State 1
Reference

Figure 7. Bunchgrass/Big Sagebrush Plant Community on the left (reclaimed pipeline route)

The Reference State consists of two plant communities: the Big Sagebrush/Bunchgrass Plant Community and the Bunchgrass/Big Sagebrush Plant Community. Each plant community differs in percent composition and foliar cover of bunchgrasses and Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) as the dominant shrub. Forbs are a minor component. Two important processes occur in the Reference State and result in plant community changes: 1) sagebrush-killing disturbances such as herbivory, drought, prolonged soil saturation, and to a lesser extent fire; 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 sagebrush 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.

Community 1.1
Big Sagebrush/Bunchgrass Plant Community

This community is well adapted to Eastern Idaho 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 significantly with favorable moisture conditions. Abundant plant litter is available for soil building and moisture retention. 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 Big Sagebrush/Bunchgrass Community can occur across the entire ecological site or can occur in a mosaic with the Bunchgrass/Big Sagebrush Community. This community can occur over time without these disturbances and accelerated with added herbaceous grazing pressure. Wyoming big sagebrush is dominant with foliar cover ranging from 15 to 25 percent. At this sagebrush canopy level in this precipitation zone, there is some competition between the shrub over-story and the herbaceous under-story. (Winward 2007) A Big Sagebrush/Bunchgrass Community with a degraded under-story is an “at-risk” community. There are generally few canopy gaps, and most basal gaps are moderate (3 to 6 feet). Rock cover on the soil surface is common and often armors the site against soil erosion. Many plant inter-spaces have canopy or litter cover. Production of grasses is lower than in the Bunchgrass/Big Sagebrush Community.

Community 1.2
Bunchgrass/Big Sagebrush Plant Community

Figure 9. Bunchgrass/Big Sagebrush on left (reclaimed pipeline route)

The Bunchgrass/Big Sagebrush Community can occur across the entire ecological site on a given landscape but more likely occurs in a mosaic pattern associated with the disturbance cycle at any given location. Mid-stature bunchgrasses dominate and sagebrush is sub-dominant with foliar cover ranging from 5 to 15 percent. At this sagebrush canopy level in this precipitation zone, there is little, if any, competition between the shrub over-story and the herbaceous under-story. In fact, there is evidence to suggest that the under-story receives more benefit from the sage over-story than negative effects. (Winward 2007). There are generally few canopy gaps, and most basal gaps are generally small (one to two feet). Rock cover on the soil surface is common. Most shrub inter-spaces have canopy or litter cover. Production of grasses is higher than in the Big Sagebrush/Bunchgrass Community.

Pathway 1.1A
Community 1.1 to 1.2

Sagebrush thinning event via climatic events such as drought, prolonged soil saturation, freeze-kill, snow mold, and herbivory.

Context dependence. Thinning events are often episodic with climatic events and can occur suddenly with a particular event (precipitation, temperature, insect irruption, etc.) or can be gradual over a period of years such as during prolonged drought/warm or wet/cool periods. A successful pathway is contingent upon a grazing regime that allows for periodic critical growth period rest (May through June). An integrated pest management plan is needed to prevent, avoid, manage, and suppress invasive species.

Pathway 1.2A
Community 1.2 to 1.1

Natural succession (time without sagebrush killing event).

Context dependence. Time period for pathway is dependent upon weather events such as drought and above normal precipitation years. Drought results in slower pathway while favorable precipitation can result in a faster pathway. A grazing regime that mimics the historic regime (light intensity, episodic grazing events) will not alter the pathway, but a continuous grazing regime at moderate to heavy intensity can accelerate the pathway.

State 2
Grazing Resistant

The Grazing Resistant State has seen a shift in under-story 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-stature bunchgrasses and they are typically found under the shrub canopy where they are protected from herbivory. The shrub canopy inter-spaces are occupied by grazing tolerant grasses as well as patches of bare ground that are sometimes connected. Canopy gaps and bare ground increase, while herbaceous foliar cover decreases. Drier site conditions result in lower productivity and less herbaceous production potential. Decreased infiltration is caused by increased bare ground patch size 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 through 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, 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 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.

Community 2.1
Big Sagebrush/Short-stature Grass Plant Community

This plant community is characterized as Wyoming big sagebrush dominated with a diminished under-story. The under-story has lost many of the mid-stature cool-season bunchgrasses, and they have been replaced with short-stature bunchgrasses such as Sandberg bluegrass, rhizomatous wheatgrasses, and mat-forming forbs. Shrub foliar cover is often greater than 15 percent and typically comprising over half of total annual production. Areas that catch and retain snow are more likely to have higher shrub cover. Herbaceous production and foliar cover has decreased. There are often small amounts of annual invasive grasses, mostly less than 5 percent foliar cover. There is often a slight increase in sprouting shrubs (less than 10 percent composition by weight). This plant community is at-risk of transitioning to the Invaded State with additional disturbance such as heavy grazing, sagebrush treatment, or ground-disturbing activity. Productivity is highly variable and fluctuates drastically in response to drought and wet cycles. Total annual production is lower than in Reference State (1), leading to lower soil organic matter content and therefore lower soil stability than in the Reference State. Total annual production ranges from 300 to 700 pounds per acre (lbs/ac) with a RV of 500 lbs/ac. Biotic integrity is affected by the change in functional/structural group dominance.

Community 2.2
Short-stature Grass/Big Sagebrush Plant Community

This plant community is characterized by a dominance of short-stature grasses such as Sandberg bluegrass, rhizomatous grasses and grass-likes, and mat-forming forbs. A sagebrush killing event has happened recently, and Wyoming big sagebrush foliar cover is typically less than 15 percent. There can be an initial flush of invasive annuals, mainly cheatgrass, within the first few years of a sagebrush killing event, but they are expected to reduce to less than 5 percent foliar cover. There is often a slight increase in sprouting shrubs (less than 10 percent composition by weight).Total annual production ranges from 300 to 700 pounds per acre (lbs/ac) with a RV of 500 lbs/ac. Biotic integrity is affected by the change in functional/structural group dominance. This plant community is at-risk of transitioning to the Invaded State with additional disturbance such as heavy grazing, sagebrush treatment, or ground-disturbing activity.

Pathway 2.1A
Community 2.1 to 2.2

Sagebrush killing event, mainly natural climatic events such as herbivory, drought, prolonged soil saturation, freeze-kill, or snow mold. Fire is not typically a driver in this state due to the lack of fine fuels in the under-story.

Context dependence. Killing events are often episodic with climatic events and can occur suddenly with a particular event (fire, precipitation, temperature, insect irruption, etc.). This pathway relies upon close to normal precipitation and temperature as well as a grazing regime that is low to moderate intensity. If extreme conditions/disturbances such as hot temperatures, drought, or high intensity grazing occur, there is risk of a transition to either the Disturbed State or Invaded State depending upon severity and cumulative disturbance.

Pathway 2.2A
Community 2.2 to 2.1

Natural succession (time without sagebrush killing event).

Context dependence. Time period for this pathway is dependent upon weather events such as drought and above normal precipitation years. Drought results in a slower pathway while favorable precipitation can result in a faster pathway. A grazing regime that mimics the historic regime (light intensity, episodic grazing events) will not alter the pathway, but a continuous grazing regime at moderate to heavy intensity can accelerate the pathway.

State 3
Disturbed

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 prolonged soil saturation, which includes occasional irrigation. It may also occur after brush management preceded or followed by improper grazing techniques that include high-intensity grazing use without appropriate recovery periods. Brush management treatment methods are typically chemical (including 2,4-D or tebuthiron) due to soil limitations to mechanical treatment. Herbivory (including browse and/or insects) can contribute to disturbances affecting this state. High intensity fire could be a factor in maintaining this plant community by stimulating sprouting shrubs (rabbitbrush) and killing sagebrush.

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). Both green and rubber rabbitbrush may be present. Along with a shift in shrub species, the herbaceous under-story also shifts toward more disturbance tolerant species such as rhizomatous wheatgrasses. Annual weeds such as bur buttercup, flixweed, and lambsquarter, and invasive annual grasses such as cheatgrass are are often present in small amounts (less than 5 percent composition by dry weight).

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 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 during drought.

Community 3.1
Big Sagebrush/Rabbitbrush Plant Community

This plant community is a result of recovery after a past soil-disturbing activity. It is co-dominated by sprouting shrubs, mainly green rabbitbrush (aka yellow rabbitbrush in USDA PLANTS) and Wyoming big sagebrush. The understory typically consists of a combination of perennial rhizomatous grasses, mainly western wheatgrass, and annual grasses and forbs. Total annual production ranges from 300 to 700 pounds per acre (lbs/ac) with a RV of 500 lbs/ac. The soil is is typically adequately protected, but erosion can occur during high runoff events. The biotic integrity is reduced due to low vegetative production, relative dominance and unexpected structural/functional groups, and potentially invasive species if present. The watershed is functioning-at-risk.

Community 3.2
Rabbitbrush/Rhizomatous Wheatgrass Plant Community

This plant community is the result of a recent soil-disturbing activity. Western wheatgrass is the dominant perennial grass, and annual grasses and forbs are often present. With sagebrush removed, green or rubber rabbitbrush is the dominant shrub, often exceeding 30 percent of the annual production. Subdominant under-story species include bottlebrush squirreltail, Sandberg bluegrass, and unpalatable annual and perennial forbs. In the absence of annuals, there can be a substantial amount of bare ground. Total annual production ranges from 300 to 700 pounds per acre (lbs/ac) with a RV of 500 lbs/ac. The soil is not adequately protected, and erosion is expected without management to allow for adequate litter and residual. The biotic integrity is reduced due to low vegetative production, relative dominance and unexpected structural/functional groups, and potentially invasive species if present. The watershed is functioning-at-risk.

Pathway 3.1A
Community 3.1 to 3.2

Sagebrush killing event, typically high intensity fire or anthropogenic soil disturbing activity.

Context dependence. Killing events are often episodic with climatic events and can occur suddenly with a particular event (fire, precipitation, temperature, insect irruption, etc.). If extreme conditions/disturbances such as hot temperatures, drought, or high intensity grazing occur, there is risk of a transition to the Invaded State depending upon severity and cumulative disturbance.

Pathway 3.2A
Community 3.2 to 3.1

Natural succession (time without sagebrush killing event).

Context dependence. Time period for pathway is dependent upon weather events such as drought and above normal precipitation years. Drought results in slower pathway while favorable precipitation can result in a faster pathway. A grazing regime that mimics the historic regime (light intensity, episodic grazing events) will not alter the pathway, but a continuous grazing regime at moderate to heavy intensity can accelerate the pathway.

State 4
Invaded

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.

Characteristics and indicators. In this state, sagebrush canopy varies, but the under-story is dominated by annual invasive and weedy species. There will be indicators of reduced soil and site stability as well as reduced hydrologic function, mainly water flow patterns and pedestals, but potentially rills and gullies. Soil surface loss and degradation is likely. 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.

Community 4.1
Big Sagebrush/Annual Plant Community

This plant community is often the result of improper grazing and historic disturbances. Improper grazing is defined as either high- or low-intensity grazing without the appropriate recovery period. Wyoming big sagebrush and rabbitbrush dominate with annual production often exceeding 40 percent. The under-story is dominated by annual grasses and forbs while perennial grass and forbs are sparse and bunchgrasses are limited to the protected areas under shrubs. The predominant perennial grasses include Sandberg bluegrass and rhizomatous wheatgrass (western wheatgrass). Total annual production ranges from 200 to 600 pounds per acre (lbs/ac) with a RV of 400 lbs/ac. Soil erosion is accelerated because of the lack of deep-rooted perennials. The biotic community has been compromised. The watershed is degraded. Water flow patterns and pedestals are obvious. Infiltration is reduced, and runoff is increased.

Community 4.2
Annual Plant Community

This plant community results from a severe sagebrush killing disturbance once a site has been invaded by annuals. Repeated disturbances, such as fire, can maintain this plant community, but that is a rare occurrence for this site. Otherwise, sagebrush will typically re-establish on this site fairly quickly, within 5 to 10 years. However, to achieve pre-disturbance sagebrush canopy levels will take much longer. This site has low potential for recovery once dominated by annuals. Seeding is recommended to restore herbaceous perennial functional structural groups. Productivity in this plant community phase is highly variable based on current year's weather, and can range from 200 pounds per acre (lbs./ac.) or less, and up to 600 lbs./ac., with representative value of 400 lbs./ac.

Pathway 4.1A
Community 4.1 to 4.2

Sagebrush killing event, typically catastrophic fire or soil disturbance)

Context dependence. Killing events are often episodic with climatic events and can occur suddenly with a particular event (fire, precipitation, temperature, insect irruption, etc.). Consecutive disturbances and extreme conditions such as hot temperatures, drought, or high intensity grazing will exacerbate this pathway to an annual dominated system.

Pathway 4.2A
Community 4.2 to 4.1

Natural succession (time without sagebrush killing event).

Context dependence. Time period for pathway is dependent upon weather events such as drought and above normal precipitation years. Drought results in slower pathway while favorable precipitation can result in a faster pathway. A grazing regime that mimics the historic regime (light intensity, episodic grazing events) will not alter the pathway, but a continuous grazing regime at moderate to heavy intensity can accelerate the pathway.

Transition T1A
State 1 to 2

Herbivory pressure in excess of normal Reference State conditions. A typical scenario is continuous spring or season-long grazing with low stocking intensity.

Constraints to recovery. Recovery is inhibited by continued herbivory pressure, reduced seedbank, and drought conditions. Annual grasses are likely in small amounts.

Context dependence. Drought and annual invasion are most likely variables to prevent restoration.

Transition T1B
State 1 to 3

Soil-disturbance outside of the normal disturbance regime expected for this site. Examples include high intensity fire, high intensity hoof action, anthropogenic activity (e.g. mechanical and/or chemical treatments), rodent activity, or prolonged soil saturation, which includes occasional irrigation.

Constraints to recovery. Recovery is inhibited by consecutive disturbances over a relatively short time period and drought conditions. Annual grasses are likely in small amounts, increasing with each additional disturbance.

Context dependence. Drought and annual invasion are most likely variables to prevent restoration.

Transition T2A
State 2 to 3

Soil-disturbance outside of the normal disturbance regime expected for this site. Examples include catastrophic wildfire, high intensity hoof action, anthropogenic activity (e.g. mechanical and/or chemical treatments), rodent activity, or prolonged soil saturation, which includes occasional irrigation.

Constraints to recovery. Recovery is inhibited by consecutive disturbances over a relatively short time period and drought conditions. Annual grasses are likely in small amounts, increasing with each additional disturbance.

Context dependence. Drought and annual invasion are most likely variables to prevent restoration.

Transition T2B
State 2 to 4

Extreme herbivory resulting in removal of perennial herbaceous vegetation followed by annual invasion, typically associated with post-drought conditions. It is common for this to occur without a sagebrush killing event, resulting in the shrub/annual plant community.

Constraints to recovery. Recovery is inhibited by fire risk and annual invasion.

Context dependence. Drought and annual invasion are variables that prevent restoration.

Transition T3A
State 3 to 4

Extreme disturbance, including catastrophic wildfire, drought, or other soil removal disturbance, resulting in removal of perennial vegetation followed by annual invasion, typically associated with post-drought conditions.

Constraints to recovery. Recovery is inhibited by fire risk and annual invasion.

Context dependence. Drought and annual invasion are variables that prevent restoration.