Gravelly Pinedale Plateau (Gr PP)

Description

The Reference State is comprised of one plant community, the Bunchgrass Plant community.
The dominant grass is Bluebunch wheatgrass (Pseudoroegnaria spicata). Shrubs are sub-dominant and predominantly include fringed sagewort (Artemisia frigida), winterfat (Krascheninnikovia lanata), and Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis). Wyoming big sagebrush is typically absent on windward aspects (westerly) and present on leeward aspects (easterly). Forbs are sub-dominant and predominantly include pussytoes (Antennaria spp.), buckwheat (Eriogonum spp.), and Hood's phlox (Phlox hoodii).
Because this site is grass dominated, reference conditions do not result in disturbances that shift plant community phases.

Characteristics and indicators

This site occurs mostly on summits and shoulders, and often on windblown slopes. It is characterized by large rock fragments on the surface, typically alluvium (gravels and cobbles). Due to its landscape position, bunchgrasses dominate in the reference state, predominantly bluebunch wheatgrass, with scattered Wyoming big sagebrush on leeward and north-facing slopes.
A common scenario is a one to three inch sandy loam cap over loamy or sandy clay loam. When that cap is thicker (3 inches), needle and thread can replace bluebunch wheatgrass as the the dominant mid-stature bunchgrass.

Resilience management

This site has moderate to moderately high resilience due to its aridic ustic (ustic bordering on aridic) soil moisture regime and frigid bordering on cryic temperature regime (Chambers et.al. 2014). Precipitation is typically low, but more effective with cooler temperatures and present when needed during the critical growth period (May through June). The site can usually recover after disturbance but is susceptible to delays in recovery during extreme climatic events such as drought.

The site has moderately high resistance to invasion by annual grasses because of climate limitations (dry and cold). The site is more susceptible to invasion after extreme disturbance during warmer climatic periods and on southeast aspects and concave micro-topography.

At the LRU scale, this site is less resilient than Sandy, Loamy, or Clayey sites and is also less resistant to invasion by annual invasive grasses. Lower resilience and resistance is caused by lower production potential, low available water-holding capacity (AWC), coarser soil textures, and high amounts of rock fragment at the surface, making this site more susceptible to hot and dry drought conditions and harder for perennial plants to become established.

Submodel

Description

The Grazing Resistant State is characterized by dominance of Sandberg bluegrass and mat-forming forbs. Mid-size cool-season bunchgrasses have become scarce or absent, and an adequate seedbank does not exist for recovery to the Reference State. This state has one plant community, the Short-stature Grass/Mat-forming Forb Plant Community.

Characteristics and indicators

The site crosses the threshold to the Grazing Resistant State from the Reference State when desirable mid-stature bunchgrasses lose dominance. Once bluebunch wheatgrass becomes scarce for a longer time period, it is unlikely to have a sufficient seedbank to recover dominance in a reasonable time frame without extra energy being added to the system. It is characterized by decreased productivity, increased short-stature grasses, and high foliar cover of mat-forming forbs.

The Grazing Resistant State is very resistant to change, and therefore common on the landscape. In many cases, the transition to the Grazing Resistant State may have occurred many decades ago during an era of high stocking rates and continuous grazing. Sandberg bluegrass and rhizomatous wheatgrasses are low in stature and highly grazing tolerant. Rhizomatous species can form mats that provide soil protection by protecting the soil from raindrop impact, decreasing the risk of further soil erosion. High amounts of surface rock fragments can further armor this site from soil erosion.

Resilience management

Site resilience is lower than the Reference State. Site hydrology has been modified due to moisture being utilized by shallower rooting species. Therefore, the site is drier earlier in the season, lower in diversity, and unable to recover as quickly after a disturbances such as drought. This state is more drought-prone, and therefore sees wider productivity swings during dry versus wet years.
Site resistance to invasion by annual grasses is similar to the reference state, although there are more niches for undesirable annual forbs such as desert alyssum or annual invasive grasses such as cheatgrass to become established during warmer climatic periods and on southeast aspects and concave micro-topography.

Submodel

Description

The Disturbed State is a result of extreme soil-disturbing activities outside of the normal disturbance regime expected for this site. Primary examples include road construction, oil and gas exploration, as well as livestock and recreation heavy use areas.

Characteristics and indicators

Primary indicators of this state are extreme soil disturbance associate with anthropogenic activities. Depending on the time since disturbance, recent climatic events, and reclamation efforts, the plant community could be dominated by annual weeds or it could be reclaimed to a variety of introduced or native species.

Resilience management

Site resilience is lower than the Reference State, but potentially higher than the Grazing Resistant. Site stability and hydrology modifications exist, but may be temporary if proper reclamation occurs.
Site resistance to invasion by annual forbs and annual invasive grasses (cheatgrass) is lower due to an increase in soil disturbance allowing niches in the understory for establishment. Common annuals to invade this site include kochia, Russian thistle, and halogeton. Cheatgrass may be present and has the potential to dominate the site when it occurs on southeast aspects and on concave micro-topography.

Submodel