State 1
Reference

Community 1.1
Bunchgrass/Winterfat

The Limy site potential is less than the Loamy and Loamy Calcareous site in this LRU, due to the restrictive nature of the calcium carbonate levels that occurs on it. The Bunchgrass/Winterfat Plant Community is well adapted to Cool Central Desertic Basins and Plateaus climatic conditions. The diversity in plant species allows for drought tolerance, and natural plant mortality is very low. These plants have strong, healthy root systems that allow production to increase with favorable moisture conditions.

Plant litter is limited for soil building and moisture retention. However, plant litter is properly distributed with very little movement off-site.

This plant community provides for soil stability and a properly functioning hydrologic cycle. The soils associated with this site are somewhat limited in the amount of soil moisture it can hold due to the calcium carbonate levels throughout the soil profile, resulting in a unique plant community in this LRU.

The Bunchgrass/Winterfat Community (1.1) occurs sporadically across a landscape in a mosaic pattern intermixed mostly with the Loamy and Loamy Calcareous sites, and with other sites less frequently. This community can occur over long time periods with or without disturbances, but can be accelerated with added grazing and browsing pressure.

Cool season bunchgrasses are dominant in the Bunchgrass/Winterfat Community (1.1) with foliar cover ranging from 40% to 65%.

State 2
Grazed/Browsed

The Winterfat (Heavy Browse) Plant Community (2.1) is characterized by browsed winterfat, high bare ground and an herbaceous component dominated by thickspike wheatgrass and Sandberg bluegrass, with limited mid-stature bunchgrasses. Once mid stature bunchgrasses become scarce, it is unlikely there will be sufficient reproductive capability (seed source, tillering, or resprouting) to recover dominance in a reasonable time frame without extra energy being added to the system. The plant community is highly resistant to changes in composition, due to the dominance and competition of established grazing resistant species. However, the community can be restored to the Reference State over time with decreased herbivory, possibly seeding, and time.

Winterfat dominates with cover as high as 25% or higher. The dominant shrub/subshrub is Winterfat.

Production potential is lower than in Reference State (1), and is somewhat variable, fluctuating in response to drought and wet cycles. Lower soil organic matter content leads to lower soil stability than in the Reference State. Ground cover is reduced. Infiltration is lower than in the Reference State and the water cycle has reduced function due to decreased soil organic matter.

Community 2.1
Winterfat (heavy browse) Heavily browsed winterfat Thickspike and bluegrass understory High bare ground

The Winterfat (Heavy Browse) Plant Community (2.1) is characterized by browsed winterfat, high bare ground and an herbaceous component dominated by thickspike wheatgrass and Sandberg bluegrass, with limited mid-stature bunchgrasses. Once mid stature bunchgrasses become scarce, it is unlikely there will be sufficient reproductive capability (seed source, tillering, or resprouting) to recover dominance in a reasonable time frame without extra energy being added to the system. The plant community is highly resistant to changes in composition, due to the dominance and competition of established grazing resistant species. However, the community can be restored to the Reference State over time with decreased herbivory, possibly seeding, and time.

Winterfat dominates with cover as high as 25% or higher. The dominant shrub/subshrub is Winterfat.

Production potential is lower than in Reference State (1), and is somewhat variable, fluctuating in response to drought and wet cycles. Lower soil organic matter content leads to lower soil stability than in the Reference State. Ground cover is reduced. Infiltration is lower than in the Reference State and the water cycle has reduced function due to decreased soil organic matter.

Community 2.2
Bluegrass/Thickspike wheatgrass Bluegrass and thickspike dominant Scattered winterfat

The Bluegrass/Thickspike Wheatgrass Community (2.2) is characterized by an herbaceous component dominated by Sandberg bluegrass, thickspike wheatgrass, and/or mat-forming forbs, with limited mid-stature bunchgrasses. Once these key mid-stature species become scarce, it is unlikely to 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. The plant community is highly resistant to changes in composition, due to the dominance and competition of grazing tolerant species. However, the community may shift back to the Reference State (1) with grazing deferment followed by a grazing system that allows periodic rest during the critical growth period. Seeding may be needed to achieve desired results.
Sandberg Bluegrass (Poa secunda) and/or Thickspike wheatgrass (Elymus lanceolatus ssp. lanceolatus) dominate, and winterfat foliar cover is typically 10% to 20%. This plant community phase occurs with continued herbivory/browse after the herbaceous component has already been degraded.

Productivity is highly variable and fluctuates in response to drought and wet cycles. Production is similar to the Reference State (1), however, plant composition changes have occurred leading to lower soil organic matter content and therefore lower soil stability than in the Reference State.

Pathway 2.1A
Community 2.1 to 2.2

Winterfat (heavy browse) Heavily browsed winterfat Thickspike and bluegrass understory High bare ground

Bluegrass/Thickspike wheatgrass Bluegrass and thickspike dominant Scattered winterfat

Increase herbivory (spring, summer) The trigger for a community shift from the Winterfat (Heavy Browse) Community (2.1) to the Bluegrass/Thickspike Wheatgrass Community (2.2) is a decrease in herbaceous herbivory and increase in browsing of winterfat (change in season of use). Without a change in grazing regime, the existing understory will respond, but mid-stature bunchgrasses will not increase. Fire is not typically a driver in this State due to reduced fine fuels.

Pathway 2.2A
Community 2.2 to 2.1

Bluegrass/Thickspike wheatgrass Bluegrass and thickspike dominant Scattered winterfat

Winterfat (heavy browse) Heavily browsed winterfat Thickspike and bluegrass understory High bare ground

No disturbance, rest, deferment The trigger for a community shift from the Bluegrass/Thickspike Wheatgrass Community (2.2) to the Winterfat (Heavy Browse) Community (2.1) is an increase in spring/summer grazing in conjunction with winter/fall browsing animals. With relatively high amounts of nutrition in winterfat these areas tend to have higher winter use by wildlife, livestock and wild horses. (Rasmussen, 1986)

State 3
Disturbed

This state contains one community, the Salt-Desert Shrub Community (3.1). It is characterized by sparse herbaceous plant cover dominated by salt desert shrubs and bare ground.

Communities in the Disturbed State (3) have crossed a threshold because of soil erosion, loss of soil fertility, and/or degradation of soil properties. Soil erosion affects the hydrology, soil chemistry, soil microorganisms, and soil physics to the point where intensive restoration is required to restore the site to another state or community. Simply changing grazing management may not create sufficient change to restore the site within a reasonable period. It will require a considerable input of energy to move the site back to the Reference State (1).

The Disturbed State (3) is at risk of weed invasion due to the high percentage of bare ground, but climatic conditions contribute to higher resistance to invasion.

Community 3.1
Salt Desert Shrubs

Increase in shrub cover,
ATGA, PIDE4 and KRLA2
Decrease in bunchgrass cover


Herbaceous canopy cover in the Salt Desert Shrub Community (3.1) is significantly reduced. Annual production is less than half of the Bunchgrass/Winterfat Plant Community (1.1). Perennial grass species (e.g., Indian ricegrass, and bottlebrush squirreltail) may exist only in patches and are typically low in vigor. This community tends to be dominated by winterfat and Gardner’s saltbush (salt desert shrubs) (>25% cover) and bare ground often exceeds 40% in large patches in the interspaces of the shrub canopy (>6 foot canopy gap common). The majority of annual production is from salt-desert shrubs so this site provides very little value for grazing.

Sparse vegetation creates low levels of foliar and basal cover. This, in turn, leads to low litter production, which is combined with reduced ability to retain litter on site. Soil is exposed to wind and water erosion in the plant interspaces. These factors combine to create a decrease in soil organic matter. Reduced litter cover, combined with reduced herbaceous cover, results in higher soil temperature, poor water infiltration rates, and high evaporation, thus favoring species which are more adapted to drier conditions. Soil fertility is reduced, soil compaction is increased, and resistance to soil surface erosion has declined compared to the other states. This community has lost most, if not all, of the attributes of a functioning, healthy rangeland, including good infiltration, minimal erosion and runoff, nutrient cycling, and energy flow.

State 4
Highly disturbed

All sites may transition to this state following a severe soil disturbance such as oil and gas development or surface mining extraction.

Community 4.1
Reclaimed

Seeded with natives or non-natives
Decrease in shrubs

The Reclaimed Community (4.1) is highly variable based on weather conditions during restoration activities, the management practices used to implement the restoration, the seed mix, and timing/method of stockpiling topsoil during the disturbance. The most common scenario is a reclaimed oil and gas well pad planted to crested wheatgrass (Agropyron cristatum) without appropriate topsoil stockpiling. If topsoil is stockpiled, it may have been stored for too long and/or stored too deep resulting in fewer soil microorganisms. Over time, winterfat may spread into the reclaimed area, but the understory will be dominated by introduced species. Biological soil crusts are minimal, further exposing the soil surface to erosional forces as well as impairing carbon, nutrient, and water cycles.

Community 4.2
Annuals

Perennial natives are replaced with Annual grasses and forbs

The Annuals Community (4.2) occurs after severe disturbance, most often physical soil disturbance that removes all topsoil, but it can also occur as a transition from the Disturbed State (3) after severe drought, flooding, pests, or disease kills shrubs, leaving the site with no perennial vegetation. Populations of annual and/or invasive weeds reach critical levels and impact the ecological processes on the site until restoration of the site occurs. As part of succession, all sites that are severely disturbed go through this plant community as part of the restoration process, but the time spent in this community phase is largely dependent on the use of restoration Best Management Practices (BMPs) and climate cycles. Biological soil crusts are non-existant, further exposing the soil surface to erosional forces as well as impairing carbon, nutrient, and water cycles.

Transition T1A
State 1 to 2

Increased herbivory (concentrated winter) The drivers for transition from the Reference State to the Grazed/Browsed State are high intensity grazing (herbivory during spring/summer and/or browse during fall/winter) and/or severe drought. High rates of herbivory during spring/summer and/or drought can lead to a decline in palatable mid-stature bunchgrasses, mainly Indian ricegrass, a short-lived perennial that requires more frequent seed production to provide an adequate seedbank, and bottlebrush squirreltail, widely adapted to a wide range of ecological conditions (USDA, NRCS, 2018).As bunchgrasses diminish or die during periods of stress, low-stature bunchgrasses and rhizomatous grasses gain a competitive advantage, creating a shift in species composition towards less productive, shorter species. While bare ground may not change, the pattern of bare ground will shift to larger gaps in the canopy and fewer herbaceous plants between shrubs. Once mid-stature bunchgrasses species become scarce, it is unlikely that they have sufficient reproductive capability (seed source, tillering, or resprouting) to recover dominance in a reasonable time frame without management changes and extra energy being added to the system. When the understory vegetation has been degraded to this point, the transition to the Grazing/Browsed State (2) can occur from the Bunchgrass/Winterfat Plant Community (1.1). The transition is not dependent on the increase of shrub cover, but rather the lack of mid-stature bunchgrasses in the canopy interspaces. High rates of browse during fall/winter can lead to a decline in winterfat and an increase in bare ground. Often times this occurs at the same time as high levels of use in spring/summer associated with areas that have high wild horse use. Managing wild horse populations is critical to the heath of this site as it is highly preferred by this species. Management should focus on grazing management strategies that will prevent further degradation. This can be achieved through a grazing management scheme that is within the carrying capacity and varies the season of use to provide periodic deferment during the critical growth period (roughly May-June). Forage quantity and/or quality in the Grazing/Browsed State (2) may be substantially reduced compared to the Reference State, and will dramatically fluctuate in the dry vs. wet years.

Transition T1B
State 1 to 3

Soil disturbing activity (hoof action, anthropogenic activity, rodent activity) The driver for transition from the Reference State to the Disturbed State is a soil disturbing activity (hoof action, anthropogenic, rodent, etc.). Drought can accelerate this transition. In some instances, dissolved salts occur below the plant rooting zone, and with soil disturbance these salts are released and made available to plants. With the increase in salts, such as sodium, the plant community can be highly altered. When this happens, a threshold has been crossed and is extremely difficult to remedy. Indicators of this transition include significant declines in herbaceous cover and an increase in salt loving plants such as Gardner’s saltbush (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=ATGA" target="_blank" title="Open in plants.usda.gov"><i>Atriplex gardneri</i></a>). The trigger for this transition is a loss of “A” horizon material and an increase in dissolved salts, released from a deeper “B” horizon. Soil erosion is accompanied by decreased soil fertility driving the transitions to the Disturbed State. Several other key factors signal the approach of a threshold: an increase in soil dispersion (caused by increased sodium), a decrease in soil surface aggregate stability, and/or evidence of erosion, including water flow patterns, development of plant pedestals, and litter movement.

Restoration pathway R2A
State 2 to 1

Decreased herbivory (prescribed grazing practices), seeding time The drivers for this restoration pathway are restoration of native herbaceous species by grazing rest or deferment followed by changing the season of use from spring to fall, lowering stocking density, possible seeding of native herbaceous species, and time. If some mid-stature bunchgrasses remain in the understory, proper grazing management can move the site back to the Reference State (1). This could take multiple generations of management or could be accelerated with rest or deferment combined with successive wet springs conducive to seed germination and seedling establishment. (Derner, Schuman, Follett, & Vance, 2014).

Transition T2A
State 2 to 3

Soil disturbing activity (hoof activity, anthropogenic activity) The driver for transition from the Grazed/Browsed State to the Disturbed State (T2A) is an increase in salt-desert shrubs, caused by soil disturbance that frees up exchangeable sodium and other salts that occur with the subsurface soil horizons. Examples of soil disturbance include hoof action, recreation, small burrowing mammals, and high stocking densities. If depth to sodium affected subsurface soil horizon (>8mmhos/cm) is relatively shallow (<10cm), the risk of crossing this threshold increases. When this threshold is crossed, plant community dynamics are affected, bare ground increases, hydrology is changed due to the restrictive nature of the exchangeable sodium and runoff is increased. In these cases it may be impossible to recover from this threshold. Indicators of the Disturbed state are an increase in salt desert shrubs, such as; Gardner’s saltbush (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=ATGA" target="_blank" title="Open in plants.usda.gov"><i>Atriplex gardneri</i></a>) and spiny horsebrush (Tetradymia spinescens), and increased bare ground.

Transition T2B
State 2 to 4

The driver for transition from the Grazed/Browed to the Highly Disturbed State (T2B) is a topsoil removing event with mechanical equipment. Examples include construction sites, oil and gas activity, and borrow areas.

Restoration pathway R3A
State 3 to 2

If soil disturbance is minimal, Decreased herbivory (prescribed grazing practices), seeding time The drivers for this restoration pathway are decreased herbivory/browse, seeding and time, if soil disturbance has not completely altered to soil chemistry of the site (i.e. exposing the soil layer with exchangeable sodium and other salts). Due to loss of soil fertility, structure, and organic matter, reference community plants are slow to repopulate the site. Success of this restoration is highly dependent upon climatic factors such as drought.

Transition T3A
State 3 to 4

The driver for transition from the Disturbed State to the Highly Disturbed State (T3A) is a topsoil removing event with mechanical equipment. Examples include construction sites, oil and gas activity, and borrow areas.