use has converted tall grass prairies into hay meadows dominated by exotic grasses, e.g., Bromus inermis. It is very unusual to find excellent occurrences of this system. Threats are very high for this system and, therefore, a premium is set on protecting the existing occurrences (CNHP 2010b).

Conversion of this type has commonly come from urban and exurban development along the Front Range, water developments/reservoirs, and dryland wheat and irrigated agriculture especially hay meadows dominated by non-native forage grasses (CNHP 2010b). Fire suppression has allowed succession and conversion to shrublands and conifer woodlands especially from ponderosa pine, pinyon or juniper tree invasion (Mast et al. 1997, 1998). Common stressors and threats include fragmentation from housing and water developments, altered fire regime from fire suppression and indirectly from livestock grazing and fragmentation, introduction of invasive non-native species (CNHP 2010b). Potential climate change effects could include a change in the current extent of the ecosystem with lower elevation transitional areas converting to shortgrass prairie, if climate change has the predicted effect of less effective moisture with increasing mean temperature (TNC 2013).

This mixed grassland ecological system occurs in a transitional band between the Rocky Mountains and the Shortgrass Steppe where increased soil moisture from orographic lifting and local topography favor tall and mid-height grasses. The band is restricted to the Rocky Mountain foothills and piedmont and adjacent plains, extending farther east on the Palmer Divide, north alongside the Chalk Bluffs near the Colorado-Wyoming border, and south on and below mesas and escarpments in southeastern Colorado, northeastern New Mexico, and the panhandles of Oklahoma and Texas. These grasslands also occur around the edges of the Black Hills uplift, where Schizachyrium scoparium is the dominant grass.