State 1
Bunchgrass/Sagebrush

The Reference State, State 1, is labeled as the Bunchgrass/Sagebrush State. Wyoming big sagebrush has a foothold in the community but mid-stature bunchgrasses are the dominant contributors to composition.

Characteristics and indicators. This State is characterized by the key species, including 10 percent or less composition by cover of Wyoming big sagebrush, with predominantly needle and thread and Indian ricegrass (30-50 percent composition). Areas of thickspike wheatgrass exist with the other minor components to the overall composition which are prairie Junegrass, bottlebrush squirreltail, sand dropseed, threeawn, blue grama, and threadleaf sedge.

Community 1.1
Needleandthread/Indian Ricegrass Plant Community

Figure 10. Community 1.1 – Reference Site located east central Park county, with needleandthread and Indian Ricegrass.

Community Phase 1.1 is the Reference Plant Community; however, it is declining in occurrence on the landscape. There are several potential factors that are causing this decline, however the change in timing of precipitation and temperatures (spring warmup/fall freeze) or lack of precipitation could be the dominant driving factors for this loss. State 1, including Community Phase 1.1, evolved with grazing by large herbivores. The potential vegetation consists of 70 percent grasses or grass-likes, 20 percent forbs, and 10 percent woody plants. This plant community is found on properly managed landscapes that include grazing or ecosystem-based management tools, with natural disturbance regimes and on areas that receive occasional short periods of rest. Changes in herbivory pressure by sheep and wildlife in the area have allowed Wyoming big sagebrush to become increasingly woody and decadent. This lent to the perception of increased woody canopy; however, the community is still dominated by cool-season perennial grasses. Overall, a stronger presence of short, warm-season grasses (blue grama) has increased across the entire basin, but has remained as a secondary component in this Reference Community. Historically, the Reference State evolved under a low fire frequency, estimated to be 195 to 235 years between burns on the same community patch, and sagebrush has a post-fire recovery timeframe of 50-120 years or more in arid systems (Baker, 2006) and with grazing pressure by large ungulates (elk, bison, deer, or antelope). Needle and thread, Indian ricegrass, and thickspike wheatgrass are the dominant grasses. Other grasses that are common include prairie Junegrass, Sandberg bluegrass, blue grama, threadleaf sedge, and threeawn. Forbs common to this site include fleabanes, fringed sagewort, wild parsley, lemon scurfpea, and scarlet gaura. Wyoming big sagebrush and winterfat are conspicuous components of the community and can make up to 10 percent of the foliar cover. The overstory of sagebrush and understory of grass and forbs provide a diverse plant community overall. The total annual production (air-dry weight) of this community phase is about 400 pounds per acre, but it can range from about 225 lbs./acre in unfavorable years to about 600 lbs./acre in above average years.

Resilience management. Rangeland Health Implications/Indicators: Diversity of the plant species found on this site allows for a high tolerance to drought, allowing persistence in the limiting climatic conditions of the Big Horn Basin. Wyoming big sagebrush in conjunction with the mid-bunchgrasses (needle and thread and Indian ricegrass), rhizomatous species (western wheatgrass and thickspike wheatgrass), and the short-statured bunchgrasses (prairie Junegrass, Sandberg bluegrass, and threeawn) help to provide snow catch, holding moisture to maximize availability during the growing season. The adaptive species in this community respond to timing of precipitation, varying in composition but maintaining cover through a variety of conditions. As an example of this adaptability, needle and thread is dependent upon early spring moisture to perform well. Years with late spring/early summer moisture will produce minimal to no needle and thread but will have an excellent cover of prairie Junegrass. However, a year with late fall moisture and a slow warm up with spring moisture will produce an excellent cover of Sandberg bluegrass but minimal production for prairie Junegrass and needle and thread. The persistence and adaptability from year to year of these species allows for quick recovery once normal precipitation returns. This adaptability or variability in composition is one factor for the natural shift between Phases 1 and 2. Extended periods of drought, changes in land usage, and other natural and human-derived impacts assist with this shift, but the community is not at risk of transitioning into a different state unless a catastrophic impact occurs. This community, as the Reference, is indicative of rangeland health which is based on site and soil stability, watershed function, and biologic integrity.

Community 1.2
Perennial Native Grasses/Sagebrush Plant Community

Figure 13. Reference Community 1.2 - Sandy 5-9” Mesic site within Big Horn Basin.

The secondary phase of the Reference Community (1.2), is captured as the At-Risk Community. Although it is similar with only minor shifts in composition and function, the loss of Indian ricegrass and the increase in woody cover leaves this site at risk of further degradation with continued stress or pressure by herbivory. The community can be found on areas that are within the scope of historic disturbances such as herbivory by large ungulates and sporadic wildfires. Properly managed locations with grazing with periodic short intervals of rest support this plant community and production potential. The vegetation composition is 65 percent grasses or grass-like plants, 10 percent forbs, and 25 percent woody plants. The Reference State is dominated by cool-season mid-statured grasses. The major understory of grasses and grass-like plants includes needle and thread, rhizomatous wheatgrasses, blue grama, threadleaf sedge, prairie Junegrass, and Sandberg bluegrass. The variety of forbs and half-shrubs commonly found include scarlet globemallow, fringed sagewort, lemon scurfpea, sulfur buckwheat, hairy false goldenaster, and spiny phlox. Wyoming big sagebrush can make up 25 percent of the annual production. The overstory of Wyoming big sagebrush and understory of grasses and forbs maintain the diverse structure of the plant community. Blue grama has increased within this community, as has Wyoming big sagebrush, and yucca when present; however, they are not the most prevalent species. The shift in species has an impact on moving or changing the hydrology of the site. Plains pricklypear cactus will also have increased but occurs only in small patches. Indian ricegrass has decreased and may occur in only trace amounts under the sagebrush canopy or within the patches of pricklypear; whereas needle and thread and winterfat have maintained and are a common component in this community. The total annual production (air-dry weight) of this community is about 350 pounds per acre, but it can range from about 190 lbs./acre in unfavorable years to about 580 lbs./acre in above average years.

Resilience management. Rangeland Health Implications/Indicators: This plant community is resistant to change. The herbaceous cover is intact, and plant vigor and replacement capabilities are enough to maintain during periods of moderate grazing pressure with recovery periods; however, species composition can be altered through long-term overgrazing or increased intensity of defoliation. The overall canopy is adequate, but the shift in structure of cover and increase in bare ground opens a niche for weedy species and may intensify the droughty nature of the soils with increased water demands by the woody species as well as shallower-rooted annuals. Bare ground averages 30 to 45 percent, woody coverage has increased (due to reduced herbaceous cover, to an average of 20 to 35 percent cover. Litter overall appears to be similar across this state (State 1); similarly, the biological crust cover does not vary. Water flow patterns and litter movement may be occurring but only on steeper slopes. Incidence of pedestalling is minimal, and soils mostly are stable with only minimum evidence of soil loss. The watershed is functioning, and the biotic community is intact.

Pathway CP 1.1-1.2
Community 1.1 to 1.2

Needleandthread/Indian Ricegrass Plant Community

Perennial Native Grasses/Sagebrush Plant Community

Timing of grazing, drought, and climatic shifts—The Big Horn Basin is known for the significant populations of sheep and the seasonal move to the mountains for summer grazing and back to the basin for winter grazing. Historically, this site was used during the late fall and winter before livestock could be moved on federal summer allotments. The repetitive use of sensitive species will slowly remove them from the system. This impact is one factor that has reduced Indian ricegrass and encouraged Sandberg bluegrass and prairie Junegrass in some areas. Long periods of drought and shifts in spring precipitation patterns have weakened and impacted the productivity and vigor of most species, leaving a drier climate for sensitive species to establish. Although the species of herbivory and timing has changed with the installation of more grazing management, drought and other climatic patterns still pose a continual threat to the integrity of the plant communities.

Context dependence. Shifts in climate may be a major driver for this transition and may be the restriction to recovery in some instances.

Pathway CP 1.2-1.1
Community 1.2 to 1.1

Perennial Native Grasses/Sagebrush Plant Community

Needleandthread/Indian Ricegrass Plant Community

Long-term prescribed grazing, brush management—Integration of a rotational grazing system and brush management, the native bunchgrasses will begin to reestablish in this community. Recovery may take an extended period, estimated at 5 to 10 years before significant change is noticed. Prescribed grazing, especially following sagebrush canopy treatments helps to remove woody debris and exposes a seedbank to encourage the native species. Allowing rest during critical seedling establishment and reducing competition for resources aids the recovery of native species. Hoof action helps to break up duff layers and open the seedbed to allow the desired bunchgrasses (needle and thread, Indian ricegrass) and rhizomatous wheatgrasses, with prairie Junegrass to reestablish or to increase, which drives the recovery to the Reference Community (1.1). This hoof action, along with brush treatment, can be a tool to break up mat-forming species, which addresses the shifting hydrologic cycle and holds the water on-site rather than allowing it to be lost off-site. A long-term management strategy may be required before any trend toward Reference is noticed. The overstory of Wyoming big sagebrush may be the one factor that could require further manipulation to reduce canopy and composition to the 10 percent that is desired.

State 2
Mixed Shrubs/Bare Ground

Persistence of drought or frequent overuse by livestock or wildlife leads to a decline of the herbaceous species, creating the Mixed Shrub and Bare Ground State. This State can be exacerbated by insects and other human disturbances. The total woody canopy cover does not necessarily always increase with this community, but the percentage of composition by cover and production is swayed by the decrease of herbaceous vegetation and the relative stability of woody production, creating the appearance of increased canopy by shrubs.

Characteristics and indicators. The coarse texture of the soils on this site provides the opportunistic shrubs such as shadscale, spiny hopsage, yucca, skunkbush sumac, and four-wing saltbush to establish along with Wyoming big sagebrush. These shrubs provide protection and create a niche for most herbaceous understory to persist and maintain some vigor in difficult conditions. The additional moisture provided by the shade of the canopy as well as protection from grazing benefit most native grasses.

Resilience management. As the herbaceous cover declines and the site continues to weaken, the sagebrush and other shrub cover is susceptible to attack by insects, disease, and general old age that can remove it from the system leaving it at-risk of invasion or transition to a more degraded state. There is a high level of variability of species in this State (State 2, Mixed Shrubs/Bare Ground), that will shift with precipitation patterns or as a response to past management. Only one well-defined community will be provided, with discussion of transitions or variances from this community. The overall droughty nature of coarse textured soils exacerbates the impact of droughty conditions and reduces the resilience and resistance of this site to further shift during extended dry periods. The presence of spiny hopsage and yucca on this site is not frequent, but when it does occur it can easily become prominent, specifically for winter grazing allotments. Yucca’s growth habits produce a more pronounced pedestalling and drift or scour pattern on the landscape than seen with sagebrush. 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 weather conditions. The loose or coarser texture of these soils allows for increased wind scour and drifting or mounding to occur with more open ground between canopy “patches” that further hinders fire movement. Depending upon the prescription of use, trailing and other erosional patterns are highly visible in this State.

Community 2.1
Mixed Shrubs/Bare Ground Plant Community

Figure 16. Sagebrush Dominated Community with minimal coverage in woody canopy gaps.

This plant community is the result of frequent and severe grazing and/or protection from fire. Wyoming big sagebrush dominates this plant community, as the annual production of sagebrush exceeds 25 percent. Wyoming big sagebrush is a significant component of the plant community and the desirable mid-statured cool-season grasses have been greatly reduced. In response to the coarser textured soils, Yucca can be a major component of this community. The dominant grasses are needle and thread, Sandberg bluegrass, prairie Junegrass, and blue grama with dispersed areas of threadleaf sedge. Patches of pricklypear cactus are more noticeable on the landscape, and the amount of bare ground is more prevalent. As compared with the Reference Plant Community 1.1, the annual production is slightly lower. Woody production and cactus maintain production even though herbaceous production has declined. This community is vulnerable to invasive weeds such as cheatgrass, Russian knapweed, or leafy spurge if a seed source is available, leaving it labeled as at-risk of further degradation. The total annual production (air-dry weight) of this state averages 385 pounds per acre, but it can range from 205 lbs./acre in unfavorable years to 560 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. The increased interspaces make this community susceptible to invasive species. 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, vigor is diminished, and replacement capabilities are limited due to the reduced number of mid-statured cool-season grasses. Plant litter is noticeably less when compared to the Reference Plant Community. 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-formers

The dominant sod-forming grass or grass-like that currently exists within this LRU is blue grama; however, there is a limited component of threadleaf sedge. Both are species that persist as a component of the perennial vegetation naturally (in Reference communities) within this ecological site. The general tendency is for these species to increase with prolonged drought or under grazing pressure, becoming dominant.

Characteristics and indicators. This community is characterized by a dominance of blue grama with some threadleaf sedge. Remnants of the other vegetation natural to this site will persist, but is restricted by the dense mats of blue grama.

Resilience management. Together as the dominant species, they alter the hydrology of the site by increasing the surface runoff from the dense shallow root system that inhibits the movement of water through or will direct surface flow around the edge of the “clump,” concentrating flow into channel-like patterns, creating a drier environment for native grass species and forbs to persist.

Community 3.1
Sod-formers/Sagebrush Plant Community

Figure 19. Blue grama dominated community with sagebrush still present.

This plant community is the result of continuous season-long grazing, recurrent over utilization, or prolonged drought, which has adversely affected the perennial grasses and shrub component, in turn encouraging the low-statured, mat-forming (tillering) grasses to expand. The effect of blue grama and threadleaf sedge with their short, dense root structure, is a decrease of water infiltration which increases channelization of runoff between vegetation patches. Decreased infiltration coupled with the lack of structure to hold moisture and compounded by drought will reduce the shrub component further. Dense, interspersed patches of blue grama and threadleaf sedge sod are the major components of this community. Incidental occurrences of other perennial natives occur within the sagebrush canopy or the protective ring of the pricklypear cactus clumps. Overall, Wyoming big sagebrush has been reduced in vigor and abundance across this community phase, but it persists on the landscape (average of 5-10 percent canopy cover). When compared to the Reference Plant Communities 1.1 and 1.2, blue grama has increased significantly, making up 30 to 60 percent of the canopy. Pricklypear cactus is prevalent on the site, and other cool-season mid-statured grasses, perennial forbs, and most shrubs have been greatly reduced. Production has significantly decreased, and bare ground may not vary or will increase (longer extents of bare ground between densely vegetated areas). The total annual production (air-dry weight) of this community phase is about 150 pounds per acre, but it can range from about 60 lbs./acre in unfavorable years to about 300 lbs./acre in above average years. The higher productivity generally is in response to Wyoming big sagebrush production on the site. Rubber rabbitbrush and other woody species are present as well (5-10 percent), influencing overall production.

Resilience management. Rangeland Health Implications/Indicators: This community is at-risk of transitioning to a sod-bound community with no woody vegetation. The short-statured tillering plants are resistant to change. No added effect to the plant composition or structure is apparent with continued overuse or with the application of non-use. The shrub component will degrade and eventually will be removed from the plant community under either scenario. The biotic integrity of this community phase is not functional and plant diversity is extremely low. The plant vigor is weakened, and replacement capabilities are limited due to the reduced number of mid-statured cool-season bunchgrasses. This sod-bound plant community is resistant to water infiltration. While the sod protects the rooted area, edge areas are affected by excessive runoff that can cause rills and gully erosion. Water flow patterns are obvious in areas of bare ground, and pedestalling is prominent 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. This community can improve with intensive management requiring mechanical manipulation. However, once the sagebrush component has been lost, recovery or transition is not as feasible. The potential to recover compared to the potential to shift into Community Phase 3.2 (stable and most degraded) creates the at-risk label. Drought stress will create a die off or die-back of both blue grama and threadleaf sedge. During extended periods of drought, large areas of die-back leaves the area sensitive to hoof action. When the blue grama plant dies, it tends to die from the center out, but will remain intact until disturbed (trampling, vehicle traffic, ground disturbances). Once disturbed, the plants quickly degrade, leaving the surface vulnerable to erosion.

Community 3.2
Sod-formers/Cactus Plant Community

Figure 22. Blue grama Community with Cactus in a good year for Sandberg bluegrass.

Further degradation of the Sod/Sagebrush Community Phase (3.1) to the Sod/Cactus Community Phase (3.2) occurs relatively easily under long-term drought or continued pressure on the remaining shrubs. This phase transition could be viewed as successional phases. A dense sod of blue grama with threadleaf sedge intermixed, is dominant with increasing pricklypear cactus in the community. Cactus density has the potential to increase to a level that inhibits the ability for livestock to move through or graze the available forage. Wyoming big sagebrush has been generally removed from the community with only isolated occurrences. Rubber rabbitbrush is significantly reduced but may persist on the landscape. The dense mats of roots of blue grama and threadleaf sedge and the aggressive stolon of plains pricklypear cactus can tolerate high levels of use and will persist as other native species are removed from the community, including Wyoming big sagebrush. This decline creates a Sod/Cactus Community that is resistant to change with management. When compared to the Reference State (1.1 and 1.2), blue grama and plains pricklypear cactus have increased. All cool-season mid-statured grasses, forbs, and most shrubs have been greatly reduced or removed. The dense and frequent clumps of cactus do offer a niche for some native cool-season grasses to persist in the community but suppressed in expression. Production is greatly reduced from Reference, but minimal difference in production is seen between phase 3.1 and 3.2. The ability of low-statured sod-formers to respond to the amount and timing of precipitation is not as significant as other mid-statured cool-season grasses, such as needle and thread and Sandberg bluegrass; however, marked swing in average production between wet and dry years is seen. The production of substantial inflorescence and culm growth is a more prominent response for these short-statured grasses. Production is provided as an average or mean number and is not intended to cover the full range of production potential for this community. Total average annual production is 175 pounds per acre, but it can range from 75 lbs./acre in unfavorable years to 325 lbs./acre in above average years.

Resilience management. Rangeland Health Implications/Indicators: This community 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 the Sod-Formers State is not functional, plant diversity is extremely low, and vigor is significantly weakened, and replacement capabilities are limited due to the reduced number of cool-season grasses. The dense root mat of this community is resistant to water infiltration, and 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 downslope. The watershed may or may not be functioning, as runoff may affect adjoining sites. The added competition and rooting nature of cactus allows it to become significant or dominant on the site. Although not documented in this LRU at this time, it has been noted in other areas of Wyoming, that pricklypear cactus can form in dense patches that inhibit animal movement through the area, preventing the use for grazing and hindering wildlife movement and use as well.

Pathway CP 3.1-3.2
Community 3.1 to 3.2

Sod-formers/Sagebrush Plant Community

Sod-formers/Cactus Plant Community

Intensive brush management, frequent or severe grazing, and drought—The altered hydrology of this community has created a drier soil environment and reduced seedling establishment of native grasses and shrubs. Once sagebrush is removed from this community by intense grazing pressure, drought and insect damage, or by wild or prescribed fire, the community will phase into a Sod/Cactus Community. The Wyoming big sagebrush component of this community is the at-risk species and is replaced in dominance by pricklypear cactus. Drought alone, or with continuous grazing pressure, will create a sagebrush canopy that is decadent and dying. The sod-dominated community reduces the ability for sagebrush to propagate, also leading to a recession of sagebrush. The influences of fire are rare and generally have little influence on this community due to the lack of fine fuels and canopy cover to carry it; but in rare circumstances, isolated areas may burn within the shrub canopy. In some cases, rubber rabbitbrush will persist or increase slightly on a site as sagebrush diminishes. It is also noted that with periods of drought there is a noted decrease in the health and vigor of threadleaf sedge and blue grama. The dense root structure of the sod-former is reduced and easily disturbed with hoof action.

State 4
Invaded

Wyoming rangelands, much like the neighboring states, has quickly fallen victim to the aggressive invasion of cheatgrass, also called downy brome (Bromus tectorum). The rapid development of an extensive seedbank and duff layer forms with the potential for multiple growth cycles throughout a year. The advantageous ability of cheatgrass to persist through the winter under a blanket of snow and sprout early makes it difficult for natives to outcompete it for limited resources. Shifts in climatic patterns, changes in management, and exposure to human activity are a few of the explanations for the current flush and rapid expansion across the western United States. Although cheatgrass is the most prevalent large-scale threat for rangeland managers, a variety of knapweeds (spotted, Russian, etc.), in combination with other aggressive invaders such as whitetop (hoary cress), black henbane, field bindweed, and leafy spurge are increasing in density and frequency, producing their own set of challenging management issues. As more species are found or as other species become more prevalent on a large scale, the community dynamics in this state will shift in response to the concerns of the identified species.

Characteristics and indicators. The Invaded State is characterized by the presence and eventual dominance of invasive and non-native species. The open canopy of the arid native community combined with extended periods of drought alone or in combination with overutilization, insect damage, or wildfire, has weakened the native composition, thus allowing invasion.

Resilience management. The competitive nature of annuals and other invasive species creates a complex environment that inhibits control and makes it implausible to attain complete eradication once an invasive species has established on the landscape.

Community 4.1
Native/Invasive/Sagebrush Plant Community

Figure 25. Native grasses and sagebrush an understory of cheatgrass.

The Perennial Grasses/Invasive Species/Wyoming Big Sagebrush Community Phase has maintained a representative composition of native perennial grasses and forbs that are key to this ecological site with the accompanying Wyoming big sagebrush component. Although this community phase is very vulnerable of becoming an invader-driven system, if the invader can be maintained at 5 to 10 percent composition, the probability of the community to persist and possibly improve is retained. However, extent of improvement and exorbitant costs and labor required limit the economic feasibility. Further degradation of this site increases the cost and reduces feasibility of restoring a desired community, which makes this community phase the At-Risk Community. This community phase is characterized by a marked composition of invasive species (5 percent or greater) on the landscape; with a wide-scale distribution, not one isolated patch in an isolated portion of the landscape). The composition still includes a significant native population, and litter has not become inhibiting at this phase in degradation. Production yields of the perennial grasses and forbs are slightly reduced but the total production will maintain or may be slightly elevated due to the overall biomass and expanded growth potential of many of the annual or invasive species. A specific production range is not provided due to the variability of composition that will affect overall production.

Resilience management. Rangeland Health Implications/Indicators: This plant community’s susceptibility to fire increases as fine fuels increase with the added biomass and litter produced by invaders (most specific to cheatgrass). Plant diversity is maintained by the remnants of native perennial grasses and shrubs. The plant vigor is diminished, and replacement capabilities are limited due to the reduced cover of cool-season grasses. Limited resources (moisture and nutrients) also inhibits native vigor and persistence in the community. Litter cover and soil erosion for this phase has had minimal to no noticeable change in this community phase. Water flow patterns and pedestalling may be slightly more visible in response to the loss of some native cover. Infiltration is unaltered or slightly reduced; however, as the duff layer or litter builds infiltration and runoff will increase.

Community 4.2
Invasive/Sagebrush Plant Community

Community Phase 4.2 is characterized by the existence of sagebrush with only remnant populations of native species and a dominance of invasive species. As the native populations of perennial grasses and forbs are removed through severe use or disturbance, the site becomes invader-driven. Continued environmental- or management-derived impacts to the shrub component places this community at risk of crossing a threshold. Wyoming big sagebrush can compete and maintain a strong community under a heavy infestation level of most invasive species, unless fire or similar disturbance removes the woody cover. The canopy of the sagebrush serves as a protective niche in the system for native grasses and forbs, allowing remnant populations to persist. But the system is low in resistance and even lower in resilience. The fine fuels or biomass produced by cheatgrass and others raises a significant threat of fire and increases the potential frequency of occurrence and intensity. Strategies to control or manage for invasive species, namely cheatgrass, are the subject of research across the western United States. High-intensity grazing with chemical control and the use of biological agents are techniques that have been given trials with varying levels of success. The key management strategies must be to maintain the remnant populations of native grasses and to reduce the risk of fire to allow the persistence of Wyoming big sagebrush. This will maintain the reduced biotic integrity (maintaining species richness, providing structure and a range of growth traits allowing adaptability of the site to varying climatic swings) and help to support the hydrologic function (providing snow catchment, and shade to allow a slow release of winter precipitation during spring melt, which gives a longer moist season for optimal growth of native species). Each location must be addressed individually to determine the best management strategies to utilize the native species present in the system and to determine the limitations of the resources.

Resilience management. Rangeland Health Implications/Indicators: This plant community is resistant to change in relation to returning to a native dominant system, but as the pressure from invasive species continues, it loses its resistance as it shifts to an invader-only community. These areas may be more prone to fire as fine fuels are more available with increased biomass and plant density as the annual invaders fill interspaces. Plant diversity is poor. The plant vigor is diminished, and adaptability and replacement capabilities are limited due to the reduced number of cool-season grasses. Plant litter is noticeably more when compared to the Reference communities due to the potential biomass produced by the invasive species (species-dependent). Soil erosion is variable depending upon the species of invasion and the litter accumulation thus associated. The variability of the water flow and pedestalling, as well as infiltration and runoff, is determined again by the species that establishes on this site.

Community 4.3
Invasive Plant Community

Downy brome, better known as cheatgrass (Bromus tectorum), can green-up and grow late into the fall and green-up early spring before snowmelt; this growth pattern allows cheatgrass to utilize fall and spring resources that are otherwise stored for the cool-season native vegetation before they can begin to break dormancy. The morphology of the seed allows for easy dispersal and longevity, creating a widespread and long-term seed bank. Seeds can persist for long periods of time until growing conditions are optimal, allowing growth before most native species. The ability of the plant to grow quickly, utilizing available resources and producing large quantities of seed rapidly, and to reproduce in poor conditions are what drives cheatgrass above the natives and many improved varieties of grass; as well as creates 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. The absence of sagebrush in this community restricts the potential for native herbaceous species, but some will persist in small scattered populations or sparsely under the canopy of cheatgrass. When climatic conditions are optimal, these resilient native species will respond to the available resources (typically mid-spring moisture). They are not able to out-compete invasive species long-term, so are restricted to a minor composition in the community. The ability for cheatgrass to emerge, bolt, produce seed, and mature 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: plateauing is what has been observed in this region. 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 risk, frequency and intensity of wildfires increase with the increasing fine fuels (biomass load) created by cheatgrass. The fire frequency interval has been noted to shift to a possible five-year cycle, preventing sagebrush and other woody species from establishing on the site. Negative impacts on many of the native herbaceous species in the understory are intensified by increased evaporation and mineralization or 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. Rangeland Health Implications/Indicators: 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 generally is reduced in response to the litter accumulation. Infiltration and runoff are variable due to the loss of perennial vegetation, but with the potential increase in root density. Overall biotic integrity is lost in this community.

Pathway CP 4.1-4.2
Community 4.1 to 4.2

Frequent or severe grazing, wildfire, and drought—Drought, wildfire, or other climatic stresses on the system will continue to hinder the native species, reducing their ability to maintain their footprint in the plant community. Wildfire is still rare at this phase, but there is an ever-increasing risk with increasing invasive species cover. Continued stress of frequent or severe grazing pressure from wildlife and livestock can reduce the native composition to an unviable or unsustainable population and allow the invasive species to dominate. Wildlife and livestock will utilize cheatgrass and other invasive species but tends to be during initial spring green-up while natives are still dormant or in the fall after the natives have dried down, but invasive species have a secondary flush of growth. This is more typical in species such as knapweeds, whitetop, and specifically cheatgrass (downy brome).

Pathway CP 4.1-4.3
Community 4.1 to 4.3

Extended periods of frequent or severe grazing and/or drought, or wildfire—A major disturbance that removes sagebrush as well as other native herbaceous species leaves the community vulnerable to invasive species. With the increase in fine fuels created by cheatgrass and other invasive species, the wildlife risk of this community rises and can further transition this site to an invasive-dominated community (near-monoculture). Continued stress of drought or frequent and severe grazing can also further degrade this community, allowing for a complete invasion.

Context dependence. The transition from a sagebrush and native grasses driven state to a invader driven state may occur over a period of time, but generally this transition is related to a catastrophic type event. These events may include a wildfire, mechanical treatment failure, or construction type activities.

Pathway CP 4.2-4.1
Community 4.2 to 4.1

Integrated pest management and weed control and long-term prescribed grazing—Control of invasive species and managing grazing to allow use of the invasive species with minimal impact to the native population, will allow the community to regain or maintain potential. But currently, it is not possible to eradicate the invasive species, and sustained control requires intensive inputs over the course of several years. To maintain the system with no further degradation requires a dual approach with both long-term prescribed grazing and intensive weed management (integrated pest management). No one single practice can sustain this phase, as it requires intensive management to prevent the transition to Community Phase 4.3 – Invaders (Annuals), and to encourage the recovery of native species.

Context dependence. Extent of control and ability of the community to recover (native grasses primarily) is dependent on climatic conditions and the invasive species that has established in the community.

Pathway CP 4.2-4.3
Community 4.2 to 4.3

Catastrophic or extreme grazing and/or drought events, or wildfire—The transition to Community Phase 4.3 can occur with continued extensive use and drought. However, the complete loss of sagebrush generally occurs under a major disturbance (fire, mechanical alteration, chemical means) and establishment of invasive species will become a near-monoculture.

State 5
Altered

The arid nature of this region has played a major role in the development and transitions in land use over time. Early settlers worked to farm any land that was accessible by water (canal systems) and equipment. Many of these small areas were later abandoned and left to return to rangeland. Other landscapes were treated with a variety of prescriptions to manage or eradicate sagebrush. Tillage of the soil, changes in hydrology caused by the loss of vegetative structure, constant natural climatic fluctuations, and advancements in seed sources has led to the creation of a site description for the Altered State. The disturbed or degraded state could be drafted as a stand-alone box within the State-and-Transition Model diagram. No matter how a location is classified, once the site has experienced an event that has altered the soil properties (erosional, depositional, hydrological, or chemical), the site potential is altered. To consider this as an alternate ecological site would not be unreasonable. In some cases (site by site consideration), recorrelation of a location may be the best solution. In many cases, however, the soils have not been altered out of the current site characteristics, but the potential has shifted enough that it is no longer truly comparable to the Reference State (State 1).

Characteristics and indicators. Mechanical, cultural, or natural disturbance to soils resulting in an alteration of structure, hydrologic function, and possibly stability prevent a site from supporting the native vegetation or responding to management in the same way as an undisturbed site. Reclamation or restoration of an area will not replace the original function and factors that made the original location respond as it did. Therefore, 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 as the Reference Community.

Resilience management. The species selection, extent or occurrence of tillage, and the resulting loss of structure, moisture, biotic degradation, changes in infiltration and water-holding capacity, and change in permeability are all factors that affect a planted site. The time required and feasibility for the redevelopment of soil, as well as variability in plant establishment and climatic conditions determine the successional path after a disturbance event. Kochia, Russian thistle, and mustards are the typical primary successional species in this LRU. Although they provide organic material, nutrient flow and erosional protection, they lack the structure and root system to fully stabilize the site. With time, the site may become similar in composition to Reference, but the integrity of the soil is altered, changing community potential. To capture the dynamics of this process, an Altered State was added to document these communities that exist on the landscape.

Community 5.1
Disturbed/Degraded Plant Community

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. 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). Site-specific evaluations need to be completed to determine the level of effect. Variability of the plant composition within this community prohibits the selection of one specific growth curve. Growth curves for seeded locations will vary, especially with the use of non-native or cultivated species. In the case of an early successional community or naturally recovering system, the growth curve may resemble the pre-disturbed community. For a more accurate growth curve, a site-specific species inventory and documentation of the climatic tendencies should be collected.

Resilience management. Rangeland Health Implications/Indicators: The plant community is variable and, depending upon the age of the stand and the stage of successional tendencies of the location, will determine how stable (resilient/resistant) the community is. Plant diversity of these successional communities generally is strong but is usually lacking in the structural groups that are desired on the site. In areas of new or frequent disturbance, annual weedy species or early successional plants will be the dominant cover, providing a strong diversity, but this community has minimal structural cover for some wildlife. As the site matures or as the period between disturbances is lengthened, perennial or taller-statured, stronger-rooted species will increase providing protection, improves hydrologic processes, and allows establishment of grasses, forbs, and shrubs. This flexibility within the community creates a variable level of biotic integrity. Soil erosion is dependent upon the disturbance regime and the biotic integrity of the community. The variability of the community also affects water flow, infiltration, and runoff, which in turn effects the potential risk for erosion and pedestalling. Other factors that are more prevalent or influential for these sites are surface roughness and brokenness (tire tracks, hoof action, smoothed, denuded surfaces, trails that may focus the water).

Community 5.2
Restored/Reclaimed Plant Community

Improvements in techniques and technology for reclamation practices over the last several decades have altered the success and stability of reclaiming a site. Crested wheatgrass was a species used frequently for reclamation throughout Wyoming. These stands are still present today, and generally are stable as a monoculture until a disturbance creates a niche for other species to establish. In limited areas, there are indications that crested wheatgrass is creeping out into native communities as readily as native species are moving into the crested wheatgrass stands. With time, species such as Russian wildrye and varieties of rhizomatous and bunch-wheatgrasses were added with crested wheatgrass to provide a diversity of longevity and initial establishment. Variability in timing and amount of precipitation in this LRU limits the success of range plantings. However, limited success has been documented along pipeline corridors, well or pad sites, and along transportation corridors. Current interpretations of reclaimed or restored refers to the establishment of native species in a composition as close to a natural (pre-disturbance) plant community as possible. This excludes the use of non-native species. Although native species are used in reclamation, these plantings will not replicate the Reference Community in response to management due to the change in soil dynamics with mechanical disturbance (seedbed preparation and seeding), but they may be similar. The use of native cultivars allows for an ecological response that resembles pre-disturbance closer than a non-native community. The growth curve of this plant community will vary depending upon the species that are selected for the reclamation seed mix. For a more accurate growth curve the species used, and the climatic tendencies of the area specifically must be considered.

Resilience management. Rangeland Health Implications/Indicators: The resistance to change and resiliency of a plant community is determined by the specific seeding mixtures. Success in establishment of this mixture and the conditions of the site will determine the ability to resist against weed infestations as well as the potential for erosion. Many of the seeded communities are diversity-poor. Historic seedings of one or two species limited the resiliency of a site but provided a substantial benefit. The current seeding standards have helped improve these benefits, but are limited by the seed sources available, the ability to prepare and seed the location, and the economics of the planting. Many seeded sites may be prone to fire because of the increased production as they mature (more biomass and possibly more litter), providing abundant fine fuels to carry a fire. Soil erosion is variable depending upon the establishment of the seeding, how it is seeded, and mechanical procedures put in place. The variability of the water flow and pedestalling as well as infiltration and runoff is determined again by the species that comprise the community and the method of seeding (site preparation and seeding practice).

Pathway CP 5.1-5.2
Community 5.1 to 5.2

Seeding, brush management, integrated pest management, prescribed grazing management—Restoration or reclamation of a site to an intended purpose can be achieved with proper mechanical improvements and follow-up maintenance. However, climatic limitations and quality of preparation will determine the success of plantings. Depending upon the location, plantings are slow to establish and risk of (re)invasion by undesirable species creates a moderately low potential for success. Proper preparation, careful timing, and integrated pest management becomes crucial to allow seeding. Brush management may be required in some disturbed communities to open areas that can readily be seeded.

Context dependence. The type of disturbance that led to the shift from a previous state to this state will determine the further mechanisms required to restore or reclaim this particular community. The successional stage and the species that are establishing will determine the type of land manipulations needed.

Pathway CP 5.2-5.1
Community 5.2 to 5.1

No use, no fire, long-term prescribed grazing, frequent or severe grazing—Decline in plant vigor and health with lack of use or continuous or severe stress allows for a corresponding shift in composition. The seeded plant community and the altered soil properties from seedbed preparation of general disturbances restricts the responses to management from what would be expected under natural conditions. Monitoring and range trend over time helps to determine if a location is degrading or adjusting with the climatic variables of the site. The initial establishment phase of a reclaimed site is crucial to determine success, but at any stage of a seeding, degradation or further disturbance can occur, forcing the site to phase back to a degraded or disturbed community.

Context dependence. The plant species that established during the restoration/reclamation process, the mechanical means of completing this process, and environmental factors all have a major influence of how this community will or may transition back to.

Transition T 1-2
State 1 to 2

Frequent and severe grazing (year-long) or drought with the absence of brush management or wildfire—The conversion to a Wyoming Big Sagebrush/Bare Ground plant community is a response to extended periods of stress, both climate- and human-induced. Frequent or high-intensity herbivory with minimal to no recovery period weakens the ability for the grasses to persist, especially during prolonged drought. With the weakened herbaceous cover, the composition will shift to predominantly Wyoming big sagebrush. Over time sagebrush composition will increase inhibiting the recovery. With added climatic stress, species diversity and productivity are lost, and the community crosses into the Sagebrush/Bare Ground State. An illusion of crossing the threshold to State 2 is created in extended periods of significant fluctuation in precipitation patterns affecting production of prominent plants within this system. The loss of species diversity and increased bare ground over a period of years, along with lack of litter are the indicators that a true transition has occurred. It is important to recognize that woody cover is a factor of the number of plants as well as canopy cover. In some instances, the number of actual sagebrush plants may not increase to cause this shift, but the change in composition or vigor of the wood canopy, as well as the loss of herbaceous canopy, creates the perception of an increased number of plants when it is the ratio, size, and age that is more likely to shift.

Constraints to recovery. Having sufficient key species and cooperation of precipitation and rest from use to allow the native bunchgrasses to re-establish within the interspaces of sagebrush is the main constraint to recovery. Being able to thin while maintaining some woody cover may also be challenging for the recovery process.

Transition T 1-3
State 1 to 3

Frequent grazing (year-long), brush management, or fire with drought—Severe and frequent grazing reduces vigor and presence of key species, mainly needle and thread and Indian ricegrass, and short-statured grasses become dominant. Animal disturbance (hoof impact) and continuous use reduces the bunchgrass component by allowing repeated defoliation of the desirable species and damage to the structure of the plant. These impacts reduce recovery potential and ground cover for insulation and snow catch; weakening and, over time, removing select species. The open canopy and hoof impact encourage species that are tolerant to trampling and short bursts of spring and summer precipitation. These species generally are tillering, mat- or sod-forming species such as blue grama and threadleaf sedge. Prolonged drought stresses the plants and opens the canopy, allowing sod-formers to fill in the interspaces. The shallow, dense root mats will continue to spread over time. The added removal of sagebrush with animal impacts or with fire or brush management may open the canopy more and aid in establishment. Season of use and intensity of grazing (time and timing) are triggers that can reduce the risk of transitioning, or, if done improperly, can force the transition to occur rapidly. The increase in blue grama adds an element of midsummer growth that extends the “green” grazing window. However, adequate amounts and timing of moisture must occur to allow sufficient growth to prevent overuse of the cool-season species.

Constraints to recovery. The ability to weaken or break up the sod-forming species and the lack of remaining native (key) bunchgrasses are the main constraints to recovery for this community.

Context dependence. The time lapse for the occurrence of this state is varied. It is a transition that takes or may take a significant time frame (over ten years) to occur. Recovery may be able to be achieved; but at this time no proof of recovery, without mechanical interference, has been achieved/documented within a management time frame (25 years).

Restoration pathway R 2-1
State 2 to 1

Prescribed grazing with brush management or wildfire—Thinning or patch treatments for sagebrush allow native herbaceous cover to respond to improved moisture and sunlight followed by prescribed grazing to prevent will help this community recover. Treatment will vary depending upon the existing composition of grasses remaining and the potential threats to the location. Removal or thinning of the sagebrush within this community will help to reduce competition, encouraging grasses and forb recovery if the disturbance or overuse (recreational or grazing pressure) is reduced. Drought may prolong the time required for recovery. Mowing or mulching sagebrush trials have shown a strong response by grasses with little to no recovery time post-treatment. The resulting community with these treatments is driven by the dominant species within the community pre-treatment or climatic and treatment conditions during and following may sway the community. It is crucial to investigate the immediate and surrounding area around treatment sites to ensure no invasive species (cheatgrass) are present before treatment type is decided and then applied. The arid climate and lack of fine fuels limits the feasibility of fire as a brush management tool in this system.

Transition T 2-3
State 2 to 3

Drought, Disease or Insect Damage, Over-use, or Fire - Sod-forming species such as blue grama and threadleaf sedge can tolerate high levels of use and will maintain as other native species decline. Hoof action or compaction inhibits more desirable native species, allowing the sod-formers to become dominant on the landscape. This decline creates a sagebrush/sod community that is resistant to change with management. Impacts to sagebrush by disease or insect damage, as well as drought or herbivory, will shift this to the secondary community phase with cactus as a subdominant cover with blue grama.

Constraints to recovery. The hydrologic shift caused by blue grama and the tolerance and resiliency of this species limits the ability to weaken/reduce its foothold in the community enough to encourage the mid-stature bunchgrasses key to this site.

Transition T 2-4
State 2 to 4

Fire (wild), Frequent or Severe Grazing, Drought with Insect Damage/Brush Management – Throughout most of this LRU there is a seed source present for cheatgrass, knapweed, and other invasive species. Stress to the native community from fire, drought, disease/insect damage to sagebrush, or ground/soil disturbance including impacts by grazing large herbivores or recreational uses; opens the canopy and exposes the soil, creating a niche for undesirable and invasive species to establish. Early detection and rapid response provides a chance to prevent a full-scale invasion, but if left untreated, infestations can establish rapidly and spread with one growing season. The population soon grows exponentially as further stress or disturbance occurs. In some cases, once the invasive species are established, they can create their own habitat; this reduces the competitive ability of native species. The open canopy of the Sagebrush/Bare Ground State is vulnerable to invasive species without further influence. With continued over-use, drought, or insect damage/disease, the invasive species will establish and quickly dominate a location. The threshold species in this system is Wyoming big sagebrush, which protects the remnants of the perennial native grasses, allowing them to persist on the landscape.

Constraints to recovery. The lack of sufficient key native species and the inability to eradicate or sufficiently control invasive species are the main constraints to recovery for this state.

Context dependence. Extent of the transition for the sagebrush/bare ground state to the invaded state will determine the severity of the recovery constraints. The loss of sagebrush from this state will further limit/remove any ability of this state to recover back to any previous state.

Transition T 3-4
State 3 to 4

Frequent and severe grazing, drought, or disturbance with a seed source present—Increased interspatial gaps in these communities leaves exposed soil that is vulnerable to invasion by undesirable species. Increased pressure from overuse and drought work to weaken the sod or mat-like community, exposing soil further to annuals and other invaders, such as cheatgrass and knapweeds. The aggressive nature and altered hydrology of these sites do restrict weed invasion. But if a seed source is available, ground disturbance by herbivores or man-induced, allows invasive species to find a way into the community. Once established in the community, it may not be feasible to completely remove eradicate the invasive species. Once the invasive species have become prevalent on the landscape (less than 5 percent composition), the community crosses the threshold into the Invaded/Sagebrush State (State 4).

Constraints to recovery. The lack of ability to eradicate or remove invasive species from the community at this time is the constraint to any recover from the invader driven state.

Context dependence. Substantial evidence that a blue grama dominated community has shifted to a invade/sagebrush or invaded community has not been gathered. It has been documented where a significant population of invasive species (ex: cheatgrass) has established within the inter-spaces of the blue grama sod.

Restoration pathway R 4-5
State 4 to 5

Integrated pest management with seeding—Integrated pest management with intense weed control after and possibly before seedbed preparation will be necessary to overcome a severe weed infestation. Working the soil and preparing a seedbed at a location and using improved varieties, native seed, or, in some cases, an introduced species suited for the intended land use may be the only way to overcome some invasive species. Success of reestablishing a native or desired plant community on a large scale is not documented. Small-scale attempts are rated to be low and highly variable for the rate of control of most species. Seedings can be designed to bring this community that is like an at-risk community within the Reference State, but that it is not possible to reach the Reference Community (1.1) once annuals have established on a site. The limited success of seedings, lack of seed sources for all native species, the possible need to mechanically prepare a seedbed, as well as alternation of soil stability and hydrologic functions inhibit a true Reference restoration for this site. The alteration of the soils, the change in the plant community, and the risk of reinvasion of the site inhibits its ability to react the same to management and environmental changes as a truly native community and so would enter an Altered State.

Context dependence. Species of concern (invasion) will be the determining factor to what processes will need to occur to allow an invaded community to be restored/reclaimed.

Transition T 5-4
State 5 to 4

No use, fire (wild or prescribed), frequent or severe grazing, drought with seed source present—Lack of management to prevent a repeat of a specific disturbance or the absence of use following the reclamation or restoration process will cause the community to revert or transition to an invaded state. Wildfire, prescribed burning, drought, or frequent and severe use by large herbivores can be disturbances that either opens the canopy or introduces the species to the location. Extended periods of non-use create a decadent community with a large proportion of dead growth persisting around the crown of the plants, reducing vigor and production. As the plants begin to recede, the community becomes vulnerable to weed invasions. Frequent or severe grazing, drought, or fire can open the canopy to and assist with the incorporation of seed sources encouraging an invasion as well. This invasion triggers the transition to an Invaded State.

Constraints to recovery. The species of invasion is the major constraint to recovery. Eradication has been unsuccessful for most of the major species affecting these communities on a large scale.