State 1
Bunchgrass/Sagebrush

The reference state (State 1) for the Sandy ecological site is dominated by mid-stature, cool-season bunchgrasses. This state persisted under grazing by large ungulates and was a resource for forage and habitat for a variety of wildlife.

Characteristics and indicators. The Bunchgrass/Sagebrush State (State 1Reference) is characterized by the prominent cover of needle and thread (15-30 percent composition) and Indian ricegrass. Rhizomatous wheatgrasses and prairie Junegrass are common, with 10 percent or less cover of Wyoming big sagebrush. Minor components to the overall composition is made up of Sandberg bluegrass, bottlebrush squirreltail, sand dropseed, threeawn, blue grama, and threadleaf sedge.

Resilience management. Prescribed grazing or managed use to provide forage removal and to help incorporate litter helps for this suit of communities to persist on the landscape and to maintain vigor.

Community 1.1
Needleandthread/Indian Ricegrass Plant Community

This community (1.1) is captured as the Refere nce Plant Community; however, it is declining in occurrence on the landscape. Change or shifts in timing of precipitation, temperature shifts (spring warm-up or fall freeze), or lack of precipitation could be the dominant driving factors for this occurrence. This state evolved with grazing by large herbivores. The potential vegetation cover is about 70 percent grasses or grass-like plants, 20 percent forbs, and 10 percent woody plants. Dominant grasses include needle and thread, Indian ricegrass, prairie Junegrass, and rhizomatous wheatgrasses. Grasses and grass-like species of secondary importance include Sandberg bluegrass, sand dropseed, threeawn, blue grama, and threadleaf sedge. A variety of forbs are found in this community including fleabanes, wild parsley, lemon scurfpea, and scarlet gaura. Wyoming big sagebrush, fringed sagewort, and winterfat are conspicuous components of the community, and can make up to 10 percent of the annual production. The total annual production (air-dry weight) of this community phase is about 500 lbs./acre, but it can range from about 375 lbs./acre in unfavorable years to about 675 lbs./acre in above-average years. This plant community can be found on areas that are properly managed with grazing or other means of defoliation, and on areas receiving occasional short periods of rest. Historically, the Reference State evolved with grazing pressure by large ungulates (elk, bison, deer, and antelope); as well as under a low fire frequency (estimated to be 195 to 235 years between burns on the same community patch; sagebrush has a post fire recover timeframe of 50-120 years or more in arid systems. Baker, 2006).

Resilience management. Rangeland Health Implications/Indicators: Species diversity of this community provides a high tolerance to drought, allowing persistence in the limiting climatic conditions of the Big Horn Basin. The structural diversity of Wyoming big sagebrush in conjunction with the mid-statured 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) helps to provide snow catch and shade, to capture and hold moisture in order to maximize availability during the growing season. This key to the hydrologic function as well as the adaptability of the community to the variability in timing of precipitation helps to provide cover, through a variety of conditions. 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. Whereas 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 natural variability will cause the transition between phase 1.1 and 1.2, but is not at risk of transitioning into a different state unless a significant (catastrophic) impact occurs. Extended periods of drought, use changes, and other natural and human-derived impacts further force this change. This community, as 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

The secondary community phase (1.2) of the Reference State 1, is characterized by the loss of Indian ricegrass and the increase in composition by weight of Wyoming big sagebrush. Otherwise, the shift in in species composition and function is minor. The community can be found on areas that are within the scope of historic disturbances but have been impacted by a shift in climate or management, stability of the site and production potential. The vegetation composition is 65 percent grasses or grass-like plants, 10 percent forbs, and 25 percent woody plants. This community is still dominated by cool-season mid-statured grasses. The major understory of grasses and grass-like plants includes needle and thread, prairie Junegrass, rhizomatous wheatgrasses, threadleaf sedge, blue grama, and Sandberg bluegrass. The variety of forbs and half-shrubs commonly found include scarlet globemallow, lemon scurfpea, scarlet gaura, 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 provide a diverse plant community. Threadleaf sedge and blue grama have increased within this community; however, they are not the most prevalent species, but they have an impact on moving or changing the hydrology of the site. Wyoming big sagebrush and yucca, when present, have increased in composition by weight, but that does not correlate to a composition by cover. 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; needle and thread and winterfat have remained as a common component in this community. The total annual production (air-dry weight) of this community is about 525 lbs./acre, but it can range from about 375 lbs./acre in unfavorable years to about 725 lbs./acre in above-average years.

Resilience management. Rangeland Health Implications/Indicators: This plant community is relatively resistant to change but is at-risk of transitioning with continued stress. The herbaceous cover is intact, and plant vigor and replacement capabilities are sufficient to maintain during periods of moderate grazing pressure with recovery periods; however, species composition can be altered through long-term overutilization or increased intensity of defoliation. The overall canopy is adequate, but the shift in structure of cover and increase in bare ground opens niches for weedy species as well as slightly reduces the infiltration of snowmelt (loss to evaporation). Although minor, an increase in bare ground, shallower-rooted species, and woody cover reduces the site resiliency. Bare ground averages 25 to 35 percent, and woody cover has increased to an average of 10 to 25 percent. Litter and biological crust cover overall appears to be similar across this state (State 1). Water flow patterns and litter movement are minimal but are slightly more pronounced on steeper slopes. Incidence of pedestalling is minimal, and soils are mostly 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

Timing of grazing, Drought, Climatic shifts – Historically, the large expanses of federal lands were used during the summer exclusively or were utilized in the spring and then again in fall as sheep were trailed to forest allotments and then home again. The repetitive timing of use would have slowly removed more desirable species from the system, encouraging the rhizomatous and low-statured bunchgrasses. Long periods of drought and shifts in spring precipitation patterns have weakened and impacted the productivity and vigor of most species and has encouraged the low-statured cool-season grass-like and warm-season grass species – threadleaf sedge and blue grama. 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 this plant community. The shift in this community is marked by the decline of Indian ricegrass, with an increase in rhizomatous wheatgrasses, prairie Junegrass, threadleaf sedge, and blue grama.

Context dependence. Changes in herbivory pressure by sheep and wildlife in the area have allowed Wyoming big sagebrush to become increasingly woody and decadent. Although this has created a slight perception of increased woody canopy, the community is still dominated by cool-season perennial grasses. Overall, a stronger presence of short-statured grasses and grass-likes (blue grama, threadleaf sedge) have increased across the entire basin but has remained as a secondary component in these reference communities.

Pathway CP 1.2-1.1
Community 1.2 to 1.1

Perennial Native Grasses/Sagebrush

Needleandthread/Indian Ricegrass Plant Community

Long-term Prescribed Grazing, Brush Management - Integration of a rotational grazing system or rest-rotation with management to reduce or improve quality of the shrub canopy, will encourage the native bunchgrasses to reestablish in this community. An extended period of time (estimated at 5 to 10 years) may pass before significant change is noticed. Prescribed grazing, especially following sagebrush canopy treatments, helps to remove woody debris and expose the existing seedbank, encouraging native species. Allowing rest during critical seedling establishment and reducing competition will help recovery. Hoof action helps to incorporate the seed and litter to allow the desired bunchgrasses (needle and thread, Indian ricegrass) and rhizomatous wheatgrasses to reestablish or to increase, driving the recovery to the Reference Community (1.1). This hoof action, and brush treatment can be a tool to limit mat-forming species, maintaining the hydrologic cycle, reducing runoff. A long-term management strategy may be required before any trend towards the Reference State 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 desired 10 percent cover.

State 2
Mixed Shrubs/Bare Ground

Persistence of drought with frequent overuse leads to a decline of the herbaceous species, creating the Wyoming Big Sagebrush/Bare Ground State. Wyoming big sagebrush creates a zone of protection for understory of herbaceous species. Sagebrush and other woody species provide shade, moisture reserves, and protection from herbivory. A select array of herbaceous cover will persist in this understory and may maintain vigor in difficult conditions.

Characteristics and indicators. Sagebrush or woody vegetative cover is the prominent characteristic of this state. The understory of herbaceous cover is generally lacking or sparse in the woody cover interspaces. The woody canopy does provide a "niche" for some herbaceous species to persist.

Resilience management. This state can be exacerbated by insects and other human disturbances. The total woody canopy (foliar) cover does not necessarily increase in this community, but the percent composition by weight (annual production) is influenced by the decrease of herbaceous vegetation and the relative stability of the woody species production, creating the appearance of increased canopy cover of sagebrush. Risk of wildfire 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 specific weather conditions. Depending on the prescription of use, trailing and other erosional patterns are highly visible in this state. The loose or coarser texture of these soils allows for increased wind scour and drifting/mounding to occur with more open ground between canopy “patches,” that further hinders fire movement. Protection from wildfire and use, on a long-term perspective, can aid in the transition of a Reference Community (1.1 or 1.2) to this state as sagebrush becomes dense and decadent reducing the ability for the herbaceous component to maintain vigor. The loss of herbaceous cover leads to increased bare ground and sagebrush cover. As the site continues to weaken, the sagebrush cover is susceptible to attack by insects, disease, and old age; which can remove it from the system increasing the risk of invasion or transition to a more degraded state. The overall arid nature of coarse textured soils exacerbates the impact of drought and reduces the resilience and resistance of this site during extended dry periods. The presence of yucca on this site is not frequent, but when it does occur, it can easily become a concern, especially if frequently grazed in the winter. The growth habits of the yucca plant produces pedestalling and drift/scour patterns on the landscape. The level of variability of species in this state (State 2) remains abundant; however, only one-well defined community will be provided here, with discussion of transitions or variances from this community.

Community 2.1
Mixed Shrubs/Bare Ground

This plant community is the result of the degradation of the herbaceous understory and subsequent dominance of Wyoming big sagebrush. Annual production of sagebrush exceeds 25 percent of the total annual production and is a significant component of the plant community by cover. Remnant populations of the mid-statured cool-season grasses exist but have been greatly reduced. Yucca and spiny hopsage may be components of this community in response to the coarse textures and the potential to mound on the leeward side of sagebrush. The dominant grasses and grass-likes are needle and thread, Sandberg bluegrass, threadleaf sedge, and blue grama. Plains pricklypear cactus is more prominent on landscape. Plant interspaces have increased with the more prevalent bare ground. In comparison to the Reference Plant Community 1.1, the annual production is slightly reduced, with the shrub production increasing to compensate for the decline in herbaceous production. Although this is the only noted community phase within this state, there is a range of variability. This community is determined to be “At-Risk” due to its vulnerability to invasive weeds such as cheatgrass, Russian knapweed, or leafy spurge, if a seed source is available. The total annual production (air-dry weight) of this state averages 475 pounds per acre, but it can range from 310 lbs./acre in unfavorable years to 700 lbs./acre in above-average years.

Resilience management. Rangeland Health Implications/Indicators: This plant community is resistant to change because of the loss of herbaceous species. Increased bare ground and increased interspaces has left this community at-risk and is susceptibility to invasive species. This plant community may be more resistant to fire as less fine fuels are available and bare ground increases. 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. The plant 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 downslope.

State 3
Sod-Formers

Tillering, mat-, or sod-forming species are native and common in many communities within the Big Horn Basin. Blue grama and threadleaf sedge are the dominant grass or grass-like species within this functional group. Both species are a native component of the Reference Community; however, the tendency is for these species to increase with prolonged drought or under grazing pressure, becoming dominant. As the dominant species, they alter the hydrology of the site, increasing surface runoff. The dense and restrictive root system inhibits movement of water through and funnels surface flow around the edge of the “grass clumps,” concentrating flow into channel-like patterns, creating a drier environment for native grass species and forbs to persist.

Characteristics and indicators. The major canopy cover is comprised of blue grama and threadleaf sedge. Sagebrush and yucca may be present as well as a few other shrubs; however, most woody canopy and other herbaceous species are few. Pricklypear cactus tends to increase in this State.

Resilience management. Blue grama and threadleaf sedge tend to be resistant to management once established on the landscape. Mechanical treatment of the soil is one of the few tools found to have a strong success in altering this community once established.

Community 3.1
Sod/Sagebrush Plant Community

The loss of mid- and low-statured cool-season bunchgrasses and the persistence of sagebrush are the major characteristics of this sod-dominated community. The low, mat-forming grass and grass-like species respond and fill the voids in this plant community due to continuous season-long grazing, recurrent overutilization, prolonged drought, or shifts in climate. The effect of blue grama and threadleaf sedge, with their short-stature and dense root structure, is a decrease of water infiltration which increases channelization of runoff between vegetation patches. This effect coupled with the lack of structure to hold moisture, and further compounded by drought will continue to reduce the shrub component. A dense sod of interspersed patches of blue grama and threadleaf sedge is the major component of this community. Incidental occurrences of other perennial natives occur generally within the sagebrush canopy or the protective ring of the plains pricklypear cactus clumps. Overall, Wyoming big sagebrush has been reduced in vigor and abundance across this community phase, but it persists (average density 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. Plains pricklypear cactus is prevalent on the site, and other mid-stature cool-season 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 state is about 275 lbs./acre, but it can range from about 125 lbs./acre in unfavorable years to about 400 lbs./acre in above-average years. The higher productivity is generally in response to Wyoming big sagebrush; however, yucca and other woody species may be present as well, influencing overall production.

Resilience management. Rangeland Health Implications/Indicators: This community is at-risk of transitioning to a completely sod-bound community with no woody vegetation. The dense root mats are extremely resistant to change, with management scenarios have minimal effect (frequent and severe grazing, or the removal of grazing does not seem to have any further effect on the plant composition or structure). The shrub component will be degraded and eventually removed from the plant community under either scenario. The biotic integrity of this state is not functional and plant diversity is extremely low. The plant vigor is significantly weakened, and replacement capabilities are limited due to the reduced number of mid-stature cool-season bunchgrasses. This sod-bound plant community hinders 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 a stable state of a sod bound community creates the at-risk label. The threshold crossed to enter this state, the composition of sod-forming grasses and the lack of significant cover by other perennial grasses, leaves these two communities (3.1 and 3.2) as similar communities with only one marked shift – the presence of sagebrush in the community. Blue grama, threadleaf sedge and other tillering species will suffer a “die-back” during drought or other stressed conditions. The trend is for the central growth of these species to become decadent and then die. The plant will remain intact until disturbed (trampling, vehicle traffic, ground disturbances). Once disturbed, the plants quickly degrade leaving a central ring where the soil surface is vulnerable to erosion. This vulnerability opens a potential for native species, as well as invasive species, to gain a “toe-hold” in the community.

Community 3.2
Sod/Cactus Plant Community

The phase step from Sod/Sagebrush Community Phase (3.1) to the Sod/Cactus Community Phase (3.2) is a change in composition from an overstory of Wyoming big sagebrush to an understory of plains pricklypear cactus. The loss of sagebrush is the driving factor. Blue grama sod, with threadleaf sedge intermixed, has an increasing prominence of plains pricklypear cactus in the community. Cactus density has the potential to increase to a level that restricts the ability for livestock to move through or graze the available forage. Wyoming big sagebrush has been removed from the community with only isolated occurrences. Rubber rabbitbrush is significantly reduced but may persist. 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 replaced. Production has been significantly decreased. The dense and frequent clumps of cactus provide a niche for small, remnant populations of the mid-statured cool-season grasses to persist in the community. The ability for low-statured sod-formers to respond to amount and timing of precipitation is not as significant as other cool-season grasses, such as needle and thread and Sandberg bluegrass; however, there is still a marked swing in average production between wet and dry years. The focused production of the inflorescence and tillers is a more prominent response for these short-statured grasses. Production is provided as an average or mean and is not intended to cover the full range of production potential for this community. The resilience and resistance capacity of this community is high because of the low-statured grasses and the ability of cactus to tolerate high levels of use and the ability to maintain as other native species are depleted, including Wyoming big sagebrush. Extended periods of drought have proven to be detrimental to the health and vigor of blue grama stands across the area; however, there has been no documentation to show what species may recover in this damaged community. Studies and further observation needs to be documented to determine what the recovery potential is for a sod-bound community following significant drought die-off. Total average annual production is 225 lbs./acre, but it can range from 110 lbs./acre in unfavorable years to 425 lbs./acre in above-average years.

Resilience management. Rangeland Health Implications/Indicators: This sod-bound community is extremely resistant to change. Management (continued frequent and severe grazing to the removal of grazing) does not seem to affect the composition or structure of the plant community. The biotic integrity of this 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 mid-statured cool-season grasses and the loss of height and structure (woody component for shade and snow catch). The dense root mats of both blue grama and threadleaf sedge reduce infiltration and increase runoff. Off-site areas can be affected and degraded with excessive runoff that can cause rills and gully erosion. Water flow patterns are obvious in the bare ground interspaces 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 produces a threat of invasion of cactus. Although not documented in this LRU at this time, it has been noted in other areas of Wyoming, that plains 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. Surface disturbance (hoof action, large equipment such as vehicules and tractors, or other human impacts) can initially reduce the density of cactus, but the risk of rerootin g of the disturbed pads, may cause a rapid increase in density across an area of impact.

Pathway CP 3.1-3.2
Community 3.1 to 3.2

Sod/Sagebrush Plant Community

Sod/Cactus Plant Community

Intensive Brush Management, Fire, Frequent or Severe Grazing, Drought – The altered hydrology of a sod dominated community creates a dryer soil environment. The droughty conditions of this community reduces the vigor and over time will reduce the composition of sagebrush and other woody species within the community. The drier conditions and patchwork dynamics of the sod community reduces the potential for seedling establishment of many native grasses and shrubs. Fire has little influence on this community due to the lack of fine fuels to carry it; but in rare circumstances, isolated areas may burn within the shrub canopy. Once sagebrush is removed from this community by intense grazing pressure, drought and insect damage or by fire (rare), sagebrush is replaced in dominance by plains pricklypear cactus, and the community will phase into a sod/cactus community. In some cases, rubber rabbitbrush will persist or increase slightly on a site as sagebrush diminishes.

State 4
Invaded

Cheatgrass or downy brome (Bromus tectorum) is an aggressive annual invader that threatens rangelands across the west, including Wyoming. The ability of cheatgrass to persist through the winter under a blanket of snow and grow early allow it to take advantage of early spring precipitation and snowmelt (winter annual). Multiple growth cycles throughout a year leaves a thick litter (duff) layer and builds a significant seedbank. This annual invader has an aggressive growth habit that creates a hostile environment for most native species, including sagebrush. Climatic shifts, changes in management, and exposure to human activity are a few of the explanations for the current flush and rapid expanse across the western United States. Although cheatgrass is the most prevalent large-scale threat for rangeland managers, a variety of thistles and knapweeds, in combination with other aggressive invaders such as whitetop (hoary cress), black henbane, field bindweed, and leafy spurge are increasing in density and frequency. Each species produces their own set of challenging management issues. As new species are identified, 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. This state is characterized by the presence and then dominance of invasive/non-native species. 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. Increased access, increased travels of individuals, and other natural and man-made disturbances has opened the door for invasion in most native communities.

Resilience management. The lack of tools to achieve complete eradication, and variable success on long-term reduction of most invasive species has led to this state being resilient and resistant to change.

Community 4.1
Native Grasses/Invaded/Sagebrush Plant Community

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. This community phase (4.1) is characterized by a significant composition of invasive species (5 percent or greater) on the landscape. These invasive species have a wider scale of distribution; rather than one isolated patch in an isolated portion of the landscape. Although this community phase is susceptible to further invasion (becoming an invader driven system), if measures are taken to maintain the undesirable species at 5 to 10 percent composition, the probability of the native population persisting and possibly improving remains. However, extent of improvement is limited, and the cost and labor required determine the economic feasibility. Further degradation of this community phase increases the cost and decreases the feasibility of restoring a desired community, which makes this community phase, the “At-Risk” community. Litter cover within this phase is increasing with the duff layer specifically associated with cheatgrass. This duff layer creates a barrier that can impede water infiltration and increase runoff, accelerating erosion. This is aggravated with increased slope. The age and extent of the cheatgrass stand will determine the extent of duff in the system. Production yields of the perennial grasses and forbs are 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: Plant diversity is moderate for this phase, with perennial grasses, forbs, and shrub components still present, sustaining the diversity of the community. The plant vigor is reduced, and replacement capabilities are limited due to the limited moisture and nutrients available after cheatgrass has sprouted. Plant litter is noticeably more when compared to reference communities due to the potential biomass produced by the invasive species (species dependent). Soil erosion is minimal but will vary with species; as is the water flow patterns and pedestalling. Infiltration is unaltered or slightly reduced; however, as the duff layer or litter builds, infiltration will decrease, and runoff will increase.

Community 4.2
Invaded/Sagebrush Plant Community

As the native populations of perennial grasses and forbs are lost through overuse or disturbance, the site becomes invader-driven. Wyoming big sagebrush can compete and maintain a footprint in this community, even 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. The fine fuels or biomass produced by cheatgrass and other invasive species raises a significant threat of fire and increases the potential for fire to occur, and the possible intensity of the fire. The litter or duff layer, specifically associated with cheatgrass, is significantly higher than the native community; which creates a barrier that can impede water infiltration and increase runoff, accelerating erosion. This is aggravated with increased slope. The duff layer creates an extreme hot zone during wildfires that can sterilize the soil through volatilization of nutrients or by the formation of an ash cap that seals the soils, preventing water infiltration and seed penetration, reducing the ability for revegetation post-disturbance. New or improved strategies for invasive species control are actively researched across the western United States. High-intensity grazing with chemical control and the use of biological agents are techniques that have been trialed locally, with varying levels of success. The key management strategy, at this phase, is to reduce the fire risk and maintain the existing Wyoming big sagebrush and native perennial grass species. Maintaining the limited biotic integrity by maintaining species richness provides structure and a range of growth traits allowing adaptability of the site to varying climatic swings. Supporting the hydrologic function with the remaining woody species provides snow catchment and shade to allow a slow release of winter precipitation during spring melt providing 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 stand becomes more decadent it loses its resistance to becoming an invader-only community. This phase is prone to fire as fine fuels are more available; however, the bare ground between sagebrush plants has decreased with increased biomass of annual invaders. Plant diversity is poor, and vigor is diminished. The adaptability or replacement capabilities are limited due to the reduced number of cool-season grasses. Plant litter is noticeably more. Soil erosion is species-dependent and associated litter accumulates. The variability of the water flow and pedestalling, as well as infiltration and runoff, is determined again by the species that persist within the community.

Community 4.3
Invaded (Annual Grasses) Plant Community

Cheatgrass can grow quickly, utilizing limited resources provides a competitive advantage against mature native species. The ability of cheatgrass to produce large quantities of seed quickly, to reproduce in poor conditions, and the significant duff layer it produces limits the ability for native seedlings to establish, even when resources are available. 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. The absence of sagebrush in this community put the remnant populations of native herbaceous species at risk. However, the ability of the native cover to remain quiet under the cheatgrass canopy does allow it to persist. Plains pricklypear cactus provides a niche for natives to thrive to a lesser extent. Variability in spring storms and temperature shifts offer an opportunity for native grasses to express their resiliency, but they are not able to “outcompete” the invaders in the long term without assistance from integrated pest management. 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 that have been observed in aerial treatment trials. This generally comes from the chemical composition and the way it binds to the chemistry or nutrients in the soil, inhibiting the uptake by roots. The increased fire frequency or interval prevents sagebrush and other woody species from establishing on the site, and has negative impacts on many of the native herbaceous species in the understory. The grazing potential is limited due to the unpalatable nature of mature cheatgrass plants (chaff, prominent awns, no forage value). If grazed in early spring or late fall some of this can be avoided, but it is difficult to achieve an effective level of intensity of grazing to maintain cheatgrass, let alone reduce or eradicate cheatgrass. 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 structure and 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.

Pathway CP 4.1-4.2
Community 4.1 to 4.2

Frequent or Severe Grazing, Wildfire, Drought – Climatic stress (drought, changes in timing of precipitation), wildfire, or other natural disturbances will hinder the native species, reducing their ability to maintain their footprint in the plant community. Continued, long-term, stress or the complication with 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. Grazing management to reduce invasive species can be effective. Utilizing the early green up and the late growth habits of cheatgrass can be an added benefit for native species as well as control further spread of invasive species. However, if timing of this grazing or intensity is not done properly, further degradation to the native community can occur, allowing invasive species to become more dominant in the community.

Pathway CP 4.1-4.3
Community 4.1 to 4.3

Native Grasses/Invaded/Sagebrush Plant Community

Invaded (Annual Grasses) Plant Community

Frequent or Severe Grazing, Wildfire, Drought - The loss of the sagebrush brush canopy due to fire, drought, or herbivory, opens the potential for extensive invasion by weedy species especially cheatgrass. Continued over utilization by large herbivores or extended periods of drought will further stress the native grasses leaving no barrier against invasive species. Once the sagebrush canopy is lost, resulting changes in hydrology inhibit or prevent recovery of the system without major inputs.

Pathway CP 4.2-4.1
Community 4.2 to 4.1

Integrated Pest Management/Weed Control and Long-term Prescribed Grazing - Prescribed grazing to allow use of the invasive species with minimal impact to the native population, in conjunction with invasive species control will allow the community to regain or maintain potential. Currently, eradication of invasive species has not been achieved on a large-scale basis, and sustained control requires intensive inputs over the course of several years. To maintain the system with no further degradation requires a dual approach of both long-term prescribed grazing with an intensive weed management (integrated pest management) plan. No one single practice can sustain this phase, it requires intensive management to prevent the transition to Community 4.3 – Invaders (Annuals).

Pathway CP 4.2-4.3
Community 4.2 to 4.3

Catastrophic Disturbance – Removal of sagebrush and desirable herbaceous cover by fire, land clearing, or similar events, provides the opportunity for a significant invasion by weedy species especially cheatgrass. Large-scale invasions, especially after catastrophic wildfires, leave the landscape barren of all native species. Isolated remnants may be found in pockets throughout the landscape. However, if no attempt to apply weed control or with further disturbances (multiple fires), the native species will remain hidden or will be removed completely from the community. The ability for this community to revert to a less degraded community within this state is not feasible without implementation of an integrated pest management plan.

State 5
Altered

Difficulties in maintaining delivery systems and dependable supply of irrigation water has limited the economic feasibility to maintain all farmed lands. Increased energy development and the expansion of recreational land uses (including hunting) has changed the face of rangelands. The broken nature of the rim provides more topographic relief for movement of wild game, yet access is still easy to moderate for wheeled traffic. Although the disturbance footprints within this LRU are not as contiguous as within the core, old homestead locations, abandoned crop fields, roads, recreational facilities, and energy development have left their marks. 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 will not replace the original function and factors to an undisturbed state. These "altered" lands may, after significant inputs and time, resemble the Reference Communities (1.1 or 1.2), but they will respond and 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 the Reference State. Location or site-specific investigation is needed to determine if a disturbed or reclaimed area still meets site characteristics. The time required to allow the redevelop ment of structure and the cryptogrammic crust, as well as any impact to chemistry, is beyond the natural function of management. The initial flush of vegetation is kochia and Russian thistle and mustards, a successional plant community. The site begins its own recovery, but the time required to return to the original conditions (pre-disturbance) is outside of feasible consideration. The site, however, may become similar in composition to the Reference State, but the integrity of the soil is altered, changing the potential of the site.

Characteristics and indicators. This state is characterized by a landscape that has been mechanically manipulated or had significant soil disturbance. Early successional plant communities, evidence of farming (field edges, cultivation rows, etc.) or the presence of introduced species (crested wheatgrasses, russian wildrye, etc.) are indicators of this state.

Community 5.1
Disturbed/Degraded Lands 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. 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 high for successional communities but is usually lacking in the structural/functional groups. 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).

Community 5.2
Reclaimed Lands Plant Community

Shifts in reclamation practices over the last several decades have altered the success and stability of reclaiming a site. The historic use of crested wheatgrass created stable stands that persist long-term, however palatability and vigor decrease with time. Species creep into surrounding native communities as well as native species recovering within crested wheatgrass stands have been documented within this LRU. Russian wildrye and varieties of rhizomatous and bunch-wheatgrasses were used more recently in mixes to help increase diversity and longevity of seedings. But now, on federal lands specifically the use of native species is required. Although success for vegetative seeding is low to moderate in this LRU, due to the variable amounts and timing of precipitation, limited areas along pipeline corridors, well sites or pad sites, and along transportation corridors have succeeded. The growth curve of this plant community will vary depending on 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 region must be considered.

Resilience management. Rangeland Health Implications/Indicators: Seeding prescriptions determine the resistance to change and resilience against invasive species and erosion. 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 on the seedling density, 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 practices).

Pathway CP 5.1-5.2
Community 5.1 to 5.2

Seeding, Brush Management, Integrated Pest Management, Prescribed grazing – Planning and selection of best practices for site improvement need to be implemented to stabilize this site. The erosive nature of the soil one disturbed increases the need to stabilize the site quickly. Species selection is key and may require a cover crop to prevent erosion prior to seedling establishment. Direct seeding or minimal soil tillage may be the best approach to allow establishment of grasses within the residue of the cover crop. The arid nature of this site will create its own challenge with the lack of moisture and narrow window for seeding. The general nature of native seeds common for these sites are difficult to drill. Mulching may be required to prevent loss of moisture and wind scour (loss of seed).

Context dependence. The success or outcome of this transition is contingent on the inputs involved. These inputs will include - soil manipulation (seedbed prep), seed selection, seeding methods, and post seeding treatments. Climate and management are secondary factors affecting this transition.

Pathway CP 5.2-5.1
Community 5.2 to 5.1

No use, No Fire, Long Term Prescribed Grazing, Frequent or Severe Grazing – Maintenance of a seeded community is needed to prevent a decline in vigor and a corresponding shift in composition. The altered soil properties by mechanical or natural disturbance prevents the plant community from responding like the native community. Monitoring range trend over time helps 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 the disturbed community.

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 climatic and human-induced. Frequent or high-intensity herbivory weakens the ability for desirable grasses to persist, especially during periods of prolonged drought. The composition will shift to predominantly Wyoming big sagebrush as the herbaceous cover declines. Over extended periods of time, the sagebrush canopy will increase in density, preventing the recovery without intervention. The illusion of crossing the threshold to State 2 is captured with fluctuating precipitation patterns affecting production of prominent plants within this system. A marked loss of herbaceous cover and diversity, increased bare ground, and lack of litter over multiple monitoring cycles provides the evidence that the transition to State 2 has occurred, and is not an annual climatic response. It is important to recognize that the number of actual sagebrush plants may not increase to cause this shift. Rather the loss of herbaceous composition and increase in the canopy cover of woody species is the larger factor (creates the illusion of increased number of plants when it is the size and age that is more likely to change).

Constraints to recovery. The possible lack or limited seed-sources for the key mid-stature, cool-season bunchgrasses is the major recovery constraint for this State.

Transition T 1-3
State 1 to 3

Frequent grazing (yearlong), brush management, or fire with droughtSevere and frequent grazing (by livestock or any other large ungulates) reduces vigor and presence of key species. As needle and thread and Indian ricegrass begin to decline, shorter-statured grasses become dominant. Animal disturbance (hoof impact) reduces the bunchgrass component through damage to the crown of the plant, but also in some instance by allowing repeated defoliation of the desirable species, reducing recovery potential and ground cover for insulation and snow catch. The damage and repeated defoliation weakens, and over time, removes select species. The open canopy and hoof impact encourages species that are tolerant to trampling and that can utilize the small bursts of spring and summer moisture, these species are generally mat or sod-forming species such as blue grama and threadleaf sedge. Prolonged drought stresses the plants and opens the canopy for these short-statured grasses to fill in the interspaces. The shallow, dense root mats will continue to spread over time. The added removal of sagebrush with animal impacts, fire, or brush management may open the canopy more and aid in establishing this sod community. Season of use and intensity of grazing (time and timing) is a trigger that can reduce the risk of transitioning, or if done poorly can force the transition to occur rapidly. The Reference State (1.1 and 1.2) is dominated by cool-season species. Provided the area receives good spring moisture, growth and maturity of these plants can happen quickly within the first two weeks of June, while blue grama is just beginning. By alternating when the community is grazed, providing periods of rest during the critical initial green-up and growth in the spring, and allowing recovery time before the community is grazed again within the year, allows the bunchgrasses and rhizomatous grasses to maintain vigor and production. This also allows for summer use when the warm-season grasses are growing (blue grama) which will help to utilize this species and maintain cover.

Constraints to recovery. The resiliency of the mat-forming (sod-forming) grasses is the recovery constraint for this transition. Blue grama and threadleaf sedge, once established in significant composition, are resistant to management changes and require some level of mechanical manipulation to allow other native species to increase (re-establish) in this community.

Restoration pathway R 2-1
State 2 to 1

Prescribed grazing with brush management or wildfire—Treatment to thin or rejuvenate the sagebrush canopy is necessary to allow and encourage native perennial grasses to respond to improved moisture and sunlight. Prescribed grazing is required in conjunction with brush management to prevent overuse of the exposed grasses allowing this community to recover. Treatment will vary depending on the current 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 grass 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. Climate and treatment conditions during and following a fire has a larger impact on the community. It is crucial to investigate the immediate and surrounding areas of a treatment site to ensure no invasive species (cheatgrass) are present.

Context dependence. In some instances, when sagebrush canopy is not excessive but the understory of herbaceous species is lacking, seeding of native cultivars may be necessary to encourage the grasses to re-establish.

Transition T 2-3
State 2 to 3

Drought, disease or insect damage, overuse, 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, creating a sagebrush/sod community that is resistant to change by grazing management. Impacts to sagebrush by disease or insect damage, as well as drought or herbivory, will shift this community to the secondary community phase with cactus as a subdominant cover with blue grama and threadleaf sedge. Extended periods of drought in combination with a change in the amount and timing of precipitation and spring snowmelt has allowed the warm-season grass, blue grama, to out-compete cool-season natives such as needle and thread. Climate change is widely debated and speculated; however, the documented shifts in climatic curves, as well as large-scale transitions to this community under different management scenarios, highlights climate as a key player – not just use and management. Further research is needed to identify the factor for each site-specific situation.

Constraints to recovery. The loss of or lack of woody canopy, primarily sagebrush, and the need for mechanical treatment to reduce/remove the sod-formers are the major constraints for recovery of this state.

Transition T 2-4
State 2 to 4

Fire (wild or prescribed), frequent or severe grazing, drought with insect damage/brush managementThroughout most of this LRU, there are seed sources present for cheatgrass, knapweed, and other invasive species. Removal or thinning of the canopy and displacement of the soil surface by disturbance (fire, drought, disease/insect damage to sagebrush, or ground/soil disturbance including impacts by grazing large herbivores or recreational activities), creates a niche for invasive/undesirable weeds. Invasions start with one or two isolated plants, that if caught can be treated and an infestation avoided; however, when unseen or ignored, the population grows exponentially with time. In some cases, once the invasive species are established, they can create their own habitat, reducing the ability for native species to compete for the limited resources. The open canopy of the Sagebrush/Bare Ground State is vulnerable to invasive species without further influence. With continued overuse, drought, or insect damage or 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.

Constraints to recovery. The inability to eradicate or achieve long-term control of most invasive species is the constraint to recovery for this State transition.

Transition T 3-4
State 3 to 4

Frequent and severe grazing, drought, disturbance with a seed source presentResistance to invasion of the sod-dominated community is presumed due to the lack of extensive bare ground and the aggressive and persistent nature of blue grama and threadleaf sedge. This community also has a minimal risk of wildfire because of the lack of fine fuels and reduced sagebrush canopy. The increased interspatial pattern of 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 of low-statured grasses, opening more surface to invaders, such as cheatgrass and knapweeds. 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, the extent of spread is limited, but it is still extremely difficult to manage, and eradication is not feasible. Once the invasive species have become prevalent on the landscape (>5 percent composition), the community crosses the threshold into the Invaded/Sagebrush State (State 4).

Constraints to recovery. The lack of sufficient tools to eradicate or gain long-term control of most invasive species is the constraint to recovery for this state.

Restoration pathway R 4-5
State 4 to 5

Integrated pest management, with seedingIntegrated pest management and intense weed control as part of seedbed preparation and after seeding will be necessary to overcome a severe weed infestation. Preparation of the target area and utilization of improved varieties, native seed, or (where appropriate) introduced species suited for intended land use increase the success of removing the 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. The limited success and difficulties in reestablishing sagebrush also limit the site potential. Due to the need to till (turn the soil) for seedbed preparation reduces soil stability by breaking down soil structure and alters the hydrologic cycle by changing the infiltration and percolation rates of the soil. The alteration of the soil properties prevents the soils from reacting the same to management and environmental changes, so transitions to a reclaimed or altered state (State 5).

Transition T 5-4
State 5 to 4

No use, fire (wild or prescribed), frequent or severe grazing, drought with seed source presentPost-disturbance and during reclamation processes, management is required to prevent a reoccurrence or a new infestation of weeds. Wildfire, prescribed burning, drought, or frequent and severe overutilization by herbivores can be a source of the disturbance that either opens the canopy or introduces the species to the location. Extended periods of non-use can create loose soils, reducing vigor and health of the native population. The resulting die-back allows the community to become vulnerable to weed invasions. This invasion triggers the transition to the Invaded State.

Constraints to recovery. The inability to or the financial cost of the inputs to eradicate or successfully control invasive species is one contraint to recovery. Another is the seed selection to compete with the invasive species that are affecting the site.