Gravelly Bear River Valley 10-14" P.Z.

Description

The Reference State consists of one plant community, the Bunchgrass Plant Community (1.1).

The dominant grass is bluebunch wheatgrass (Pseudoroegneria 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).

Resilience management

This site has moderate resilience due to its xeric soil moisture regime and frigid temperature regime (Chambers et.al. 2014). Precipitation is typically adequate and more effective with cooler temperatures, but timing of precipitation lowers resilience. Moisture is often not present when needed to support recovery efforts. The site can usually recovery after disturbance but is susceptible to delays in recovery during extreme climatic events such as drought.

The site has moderately low resistance to invasion by annual grasses because of climate suitability. Winter precipitation patterns favor annual invasion while cooler temperatures provide some resistance. The site is susceptible to invasion during hotter climatic periods.
On the LRU scale, this site is lower in resistance to invasives when it occurs on southern aspects due to the coarse surface textures and rock fragments.

Submodel

Description

The Grazing Resistant State has seen a shift in functional/structural group dominance. Due to herbivory pressure, there is a shift from mid-stature cool-season bunchgrasses to short-stature cool-season bunchgrasses such as Sandberg bluegrass and rhizomatous wheatgrasses like thickspike wheatgrass and western wheatgrass. Mat-forming forbs such as pussytoes (Antennaria spp.), Hood's phlox (Phlox hoodii), and buckwheat (Eriogonum spp.) increase and can become dominant.

Characteristics and indicators

There are fewer mid-size bunchgrasses and they are typically found under shrub canopy, when present, where they are protected from herbivory. The shrub canopy inter-spaces are occupied by grazing tolerant grasses as well as mat-forming forbs that, combined with surface rock fragments, armor the site from soil erosion.
Drier site conditions result in lower productivity and less herbaceous production potential. Decreased infiltration is caused by increased mat-forming forbs and lack of litter that acts as mulch in retaining soil moisture and retarding runoff.
In many cases, the transition to the Grazing Resistant State may have occurred many decades ago during an era of higher stocking rates and continuous grazing during the growing season. However, continual grazing during the critical growth period (roughly May-June) at proper stocking rates will facilitate the transition to this state and maintain it as a stable state.

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 and unable to recover as quickly after a disturbance. This state is more drought-prone, and therefore more vulnerable to invasion by annual invasive species. However, mat-forming forbs provide some amount of resiliency.
Site resistance to invasion by annual grasses is lower due to niches in the under-story for establishment as well as site water availability during the time suited for winter annuals such as cheatgrass (Bromus tectorum). Episodic and limited moisture is more suited to annual life forms.

Submodel

Description

The Invaded State has seen a shift in dominance toward annual invasive grasses. It often occurs after a disturbance that occurs in conjunction with drought conditions. Anthropogenic activity such as a gravel pits that are abandoned can lead to this state.

Characteristics and indicators

In this state, sagebrush canopy varies, but the under-story is dominated by annual invasive and weedy species. Biotic integrity is affected by functional/structural groups not expected for the site, invasive plants, and the loss of perennial species and functional/structural groups.

The site is more prone to drought with large fluctuations in annual production in response to weather events. The site is less diverse with lower quality habitat for wildlife and pollinators, and the risk of wildfire is increased from fine fuel production.

Resilience management

Site resilience is lower than all other states because the site hydrology has been modified resulting in greater runoff during spring melt and rainfall events. Therefore, the site is drier and unable to recover as quickly after a disturbance. Site resistance to invasion by annual grasses is lost due to niches in the under-story for establishment as well as site water availability during the time suited for winter annuals such as cheatgrass (Bromus tectorum). Episodic and limited moisture is more suited to annual life forms.

Submodel