State 1
Bluebunch Wheatgrass/Mixed Shrub

The Reference State, State 1, is the Bluebunch Wheatgrass/Mixed Shrub State, in response to the dominance of bluebunch wheatgrass and other mid-stature cool-season bunchgrasses that are prominent in each community. Rhizomatous wheatgrasses and short-stature cool-season bunchgrasses are secondary in these communities. Sagebrush and rabbitbrush is present on the site, but is not the major cover class.

Characteristics and indicators. Bunchgrass/Sagebrush State (State 1 - Reference) is characterized by the key species including fifteen percent or less composition by cover of Wyoming big sagebrush, black sagebrush, and fringed sagewort; with 30 percent cover of bluebunch wheatgrass, rhizomatous wheatgrasses (Western and Thickspike), Indian ricegrass, and needle and thread. Minor component to the overall composition is made up of bottlebrush squirreltail, Sandberg bluegrass, mutton bluegrass, prairie junegrass, and threadleaf sedge.

Resilience management. This state occurs in areas that are grazed moderately with periods of rest by large ungulates include livestock (cattle and/or sheep) as well as antelope, deer, and elk. Prescribed grazing and drought planning allows this State to persist. The community is adaptable to drought with management.

Community 1.1
Bluebunch Wheatgrass/Rhizomatous Wheatgrasses

Figure 8. Bluebunch wheatgrass dominated community with spike fescue and Montana wheatgrass.

The interpretive plant community for the Shallow Igneous ecological site is the Bluebunch Wheatgrass/Rhizomatous Wheatgrasses plant community. This plant community evolved with grazing by large herbivores and periodic fires. This plant community can be found on areas that are properly managed with grazing, and on areas receiving occasional short periods of rest. Potential vegetation is about 75-80 percent grasses or grass-like plants, 10 percent forbs, and 10-15 percent woody plants. Mid-stature cool-season bunchgrasses dominate the community. The major grasses include bluebunch wheatgrass, needle and thread, Indian ricegrass, and rhizomatous wheatgrass. Other grasses occurring are Sandberg bluegrass, prairie junegrass, and bottlebrush squirreltail. Green needlegrass and spike fescue occur in the upper limit of this precipitation zone. Black and Wyoming big sagebrush are conspicuous elements of this state, which can make up 10percent of the annual production. A variety of forbs also occurs in this community phase and plant diversity is high (see Plant Composition Table). The total annual production (air-dry weight) of this state is about 500 pounds per acre, but it can range from about 325 lbs./acre in unfavorable years to about 700 lbs./acre in above average years.

Resilience management. The plant community is extremely stable and well adapted to the Central Rocky Mountains climate. The diversity in plant species allows for high drought resistance. This is a sustainable plant community (site/soil stability, watershed function, and biologic integrity).

Community 1.2
Perennial Grass/Mixed Shrub

Figure 11. Bluebunch wheatgrass and Wyoming big sagebrush community with bluegrass and needle and thread.

Historically, this plant community evolved under grazing and a low fire frequency. Currently, it is found under moderate, season-long grazing by livestock and will be exacerbated by prolonged drought conditions. This plant community is still dominated by cool-season grasses, while miscellaneous forbs account for the balance of the understory. A variety of shrubs is now a conspicuous part of the overall production. The dominant grasses include bluebunch and Montana wheatgrasses, rhizomatous wheatgrasses, and needleandthread. Grasses and grass-like species of secondary importance include prairie Junegrass, , Sandberg bluegrass, and threadleaf sedge. Green needlegrass and spike fescue occur on sites in the upper limit of this precipitation zone. Forbs commonly found in this plant community include pussytoes, buckwheat, hairy goldenaster, Indian paintbrush, and phlox. Big sagebrush, black sagebrush, and rabbitbrush dominate the overstory. Shrubs can make up to 20 percent of the annual production. The overstory of shrubs and understory of grass and forbs provide a diverse plant community. When compared to the Reference plant community, shrubs, prairie Junegrass, and threadleaf sedge have increased. Plains prickly pear cactus may also have invaded, but occurs only in small patches. Indian ricegrass, bluebunch and Montana wheatgrasses has decreased and Indian ricegrass may occur in only trace amounts under the sagebrush canopy or within the patches of prickly pear. The total annual production (air-dry weight) of this state is about 400 pounds per acre, but it can range from about 200 lbs./acre in unfavorable years to about 600 lbs./acre in above average years.

Resilience management. This plant community is resistant to change. The herbaceous species present are well adapted to grazing; however, species composition can be altered through long-term overgrazing. The herbaceous component is mostly intact and plant vigor and replacement capabilities are sufficient. Water flow patterns and litter movement may be occurring but only on steeper slopes. Incidence of pedestalling is minimal. Soils are mostly stable and the surface shows minimum soil loss. The watershed is functioning and the biotic community is intact.

Pathway 1.1A
Community 1.1 to 1.2

Bluebunch Wheatgrass/Rhizomatous Wheatgrasses

Perennial Grass/Mixed Shrub

Moderate, continuous season-long grazing will convert the plant community to the Perennial Grass/Mixed Shrub Plant Community. Prolonged drought will exacerbate this transition.

Pathway 1.2A
Community 1.2 to 1.1

Perennial Grass/Mixed Shrub

Bluebunch Wheatgrass/Rhizomatous Wheatgrasses

Prescribed grazing or possibly long-term prescribed grazing, will convert this plant community to the Reference plant community (1.1). The probability of this occurring is high especially if rotational grazing along with short deferred grazing is implemented as part the prescribed method of use. Brush treatment can be useful to hasten this transition if desired.

State 2
Mixed Shrub/Bare Ground

Shrubs or woody vegetation creates a niche for most herbaceous understory to persist and maintain some vigor in difficult conditions by utilizing the moisture and shelter provided by the canopy as well as protection from grazing. Persistence of drought and/or frequent over use by livestock and wildlife leads to a decline of the herbaceous species, creating the Mixed Shrub/Bare Ground state. This State can be exacerbated by insects and other human disturbances.

Characteristics and indicators. There is a high level of variability of species in this State, that will shift in response to precipitation and to past management. Only one defined community will be provided, with discussion of transitions or variances from this community. The total woody canopy cover does not necessarily always increase with this community, but the percent composition by cover and production is swayed by the decrease of herbaceous vegetation and the relative stability of production by the woody species, creating the appearance of increased canopy by sagebrush.

Resilience management. Risk of wildfire within this state is minimal due to the lack of fine fuels within the understory, but the canopy of the woody vegetation can easily carry a fire under certain climatic conditions. Depending on the prescription of use, trailing and other erosional patterns are highly visible in this State. Protection from wildfire and use, on a long-term perspective can aid in the transition of the Reference Communities (1.1 or 1.2) to this State as shrubs reach maturity reducing the ability for the herbaceous component to maintain vigor; leading to a high rate of bare ground and shrub cover. As the herbaceous cover declines and the site continues to weaken, the woody cover is susceptible to attack by insects, disease, and general old age that can remove it from the system creating a system that is at risk of invasion or transition to a more degraded State.

Community 2.1
Mixed Shrub/Bare Ground Community

Figure 14. Sagebrush is dominant with only remnants of the perennial grasses remaining.

This plant community is the result of frequent and severe grazing and protection from fire. Soils on these sites are typically low in soluble salts. Shrubs and especially sagebrush dominate this plant community, as the annual production of sagebrush exceeds 20 percent.. Shrubs are significant components of the plant community and the preferred cool season grasses have been eliminated or greatly reduced. The dominant grasses/grass-likes are prairie junegrass, Sandberg bluegrass, and threadleaf sedge. Cactus often invades. The interspaces between plants have expanded leaving the amount of bare ground more prevalent. As compared with the Reference Plant Communities (1.1 or 1.2), the annual production is reduced, but the shrub production compensates for some of the decline in the herbaceous production. The total annual production (air-dry weight) of this state is about 275 pounds per acre, but it can range from about 175 lbs./acre in unfavorable years to about 375 lbs./acre in above average years.

Resilience management. Rangeland Health Implications/Indicators: This plant community is resistant to change as the stand becomes more decadent. These areas may actually be more resistant to fire as less fine fuels are available and the bare ground between the sagebrush plants is increased. Continued frequent and severe grazing or the removal of grazing does not seem to affect the composition or structure of the plant community. Plant diversity is moderate to poor. Soil erosion is accelerated because of increased bare ground. Water flow patterns and pedestalling are obvious. Infiltration is reduced and runoff is increased. Rill channels may be noticeable in the interspaces and gullies may be establishing where rills have concentrated down slope.

State 3
Sod-former

The Sod-former State is a low-stature community that has shifted from the cool-season bunchgrasses to tillering grass-likes (threadleaf sedge). Fringed sagewort and pricklypear cactus are common.

Characteristics and indicators. The prominent cover is threadleaf sedge. Scattered sagebrush may persist with rubber rabbitbrush and skunkbush sumac. Season of use and species of grazing ungulate will be a factor affecting this cover. The shift in hydrology of this State leads to low vigor shrubs. Most other mid-stature cool-season bunchgrasses are limited to within the canopy of the sagebrush or within the protective cactus clumps.

Resilience management. The dense root map of threadleaf sedge makes this State extremely resistant to change, and resilient to disturbance. Although the establishment of threadleaf sedge is a slow process, it will become a near monoculture stand. Removal of grazing or disturbance does not provide a shift in the herbaceous cover within this community. The overall health and vigor of both the herbaceous as well as woody cover will improve with the removal of the grazing pressure or disturbance from the community.

Community 3.1
Threadleaf Sedge Sod

Figure 17. Threadleaf sedge has become the dominant cover with scattered cover of sagebrush and rabbitbrush.

This plant community is the result of frequent and severe year-long grazing, which has adversely affected the perennial grasses as well as the shrub component. Other factors that can affect the shrubs include drought, heavy browsing, wildfires, and/or human brush control measures. A dense sod of threadleaf sedge dominates this site. Prickly pear cactus can become dense enough in patches so that livestock cannot graze forage growing within the cactus clumps. Sagebrush has been significantly reduced and in some cases removed. When compared to the Reference Plant Community, threadleaf sedge has increased. All mid-stature cool-season bunchgrasses and forbs have been greatly reduced and the shrub component is lacking. Total production has been significantly decreased. The total annual production (air-dry weight) of this state is about 150 pounds per acre, but it can range from about 100 lbs./acre in unfavorable years to about 250 lbs./acre in above average years.

Resilience management. This sod is extremely resistant to change and continued frequent and severe grazing or the removal of grazing does not seem to affect the plant composition or structure of the plant community. The biotic integrity of this state is not functional and plant diversity is extremely low. This sod bound plant community is very resistant to water infiltration. While this sod protects the site itself, areas amid these patches or off-site areas are affected by excessive runoff that can cause rills and gully erosion. Water flow patterns are obvious in the bare ground areas and pedestalling is apparent along the sod edges. Rill channels are noticeable in the interspaces and down slope. The watershed may or may not be functioning, as runoff may affect adjoining sites.

State 4
Invaded

The transition into the Invaded State, is typically a result of wildfire, a failed controlled burn or other event that removes the sagebrush from the site and allows a readily available seed bank or seed source of the undesirable species to flourish.

Characteristics and indicators. The most common invasive community that is found in the foothills and through the Big Horn Basin and much of the surrounding regions is Cheatgrass. However, there are other threats present, such as thistles, that can develop into near monoculture stands. The loss of diversity, changes to the potential of a site due to allelopathy or other deterrent characteristics of invasive species, and risks or land use capabilities associated with the various invasive species creates a hostile environment for both native species and grazers.

Resilience management. The resilience and resistance of the invaders create a management road block that is usually financially driven. Many times, once an invasion reaches this point, many land managers have no choice but to learn to utilize what they have rather than to try to treat or improve the site, specifically in relation to cheatgrass control.

Community 4.1
Invaded

Figure 20. Two-years post burn, this bluebunch dominated site has a dense understory of cheatgrass.

Downy Brome, better known as cheatgrass (Bromus tectorum), is able to green up and grow late into the fall and green up early spring before snowmelt. This early and late growth pattern allows cheatgrass to utilize fall and spring resources that are otherwise stored for the cool-season perennial vegetation before the native species can begin to break dormancy. Seeds are able to persist for long periods of time until growing conditions are optimal, allowing growth before most native species. The plant’s ability to grow quickly utilizing minimal available resources and the ability to produce large quantities of seed quickly, and to reproduce in poor conditions are what drives this plant above the natives and many improved varieties of grass. The morphology of the seed allows for easy dispersal and longevity creating a widespread and long-term seed bank. These traits create a management challenge that has not been successfully met at this time. Once this species has a niche on a landscape it is resistant and resilient to change. In this community, with the absence of sagebrush, there may be native species that will persist in small scattered populations or sparsely under the canopy of the cheatgrass. Certain climatic conditions will allow natives to show their resiliency and respond to the available resources (typically mid spring moisture), but are generally unable to out-compete the annual invader, and remain secondary in the community. The ability for cheatgrass to emerge, bolt, produce seed and mature out two to three times within a year utilizes all available soil nutrients and moisture resources. Chemical control is difficult to attain and maintain success without lasting effects on the native grasses in the area. Chlorosis of wheatgrasses, stunted plants, and loss of certain forbs are a few of the residual chemical effects. This generally comes from the chemical composition and its ability to bind to the chemistry or nutrients in the soil inhibiting the uptake by roots. The extensive fine fuels/biomass load created by cheatgrass can increase the fire frequency interval to an annual to five year cycle, preventing sagebrush and other woody species from establishing on the site, and has negative impacts on many of the native herbaceous species in the understory, by increased evaporation and mineralization/vaporization of many of the nutrients rendering the soils nearly sterile. The grazing potential is limited due to the unpalatable and harsh environment that the mature seeds create with their long awns and chaff. If grazed in early spring or late fall some of this can be avoided, but general use through the middle of the growing season is difficult, and defeats the purpose of intensively grazing the location. In smaller invaded sites or under certain conditions, grazing can be used as a tool within the integrated pest management toolbox, but it is not effective alone.

Resilience management. This plant community is resistant to change. Plant diversity is poor. The plant vigor is diminished and replacement capabilities are non-existent due to the loss of cool-season grasses. Plant litter is noticeably more when compared to reference communities in response to the dense duff layer created by Cheatgrass. Soil erosion is generally reduced in response to the litter accumulation; however, the annual nature of this plant accentuates the water flow patterns and pedestalling. Infiltration is reduced and runoff is increased with the loss of perennial vegetation and root depth and density. Overall biotic integrity is lost in this community.

State 5
Altered

Disturbance to these highly erodible soils (whether it was mechanical, cultural, or natural) reduced the resilience or resistance to support native vegetation or the ability to respond to management in the same manner as an undisturbed site. Changes to soil structure and hydrologic processes reduce the stability and ability to recover. Reclamation or restoration of an area is limited or restrictive due to slope, access, and lack of depth to bedrock. These "altered" lands may, after significant inputs and time, resemble the Reference Communities (1.1 or 1.2), but they will not respond or function the same as the Reference State. One catastrophic event or several smaller disturbances can lead to the transition to the Altered State from any identified state within the State-and-Transition Model. The soils have not been altered to the extent that they are outside the site characteristics, but the potential has shifted enough that it will not respond like the Reference State. The time required to allow the redevelopment of structure and the cryptogrammic crust is beyond the natural function of management. The initial flush of vegetation is annual forbs, including mustards, a successional plant community. The site begins its own recovery, but the time required to return to the original conditions (pre-disturbance) can be extensive. The site, however, may become similar in composition to the Reference State.

Characteristics and indicators. The Altered State is characterized by a landscape that has had significant soil disturbance. Early successional plant communities, evidence of mining, or the presence of introduced species (crested wheatgrasses, Russian wildrye, etc.) are indicators of this State.

Resilience management. Stabilization and preservation of as much soil as possible is the mechanism to provide resiliency to this State. The use of mulch or other slope stabilization materials will help in reducing erosional impact and allowing vegetation to establish.

Community 5.1
Disturbed

Disturbed or degraded lands are characterized by alteration of the soils to a degree that the functionality (erosional, depositional, hydrological, or chemical) and potential of the soils has been impacted. Site-specific evaluations need to be completed to determine the level of effect. The method and severity of alternation, as well as the spatial extent of the disturbance will determine vegetation response and management needs. Linear disturbances, such as trails and roads, will hold a different risk than patchwork or polygonal disturbances, such as well-pads or parking areas. Small-scale or isolated disturbances (spot fires, prairie dog town) can be just as significant of a risk as a large-scale disturbance (mine lands). The growth curve of this plant community will vary depending upon the successional or seeded species that are able to establish in an area. For an accurate growth curve, a site-specific species inventory and documentation of the climatic tendencies should be collected.

Resilience management. Rangeland Health Implications/Indicators: This plant community is variable and, depending upon the age of the stand and the stage of successional tendencies, determines how stable (resilient/resistant) the community is. Plant diversity is low for successional communities. This flexibility within the community creates a variable level of biotic integrity. In areas of new or frequent disturbance, annual weedy species or early successional plants will be the dominant cover, providing some diversity, but gives minimal structural cover for wildlife. As the site matures or as the period between disturbances is lengthened, perennial or taller-statured, stronger-rooted species will increase providing protection and help to improve hydrologic processes and stability to allow grasses and shrubs to begin to establish. Soil erosion is dependent on the disturbance regime and the biotic integrity of the community which determines water flow, infiltration, and runoff. Other factors that are influential are surface roughness and brokenness (tire tracks, hoof action, smoothed, denuded surfaces, trails that may concentrate water flow).

Transition T1A
State 1 to 2

Frequent and severe grazing plus no fire (lack of browsing on shrubs) will convert the plant community to the Mixed Shrub/Bare Ground Plant Community. The probability of this occurring is high, especially evident on areas with historically higher precipitation and where drought or heavy browsing does not adversely impact the sagebrush stand.

Constraints to recovery. The lack of a seed bank and the shallow depth to bedrock limits seedling establishment and survival. The unpredictable and variable spring precipitation also limits success of recovery.

Transition T1B
State 1 to 3

Frequent and severe grazing (yearlong grazing) plus wildfire or brush control, will convert the plant community to the Sod-former State. The probability of this occurring is high, especially if the sagebrush stand has been severely affected by drought or heavy use or has been removed altogether.

Constraints to recovery. The dense root mat formed by threadleaf sedge alters the hydrology, effectively removing moisture from the site, limiting the available resources for other native species. The dense sod also limits the available soil space for seedling establishment. Interpspaces between sod patches are prone to erosion and runoff (limited infiltration of moisture).

Restoration pathway R2A
State 2 to 1

Brush management, followed by prescribed grazing, will return this plant community at or near the Reference State. Reseeding after brush management with native species may be necessary to ensure a more rapid transition. If prescribed fire is used as a means to reduce or remove the shrubs, sufficient fine fuels will need to be present. This may require deferment from grazing prior to treatment. Post management is critical to ensure success. This can range from two or more years of rest to partial growing season deferment, depending on the condition of the understory at the time of treatment and the growing conditions following treatment. In the case of an intense wildfire that occurs when desirable plants are not completely dormant, the length of time required to reach the Reference maybe increased and seeding of natives is recommended.

Transition T2A
State 2 to 3

Brush management, or an intense wildfire followed by frequent and severe grazing, will convert the plant community to the Sod-former State.

Constraints to recovery. The dense root mat formed by threadleaf sedge alters the hydrology, effectively removing moisture from the site, limiting the available resources for other native species. The dense sod also limits the available soil space for seedling establishment. Interpspaces between sod patches are prone to erosion and runoff (limited infiltration of moisture). The lack of sagebrush or other shrubs and the loss of snow catch to the system also impacts the recovery. Sagebrush is slow to re establish and with altered hydrology may not recover in this system.

Transition T2B
State 2 to 4

Catastrophic or intense wildfires, prolonged drought with severe use by large herbivores or large scale land disturbance creates an environment ready for Invasion. In areas where invasive species are present, the exposed soil and lack of native vegetation from already stressed communities encourages invasive species to establish as a mono-culture with possibly only small isolated remnants of native species. The canopy of Wyoming big sagebrush is the stabilizer for this community. Once it is removed from a community, it is extremely difficult to re-establish. Wyoming big sagebrush may require 25 years or greater to establish naturally, and in many cases will require outside assistance. The open raw landscape with minimal native species provides the perfect opportunity for invasive species, primarily Cheatgrass, to establish and take over a community. Drought or insects and disease serve to exacerbate the situation.

Constraints to recovery. The lack of other key herbaceous species also is a constraint on this site. The inability, at this time, to eradicate cheatgrass does not allow for a complete recovery of an invaded community.

Transition T3A
State 3 to 4

Drought, or drought with grazing intensity together, weakens a water limited system allowing invasive species the opportunity to take advantage of the limited moisture. Threadleaf sedge has been seen to die back or die out with prolonged drought opening the canopy and the community’s vulnerability to invasive species. Disturbance by mechanical means or human activities that break the root masses or disturb the soil surface open this closed community to potential invasive species, especially when there is a readily available seed source for those invasive species.

Constraints to recovery. The sod of threadleaf sedge will continue to impact the hydrology and competition for limited resources in this community limiting the potential for recovery. The lack of other key herbaceous species also is a constraint on this site. The inability, at this time, to eradicate cheatgrass does not allow for a complete recovery of an invaded community.

Restoration pathway R4A
State 4 to 5

Integrated Pest Management, with Seeding the site to a native mixture - Success is not known to have occurred, and is rated to be low and highly variable for the rate of control of most species. Cheatgrass is one of the most invasive species for many of these sites, although there are other challenges. With intensive weed control and inputs this community can resemble an at-risk community within the reference state, but it is not possible to reach the reference community condition once annuals have established on a site.

Transition T5A
State 5 to 4

Any disturbance that occurs or stress that is placed on the herbaceous cover, weakens the canopy and allows for invasive species to establish if a seed source is present. This State is at high risk of transitioning to an Invaded State. The challenge of successful seedings on a very shallow soils and steep slopes leaves the community vulnerable to invasion. The challenge of eradicating or reducing invasive species such as cheatgrass prevents recovery of most invaded communities without significant inputs for weed control, seeding with long-term grazing management.

Constraints to recovery. The challenge of eradicating or reducing invasive species such as cheatgrass prevents recovery of most invaded communities without significant inputs for weed control, seeding with long-term grazing management.