Loamy Argillic Bear River Valley 10-14" P.Z.

Description

The Reference State consists of two communities: the Early Sagebrush/Bunchgrass Community (1.1.1), and the Bunchgrass/Early Sagebrush Community (1.1.2). Each community differs in percent composition of bunchgrasses and percent shrub canopy cover. Shrub canopy cover is typically less than 25 percent. The dominant shrub species is early sagebrush. Forbs are a minor component on this site, and many are ephemeral, quickly performing their life cycle during favorable conditions in the spring. Some forb species may also experience prolonged dormancy during drought (Lesica and Steele 1994), making trend monitoring on this site difficult.

Two important processes occur in the reference state and result in plant community changes: 1) sagebrush-killing disturbances such as herbivory, drought, and prolonged soil saturation; and 2) time without those disturbances, generally referred to as "natural succession."

Characteristics and indicators

The shift between plant community phases is dependent upon sagebrush-killing disturbances, and without them it will increase even with proper grazing management. Improper grazing management may accelerate the rate of increase for the shrub component.
Management actions or treatments are not prescribed or used to mimic the natural disturbance regime due to fragile nature of the soils and lower productivity potential on this site. Prescribed fire is not used due to land use and ownership patterns and lack of fine fuels (Clause and Randall 2014).

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.

At the LRU scale, this site is less resilient than Sandy, Loamy, or Clayey ecological sites, but is more resistant to invasion by annual invasive grasses. Lower resiliency and higher resistance is caused by heavier soil textures and reduced infiltration, making this site more susceptible to dry and drought conditions and harder for new plants to become established.

Submodel

Description

The Grazing Resistant State (1.2) is characterized by early sagebrush dominance with an herbaceous layer dominated by Sandberg bluegrass, rhizomatous wheatgrasses, and a varying shrub component. Mutton bluegrass, Indian ricegrass and Letterman’s needlegrass have become scarce or absent. This state has one plant community, Early Sagebrush/Rhizomatous Wheatgrass Plant Community (1.2.1).

Characteristics and indicators

The site crosses the threshold to the Grazing Resistant State (1.2) from the Reference State (1.1) when desirable mid-stature grasses lose dominance. Once the key species become scarce, it is unlikely that they have sufficient reproductive capability (seed source, tillering, or re-sprouting) to recover dominance in a reasonable time frame without extra energy being added to the system. Minor soil degradation often occurs to prevent restoration to the Reference State.

The Grazing Resistant State is very resistant to change, and therefore common on Loamy Argillic sites in this MLRA. In many cases, the transition to the Grazing Resistant State may have occurred many decades ago during the era of high stocking rates and continuous grazing. While dominance by rhizomatous grasses makes the return to the Reference State difficult, it also makes the site resistant to further degradation. 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. However, overall soil health is lower than the reference state, primarily due to a reduction in soil organic matter and minor soil losses and degradation. Reduced soil organic matter is due to a reduction in litter. Decreased infiltration is due to shallower rooting depths and increased runoff. High intensity continuous or early season grazing puts this State at risk of transition to the Eroded 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, existing sagebrush canopy and remnant perennial vegetation provide some amount of resiliency. Rhizomatous grasses form mats that provide soil protection by protecting the soil from raindrop impact, decreasing the risk of soil erosion. However, overall soil stability is lower than the Reference State, primarily due to a reduction in soil organic matter due to a reduction in litter.
Site resistance to invasion by annual grasses is similar to the Reference State, although there are more niches for plants to become established during favorable conditions.

Submodel

Description

The Disturbed State is a result of soil-disturbing activities outside of the normal disturbance regime expected for this site. Examples are high intensity hoof action, anthropogenic activity, rodent activity, or frequent flooding, which includes occasional irrigation. It may also occur after high intensity wildfire or mechanical brush management preceded or followed by improper grazing techniques that include high-intensity grazing use without appropriate recovery periods.

Mechanical brush management treatment methods include heavy equipment for construction or mowing, chaining, or harrowing type sage treatment. Catastrophic wildfire could be a factor in maintaining this plant community by stimulating sprouting shrubs (rabbitbrush) and killing sagebrush, although it is rare on this site due to low fine fuel production.

Removal of shrubs without proper grazing management can lead to an increase in bare ground and erosion of the upper soil horizon. Consequences of this are decreased soil organic matter and soil erosion, soil crusting, and a decrease in soil surface aggregate stability.

Characteristics and indicators

There is a shift toward sprouting shrub dominance or co-dominance with big sagebrush depending on how long it has been since the disturbance(s). Green rabbitbrush is the dominant sprouting shrub. Along with a shift in shrub species, the herbaceous under-story also shifts toward more disturbance tolerant species such as western wheatgrass.

Resilience management

Site resilience is lower than the Reference State or Grazing Resistant State, but higher than the Invaded 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. However, existing sagebrush canopy and remnant perennial vegetation provide some amount of resiliency. Site resistance to invasion by annual grasses is lower due soil disturbances that allow niches in the under-story for establishment. However, the wetter spring conditions and prolonged dry conditions during the summer and fall are not a hospitable environment.

Submodel

Description

This state occurs when the "A" soil horizon has been lost and the subsoil is exposed, bringing the heavy clay soil layer closer to the surface.

Characteristics and indicators

There will be indicators of reduced soil and site stability as well as reduced hydrologic function, mainly water flow patterns, pedestals, rills, and gullies. Bare ground increases along with plant gap inter-space. Soil surface loss and degradation has occurred. Biotic integrity is affected by missing functional/structural groups and the loss of species diversity within functional/structural groups.

The site experiences little fluctuation in annual production from year to year because it is basically a monoculture of early sagebrush. The site is less diverse with lower quality habitat for wildlife and pollinators.

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. Soil loss and degradation prevents natural regeneration or restoration of the site.

Submodel