State 1
Reference

The Reference state, State 1, is labeled as the Bunchgrass and Sagebrush state. Wyoming big sagebrush and mid-stature bunchgrasses are the dominant contributors to composition with a notable cover of perennial forbs. Cover in this Reference State is reduced (increased bare ground) from similar ecological sites (Loamy and Sandy), due to the gravel substratum that reduces the available moisture in the lower soil profile.

Characteristics and indicators. This State is characterized by ten percent or less composition by cover of Wyoming big sagebrush, with a dominant understory of bluebunch wheatgrass, needle and thread, and Indian ricegrass (30-50 percent composition). Areas of western wheatgrass exist with the other minor components including prairie Junegrass, bottlebrush squirreltail, Sandberg bluegrass, threadleaf sedge, and blue grama.

Resilience management. The plant community is diverse and is adapted to the arid and unpredictable nature of the environment creating a resilient community. In extended periods of drought, species such as needle and thread and western wheatgrass are able to limit production until conditions are suitable. Once conditions have improved they are prolific producers. Sandberg bluegrass is another species that can respond quickly to the drastically changing precipitation and climate patterns of the Big Horn Basin. 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 time of 50-120 years or more in arid systems (Baker, 2006) and with grazing pressure by large ungulates (elk, bison, deer, or antelope).

Community 1.1
Bluebunch Wheatgrass/Needle and Thread

Figure 7. Bluebunch wheatgrass and needle and thread community with a healthy composition of Sandberg bluegrass after a cool wet spring.

Community Phase 1.1, Bluebunch Wheatgrass/Needle and Thread is captured as the Reference Plant Community. This Community Phase evolved with grazing by large herbivores. The potential vegetation cover is about 75 percent grasses or grass-like plants, 15 percent forbs, and 10 percent woody plants.

Dominant grasses include needle and thread, bluebunch wheatgrass, and rhizomatous wheatgrasses. Grasses and grass-like species of secondary importance include Sandberg bluegrass, prairie Junegrass, bottlebrush squirreltail, threadleaf sedge, and blue grama. A variety of forbs are found in this community including fleabanes, wild parsley, fringed sagewort, and milkvetch. Wyoming big sagebrush, is a conspicuous component 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 375 lbs./acre, but it can range from about 200 lbs./acre in unfavorable years to about 550 lbs./acre in above-average years.

Resilience management. 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 bluebunch wheatgrass), rhizomatous species (western wheatgrass and thickspike wheatgrass), and the short-statured bunchgrasses (prairie Junegrass, Sandberg bluegrass, and bottlebrush squirreltail) 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

Figure 10. The prominent cover of Sandberg bluegrass and rhizomatous wheatgrasses and lack of bluebunch wheatgrass indicates the transition to Community Phase 1.2.

The secondary community phase of the Reference State (1.2), is captured as the At-Risk Community. Although it is similar with only minor shifts in composition and function, the decrease in needle and thread 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. 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 major understory of grasses and grass-like plants includes needle and thread, rhizomatous wheatgrasses, blue grama, Sandberg bluegrass, and bottlebrush squirreltail. The variety of forbs and half-shrubs commonly found include scarlet globemallow, milkvetches, spiny phlox, and fringed sagewort. 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 and threadleaf sedge has increased within this community, as has Wyoming big sagebrush; however, they are not the most prevalent grass species. The shift in species has an impact on the hydrology of the site. Plains pricklypear cactus will also have increased but occurs only in small patches. Needle and thread has decreased and may occur in only trace amounts under the sagebrush canopy or within the patches of pricklypear; whereas rhizomatous wheatgrasses and bottlebrush squirreltail have maintained and are a common component in this community.

The total annual production (air-dry weight) of this community is about 300 pounds per acre, but it can range from about 200 lbs./acre in unfavorable years to about 600 lbs./acre in above average years.

Resilience management. This plant community is resistant to change. The herbaceous 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 25 to 40 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 1.1A
Community 1.1 to 1.2

Bluebunch Wheatgrass/Needle and Thread

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 warm-season grass species such as 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 needle and thread, with an increase in rhizomatous wheatgrasses, Sandberg bluegrass, bottlebrush squirreltail, 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 (blue grama, Sandberg bluegrass) have increased across the entire basin but has remained as a secondary component in these reference communities.

Pathway 1.2A
Community 1.2 to 1.1

Perennial Native Grasses/Sagebrush

Bluebunch Wheatgrass/Needle and Thread

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, bluebunch wheatgrass) 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 Shrub and Bare Ground

Frequent and severe use 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 extended periods of drought, insects and other natural and human disturbances. 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 gravelly and coarse textured lower soil profile provides the opportunistic shrubs such as yellow and rubber rabbitbrush, and fringed sagewort to establish along with Wyoming big sagebrush. These shrubs provide a protective niche for most herbaceous understory to maintain a minimal cover 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 grass cover declines and the plant community continues to weaken, the sagebrush and other shrub cover is susceptible to attack by insects, disease, and age. The loss of the woody cover from the system places this State at-risk of invasion or transition to a more degraded state. The lack of water retention lower in the soil profile exacerbates the impact of drought and limits the resiliency of the Shallow to Gravel Ecological site. Animal trailing, foot and vehicle trails and other erosional patterns are highly visible in this State. Loss of top soil exposing the gravel layers is a potential with the increased wind and water erosion risks within this State. Risk of wildfire within this state is marginal due to the lack of fine fuels within the understory; however, the canopy of the woody vegetation will carry a fire under certain weather conditions. Fire is a significant risk to this community because of the potential to remove all native vegetation. The exposed community is vulnerable to erosion and invasion by cheatgrass with no native competition and a lack of native seed source to allow recovery. Loss of sagebrush reduces the hydrology further hindering the recovery potential.

Community 2.1
Sagebrush/Bare Ground

Figure 12. The Sagebrush/Bare Ground State as it is transitioning to the Invaded State.

This plant community is the result of frequent and severe grazing or similar disturbance that weakened and removed the herbaceous understory. The shrub canopy is still intact and creates a distinct community. Wyoming big sagebrush dominates this plant community, with the annual production of sagebrush exceeding 25 percent. The desirable mid-statured cool-season grasses have been greatly reduced, and typically reside within the crown cover of sagebrush.

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. Sagebrush, other woody cover, and cactus maintain production even though herbaceous production has declined. This community is vulnerable to invasive weeds such as cheatgrass, Russian knapweed, or flixweed if a seed source is available. This community is at-risk of transitioning to the Invaded State.

The total annual production (air-dry weight) of this state averages 275 pounds per acre, but it can range from 150 lbs./acre in unfavorable years to 500 lbs./acre in above average years.

Resilience management. Changes in management alone has minimal impact in this community, it is relatively resistant to change for native cover. Plant diversity is moderate to poor 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 Bound

The dominant sod-forming grasses that currently exists within this LRU and subset is blue grama and threadleaf sedge. Both blue grama and threadleaf sedge are native components in Reference communities within this ecological site. The trend is for these species to increase, becoming the dominant cover, with prolonged drought, shifts in climate, or under grazing pressure.

Characteristics and indicators. This community is characterized by a dominance of blue grama with interspersed patches of threadleaf sedge.. Remnants of the other key vegetation will persist, but is limited by the dense mats created by the sod-formers. The remnants are restricted to the protective niche within sagebrush canopy or cactus clumps.

Resilience management. Blue grama and threadleaf sedge effectively alters the hydrology of the site by increasing the surface runoff from the dense shallow root system that inhibits the movement of water through the soil surface. This root mat directs surface flow around the edge of the mat concentrating flow into channel-like patterns and off-site. This loss of surface moisture creates a drier environment for native grass species and forbs to persist.

Community 3.1
Sod-formers/Sagebrush

Figure 14. A sod-bound community of threadleaf sedge and Wyoming big sagebrush.

Dense, interspersed patches of blue grama and threadleaf sedge sod is the major component 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).

This plant community is the result of continuous season-long grazing, or prolonged drought.
This plant stress 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's and threadleaf sedge's short, dense root structure is decreased 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.

When compared to the Reference Plant Communities 1.1 and 1.2, blue grama and threadleaf has increased significantly, making up 30 to 60 percent of the canopy. Pricklypear cactus is prevalent on the site with scattered fringed sagewort. Other cool-season mid-statured grasses, perennial forbs, and most shrubs have been greatly reduced. Production has significantly decreased and bare ground is variable.

The total annual production (air-dry weight) of this community phase is about 200 pounds
per acre, but it can range from about 100 lbs./acre in unfavorable years to about 350 lbs./acre in above average years.

Resilience management. The short-statured tillering plants are resistant to change. No added effect to the plant composition or structure is apparent with continued frequent and severe use. Removal of grazing (non-use) shows little to no improvement of the community. The shrub component is at-risk of degradation under any management. 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 significantly reduces water infiltration, increasing runoff. The sod covered soil is protected, however interspaces or edges 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 function is degraded with the impact of runoff and its affects to adjoining sites. This community can improve with intensive management requiring mechanical manipulation and seeding. However, this community is not capable of returning to the Reference State. Extended periods of drought stress creates a die off or die-back of blue grama. 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). Surface disturbances will break up the mat crowns in their fragile state, leaving the surface more vulnerable to erosion. Threadleaf sedge will respond to extended drought or intensive use similar to blue grama. Rings are common on the landscape in this community in areas of intensive use and in drier bands within the subset.

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, extensive grazing impacts, insect damage, other natural disturbance or any combination there of, has weakened the native composition allowing invasion.

Resilience management. The competitive nature of annuals and other invasive species creates a hostile environment that restrict the native species, inhibits control and makes it implausible to attain complete eradication once an invasive species has established on the landscape. Severity and scale of invasion will make a difference in the limitations of the site.

Community 4.1
Native/Invasive/Sagebrush

Figure 16. Field Cottonrose is heavily populated within the native canopy of this community. Sagebrush was lost following a fire.

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. 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

Figure 17. Cheatgrass is dominant in this community, although there are a few remnant natives left, they are struggling to thrive.

Community Phase 4.2 is characterized by the dominance of invasive species with a component of sagebrush. However, only remnant populations of native species persist in the community and little or no native recruitment is occurring . 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 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. 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

Downy brome, better known as cheatgrass (Bromus tectorum), can green-up and grow late into the fall and green-up early spring before snow melt. This growth pattern allows cheatgrass to utilize fall and spring resources, that are otherwise stored for the cool-season native vegetation, before they can 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 from binding to the mineralogy of the soil, inhibiting the uptake of nutrients by the 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. 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 negates the purpose of intensively grazing the location. In smaller invaded sites or under certain conditions, grazing can be used as a tool within the integrated pest management toolbox, but it is not effective alone.

Resilience management. This plant community is resistant to change. Plant diversity is poor. The plant vigor is diminished, and replacement capabilities are non-existent due to the loss of cool-season grasses. Plant litter is noticeably more when compared to Reference communities in response to the dense duff layer created by cheatgrass. Soil erosion 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 4.1A
Community 4.1 to 4.2

Native/Invasive/Sagebrush

Invasive/Sagebrush

Frequent or severe grazing, wildfire, and drought— Wildfire is plausibe with the increasing cover by invasive species (cheatgrass). Drought or other climatic factors will continue to hinder the native species, reducing their ability to maintain their footprint in the plant community. Continued stress of frequent or severe grazing pressure from wildlife and livestock can reduce the native composition to an unsustainable population and allow the invasive species to dominate.

Pathway 4.1B
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 monoculture stand of invasive species. With the increase in fine fuels created by cheatgrass and other invasive species, the wildfire risk rises. Fire will trigger a shift to an invader-dominated community. 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 4.2A
Community 4.2 to 4.1

Invasive/Sagebrush

Native/Invasive/Sagebrush

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. 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 and invasive species have a secondary flush of growth. This is more typical in species such as knapweeds, whitetop, and specifically cheatgrass (downy brome). 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 established in the community.

Pathway 4.2B
Community 4.2 to 4.3

Catastrophic events, extreme grazing, 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). The establishment of invasive species will become a near-monoculture. The loss of sagebrush, the increased litter biomass that inhibits infiltration will increase the risk of fire and inhibit recruitment of native species.

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 Altered state could be drafted as a alternative land use 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. The Shallow to Gravel ecological site, once mined or tilled, potentially will lose the top soil or gain chemistry that could potentially change the ecological site the soil would key to. In some cases (site by site consideration), recorrelation of a location may be needed. 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.

Community 5.1
Altered/Degraded

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 pipelien corridors, 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. The plant community is variable as a factor of the age of the stand and the stage of successional tendencies of the location. The specific community composition will determine the stablity (resilient/resistant) of the community. 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 strong diversity, but limited structure and 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).

Transition T1A
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/<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=2BARE" target="_blank" title="Open in plants.usda.gov"><i>Bare Ground</i></a> 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/<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=2BARE" target="_blank" title="Open in plants.usda.gov"><i>Bare Ground</i></a> 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 T1B
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 R2A
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 T2A
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 T2B
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/<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=2BARE" target="_blank" title="Open in plants.usda.gov"><i>Bare Ground</i></a> 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 T3A
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 R4A
State 4 to 5

Integrated pest management with seeding—Integrated pest management with intense weed control pre- and post-seeding is necessary to overcome a severe weed infestation. Thorough seedbed preparation and use of improved varieties (native and introduced species) suited for the intended land use improves the success potential. Seed mixes are generally designed to be similar to the Reference Community Phase (1.1). The limited success of seedings, lack of seed sources for all native species, the mechanical preparation of the seedbed alters soil stability and hydrologic functions, which in turn inhibits the 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 non-disturbed native community will. Once significant soil disturbance occurs, the community will remain in 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 T5A
State 5 to 4

No use, fire (wild or prescribed), frequent or severe grazing, drought with seed source present—Lack of management to prevent further disturbance or lack of use following reclamation allows 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. Loss of vigor and increased bare ground makes the community vulnerable to weed invasions. Frequent or severe grazing, drought, or fire will also open the canopy and assist with the incorporation of seed sources encouraging an invasion and transition to the 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.