Rocky Mountain Foothill Shrubland

This ecological system is found in the foothills, canyon slopes and lower mountains of the Rocky Mountains and on outcrops and canyon slopes in the western Great Plains. It ranges from southern New Mexico, extending north into Wyoming, and west into the Intermountain West region. These shrublands occur between 1500 and 2900 m elevation and are usually associated with exposed sites, rocky substrates, and dry conditions, which limit tree growth. It is common where Quercus gambelii is absent, such as the northern Colorado Front Range and in drier foothills and prairie hills. This system is generally drier than Rocky Mountain Gambel Oak-Mixed Montane Shrubland (CES306.818) but may include mesic montane shrublands where Quercus gambelii does not occur. Cercocarpus montanus dominates pure stands in parts of Wyoming and Colorado. Scattered trees or inclusions of grassland patches or steppe may be present, but the vegetation is typically dominated by a variety of shrubs, including Amelanchier utahensis, Cercocarpus montanus, Purshia tridentata, Rhus trilobata, Ribes cereum, Symphoricarpos oreophilus, or Yucca glauca. Grasses are represented as species of Muhlenbergia, Bouteloua, Hesperostipa, and Pseudoroegneria spicata. Fires play an important role in this system as the dominant shrubs usually have a severe die-back, although some plants will stump sprout. Cercocarpus montanus requires a disturbance such as fire to reproduce, either by seed sprout or root-crown sprouting. Fire suppression may have allowed an invasion of trees into some of these shrublands, but in many cases sites are too xeric for tree growth. In Wyoming, stands where Cercocarpus montanus is a component of mixed shrublands are placed in Northern Rocky Mountain Montane-Foothill Deciduous Shrubland (CES306.994).

Cercocarpus montanus dominates pure stands in parts of Wyoming and Colorado. Scattered trees or inclusions of grassland patches or steppe may be present, but the vegetation is typically dominated by a variety of shrubs, including Amelanchier utahensis, Cercocarpus montanus, Purshia tridentata, Rhus trilobata, Ribes cereum, Symphoricarpos oreophilus, or Yucca glauca. Grasses are represented as species of Muhlenbergia, Bouteloua, Hesperostipa, and Pseudoroegneria spicata.

This ecological system is found in the foothills, canyon slopes and lower mountains of the Rocky Mountains and on outcrops and canyon slopes in the western Great Plains. It ranges from southern New Mexico, extending north into Wyoming, and west into the Intermountain West region. These shrublands occur between 1500 and 2900 m elevation and are usually associated with exposed sites, rocky substrates, and dry conditions, which limit tree growth. It is common where Quercus gambelii is absent, such as the northern Colorado Front Range and in drier foothills and prairie hills.

Fires play an important role in this system as the dominant shrubs usually have a severe die-back, although some plants will stump sprout. Cercocarpus montanus requires a disturbance such as fire to reproduce, either by seed sprout or root-crown sprouting. Fire suppression may have allowed an invasion of trees into some of these shrublands, but in many cases sites are too xeric for tree growth.

LANDFIRE developed a state-and-transition vegetation dynamics VDDT model for this system which has five classes in total (LANDFIRE 2007a, BpS 2810860). These are summarized as:

A) Early Development 1 All Structures (grass-dominated - 15% of type in this stage): Grass cover is 0-10%. Early succession, usually after moderately frequent stand-replacement fires; grasses and forbs dominant.

B) Mid Development 1 Closed (shrub-dominated - 15% of type in this stage): Shrub cover is 11-80%. Greater than 10% shrub cover (i.e., line intercept method) by weakly sprouting and seed-producing shrubs; grasses/forbs dominant in scattered openings.

C) Mid Development 1 Open (10% of type in this stage): Shrub cover is 0-10%, with grasses/forbs dominant in extensive openings.

D) Late Development 1 Open (10% of type in this stage): Shrub cover is 0-10%, with over-matured shrubs as patchy dominant overstory (e.g., in rock outcrops); grasses/forbs dominant in extensive openings.

E) Late Development 1 Closed (shrub-dominated - 50% of type in this stage): Shrub cover is 11-80%. Greater than 10% shrub cover; all age classes present but dominated by over-matured shrubs (e.g., in rocky draws).

Historically, this type may have been in a Fire Regime IV or II -- primarily moderate-interval (e.g., 20-50 years) stand-replacement fires in the shrub-dominated layer. Nearly all the dominant species in this BpS have the capability to resprout after disturbance (LANDFIRE 2007a, BpS 2810860).

Threats and stressors to this shrubland system include altered fire regime, fragmentation from roads and development near urban areas, mining, invasive species, livestock grazing disturbance or other human disturbances (CNHP 2010). These disturbances can cause significant soil loss/erosion and negatively impact the water quality within the immediate watershed. Invasive exotic species such as Bromus tectorum can become abundant in disturbed areas and alter floristic composition and provide fine fuels that many increase fire frequency and severity beyond the natural range of variation.

This system is found in the foothills, canyon slopes and lower mountains of the Rocky Mountains and on outcrops and canyon slopes in the western Great Plains. It ranges from southern New Mexico, extending north into Wyoming, and west into the Intermountain West region.