State 1
Rhizomatous Wheatgrass/Sagebrush

Figure 8. Reference State for Loamy Wind River Basin Rim.

The reference state for the Loamy Wind River Basin Core ecological site is chracterized by the dominance of rhizomatous wheatgrasses, with the scattered overstore of Wyoming big sagebrush State (State 1). This state was maintained with the grazing of large ungulates, mainly wild/feral horses, deer, and antelope; as well as domestic livestock use. This area was historically sheep and has shifted to predominately cattle, however there are still localized bands of sheep that utilize allotments within the LRU. Fire has had only a minor roll within this LRU. Small, lightening induced burns occur, but with no significant frequency.

Characteristics and indicators. Rhizomatous Wheatgrasses/Sagebrush State (State 1 - Reference) is characterized by the key species including: 15% or less composition by cover of Wyoming big sagebrush, rhizomatous wheatgrasses (western and thickspike) (<30%), needleandthread, and Indian ricegrass, with and isolated areas of bluebunch wheatgrass. Minor component to the overall composition are Sandberg bluegrass, bottlebrush squirreltail, prairie junegrass, blue grama, and threadleaf sedge.

Community 1.1
Rhizomatous Wheatgrass/Needleandthread/Sagebrush

Figure 9. Reference Community (1.1) in the Loamy Wind River Basin Rim ecological site.

The reference community (1.1) is declining on the landscape. Change or shifts in timing of precipitation, temperature (spring warm up/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 composition is 75% grasses or grass-like plants, 10% forbs, and 15% woody plants. Mid-stature cool-season grasses dominate this state. This plant community can be found on areas that are properly managed with grazing, and on areas receiving occasional short periods of rest. Historically, the reference state evolved under a low fire frequency (estimated to be 195 to 235 years between burns on the same community patch, with a post fire recover timeframe of 50-120 years or more for sagebrush in arid systems – Baker 2006) and with grazing pressure by large ungulates (deer, antelope, and wild horses primarily; but isolated areas of elk). Changes in herbivory pressure from livestock and wildlife in the area have allowed Wyoming big sagebrush to become increasingly woody and low in vigor. The community is dominated by cool-season perennial grasses, which thrive between and within the sagebrush canopy and cover of other desirable shrubby species –rabbitbrush and winterfat. A stronger presence of short, warm-season grasses (blue grama) and grass-likes (threadleaf sedge) have increased across the entire basin, but has remained as secondary cover in the reference communities. Dominant grasses include western and thickspike wheatgrass and needleandthread. Grass species of secondary importance include bluebunch and Montana wheatgrass, Indian ricegrass, and bottlebrush squirreltail. Minor grasses and grass-likes include Sandberg bluegrass, threadleaf sedge, and blue grama. Forbs commonly found in this plant community include scarlet globemallow, milkvetches/sweet vetches, desert parsley, fleabanes, and phlox. Sagebrush can make up to 15% of the annual production. The overstory of sagebrush and understory of grass and forbs provide a diverse plant community. The total annual production (air-dry weight) of this community phase is about 575 pounds per acre, but it can range from about 255 lbs./acre in unfavorable years to about 825 lbs./acre in above average years.

Resilience management. The plant community diversity enables a high drought tolerance, allowing persistence in the limiting climatic conditions of the Wind River Basin. The structural diversity of Wyoming big sagebrush in conjunction with the rhizomatous species (western wheatgrass and thickspike wheatgrass), mid-stature bunchgrasses (needleandthread and Indian ricegrass), and the secondary mid-stature bunchgrasses (prairie junegrass, Sandberg bluegrass, and bottlebrush squirreltail – rare areas of bluebunch wheatgrass) helps to provide snow catch and shade to capture and hold moisture, maximizing availability during the growing season. The site hydrology in combination with the adaptability of the plants to maintain herbaceous cover in variable weather patterns, adds to the drought tolerance and resilience of this community. Unlike the relative constant presence of rhizomatous wheatgrasses, needleandthread is dependent on early spring moisture to perform well. In years with late spring early summer moisture needleandthread will remain dormant or quiet, while prairie junegrass will produce an excellent cover. Whereas years 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 needleandthread. The persistence and adaptability from year to year of these species allows for quick recovery once “normal” precipitation returns. This variability will shift the community between phase 1 and 2 with extended periods of drought, grazing use changes, and other natural and human derived impacts; but is not at risk of transitioning into a different state unless a catastrophic impact occurs. Rangeland health factors are captured as the character traits of this community (1.1) – including: site/soil stability, watershed function, and biologic integrity.

Community 1.2
Perennial Native Grasses/Sagebrush

Figure 11. At-risk community in the Reference State (1.2).

This site is very similar to the Reference community (1.1). The community can be found on areas that have had impacts outside the natural disturbance regime (over utilization, repetitive growing season use, or are in a positive trend with effective management). The community has seen needleandthread as well as western wheatgrass decline in vigor and abundance while Wyoming big sagebrush, Sandberg bluegrass and blue grama have increased in the system. The community composition has shifted to 65% grasses or grass-like, 10% forbs, and 25% woody species. This community (1.2) still maintains a dominance of cool season mid-stature grasses. The major grasses include Sandberg bluegrass, prairie junegrass, bottlebrush squirreltail and blue grama. Western wheatgrass and needleandthread have declined, but are still components in the system. A variety of forbs and half-shrubs also occur, as shown in the following table. Wyoming big sagebrush is a conspicuous element of this community phase, and comprises 15 to 25% of the annual production. Blue grama and threadleaf sedge have increased, making up at least 5-10% of the understory. These species have a significant impact on infiltration rates and increase runoff due to their dense shallow root systems. Plains prickly pear cactus may have increased. Woolly plantain and six-weeks fescue are beginning to establish a small footprint in this community. The total annual production (air-dry weight) of this community is about 610 lbs/acre, but it can range from about 260 lbs./acre in unfavorable years to about 875 lbs./acre in above average years.

Resilience management. This plant community is resistant to change. The overall canopy is adequate to protect the site. However, bare ground has increased on the landscape due to the arid nature and increasing woody cover. Bare ground averages 25 to 35%; woody cover has increased due to reduced herbaceous cover, to an average of 15 to 25% cover. Litter overall appears to be similar across this state. Similarly, the biological crust cover does not vary. The herbaceous species are well adapted to grazing; and plant vigor and replacement capabilities are sufficient, but are limited by precipitation. Water flow patterns and litter movement may be occurring but only on steeper slopes. Incidence of pedestalling is minimal, and soils are mostly stable with minimum loss of the surface soil. The watershed is functioning and the biotic community is intact.

Pathway CP 1.1-1.2
Community 1.1 to 1.2

Rhizomatous Wheatgrass/Needleandthread/Sagebrush

Perennial Native Grasses/Sagebrush

Timing of Grazing, Drought, Climatic shifts – The increase in blue grama and threadleaf sedge throughout the system is not well understood. However, inferences to the drivers can be made. Historically, this site was used during the spring and fall as livestock were held before moving to summer allotments (mountains and foothills). The repetitive timing of use on select species slowly reduced or removed these plants from the system. Long periods of drought and shifts in spring precipitation patterns have weakened and affected the productivity and vigor of most species, leaving a harsh climate for re-establishment of these species. The historic shift from sheep to cattle dominated grazing and changes in grazing management strategies has affected the plant communities (positively and negatively). However, drought and other climatic patterns pose a significant threat to the integrity of the reference plant community.

Pathway CP 1.2-1.1
Community 1.2 to 1.1

Perennial Native Grasses/Sagebrush

Rhizomatous Wheatgrass/Needleandthread/Sagebrush

Long-term Prescribed Grazing, Brush Management - With integration of a rotational grazing system (i.e. rest-rotation), and with practices used to reduce shrub canopy, the native bunchgrasses will begin to reestablish in this community, but it may take 5 to 10 years before significant change is noticed. Targeted prescribed grazing, especially following sagebrush canopy treatments helps to remove woody debris and exposes a seedbank to encourage the native species. Allowing rest during critical seedling establishment stages and reducing competition of less desirable native species will help recovery. Hoof action helps to break up duff layers and open the seedbed to allow the desired wheatgrasses and bunchgrasses such as western wheatgrass, Indian ricegrass, and needleandthread to reestablish or to increase, driving the recovery to the reference community (1.1). A long-term management strategy may be required before any trend towards reference is noticed. The overstory of Wyoming big sagebrush is the factor that could require mechanical manipulation to reduce and rejuvenate the canopy and composition to the desired 15%. The sod forming species are a secondary concern in the transition away from reference. Blue grama has increased, but is still below 10% of the total composition, and can be minimized with grazing management strategies (hoof action).

State 2
Sagebrush/Bare Ground

Figure 14. Sagebrush/Bare Ground State with rhziomatous wheatgrasses and sandberg bluegrass.

The remaining herbaceous understory utilizes the moisture and shelter provided by the canopy of Wyoming big sagebrush to maintain vigor in difficult conditions. Persistence of drought and/or frequent over use by livestock and/or wildlife leads to a decline of the herbaceous understory, creating the Wyoming Big Sagebrush / Bare Ground State. Total sagebrush canopy increases in percent composition by cover. With the decrease of herbaceous vegetation production, the canopy of sagebrush appears to increase. Lack of fine fuels to carry a fire leave this state at a minimal risk of wildfire. However, with the right weather conditions (dry, hot winds), the sagebrush canopy may easily carry a fire. Depending on the current livestock management, trailing and other erosional patterns may be highly visible in this state. The production and function of this state can be altered by the health and vigor of the sagebrush, establishment of other woody species and the intensity of the herbivory. Long-term protection from wildfire and grazing can advance the transition of a reference community (1.1 or 1.2) to this state (2). As sagebrush becomes dense and mature, the herbaceous component declines in vigor, bare ground and sagebrush cover increase. Further decline in this state, leaves the sagebrush cover susceptible to attack by insects, disease, and general old age. This community is now at risk of invasion or transition to a more degraded state. There is a high level of variability of species in this state, which will shift in response to precipitation or in response to past management. The most representative community is discussed below.

Characteristics and indicators. Wyoming big sagebrush is a significant component (> 25%) of the plant community and the preferred mid-stature cool season grasses have been eliminated or greatly reduced. Sandberg bluegrass and western wheatgrass are prominant, but usually within the crown of sagebrush or prickly pear cactus. The interspaces have expanded, leaving significant bare ground.

Community 2.1
Wyoming Big Sagebrush/Bare Ground

This plant community is the result of frequent and severe grazing during the critical growing season and/or protection from fire. Sagebrush dominates this plant community, with the annual production of sagebrush exceeding 25%. Wyoming big sagebrush is a significant component of the plant community and the preferred mid-stature cool season grasses have been eliminated or greatly reduced. The dominant grasses are Sandberg bluegrass and western wheatgrass. Prickly pear cactus often increases. The interspaces between plants have expanded leaving the amount of bare ground more prevalent. When compared to the Reference Plant community 1.1, the total annual production is similar. However, the herbaceous production is markedly lower, with the shrub production absorbing the difference. This community is vulnerable to invasive weeds such as cheatgrass, knapweeds, or whitetop if a seed source is available. The total annual production (air-dry weight) of this state averages 500 pounds per acre, but it can range from 255 lbs./acre in unfavorable years to 850 lbs./acre in above average years.

Resilience management. This plant community is resistant to change as the sagebrush stand becomes more mature, but is at-risk due to its susceptibility to invasive species. This plant community may be more resistant to fire as fewer 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 cool-season grasses. Plant litter is noticeably less when compared to the Reference Plant Community. Soil erosion is accelerated because of increased bare ground. Water flow patterns and pedestalling are obvious. Infiltration is reduced and runoff is increased. Rill channels may be noticeable in the interspaces and gullies may be establishing where rills have concentrated down slope.

State 3
Sod-Formers

Figure 16. Blue grama taking over the understory of Wyoming big sagebrush and prickly pear cactus.

The degraded condition of this State is driven by the loss of hydrologic function and species diversity with the increase of sod-forming grasses, mainly blue grama with a smaller component of threadleaf sedge. This site is the result of long-term season long grazing by large ungulates; but long term exclosures also suggest a possible response or impact of shifts in historic weather patterns.

Characteristics and indicators. The dominant sod-forming grass that currently exists within this LRU is blue grama with intermixed areas of threadleaf sedge. Both are species that persist as a component of the perennial vegetation naturally (in reference communities) within this ecological site. The general tendency is for these species to increase with prolonged drought or under grazing pressure, becoming dominant. Hydrology of the site is altered by increased surface runoff from the dense shallow root system that inhibits the movement of water through the soil. The sod patches will direct surface flow around the edge of the mat concentrating flow into channel like patterns, creating a difficult or harsh environment for native grass species and forbs to persist.

Community 3.1
Sod-Former/Sagebrush

Figure 17. Blue grama dominated community.

This plant community is the result of continuous season-long grazing, repeated severe grazing, or prolonged drought. Improper grazing practices have adversely affected the perennial grasses and shrub component creating an open canopy that allows the mat forming plants to expand. The natural effect of blue grama and threadleaf sedge, with their short-stature dense root structure, is a decrease of water infiltration. This decrease in infiltration expands channelization of runoff between vegetation patches. The lack of structure to hold moisture and continued drought will continue to reduce the shrub component. A dense sod of blue grama with patches of threadleaf sedge is the major grass component remaining in this community. Minor occurrences of other perennial natives are incidental within the sagebrush canopy and/or prickly pear cactus. Wyoming big sagebrush has been reduced in vigor and cover across this site. However, it will persist in small patches of 3-5% cover on the landscape. When compared to the Reference Plant Communities 1.1 and 1.2, blue grama has increased significantly, making up 30 to 60% of the canopy. Prickly pear cactus has invaded the site, and other cool-season mid-stature 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 325 pounds per acre, but it can range from about 180 lbs./acre in unfavorable years to about 575 lbs./acre in above average years.

Resilience management. This community is at-risk of transitioning to a completely sod-bound community without woody vegetation. The dense root mats are extremely resistant to change. Continued frequent or severe grazing or the removal of grazing does not seem to affect the plant composition or structure. The shrub component will decline and eventually be removed from the plant community under either scenario. The biotic integrity of this state is nonfunctional and plant diversity is extremely low. The plant vigor is reduced and replacement capabilities are limited due to the few remaining cool-season grasses. This sod-bound plant community is very resistant to water infiltration. While the sod protects the site itself, off-site areas are affected by increased runoff that can cause rills and gully erosion. Water flow patterns are obvious in areas of bare ground and pedestalling is apparent along the sod edges. Rill channels are noticeable in the interspaces and down slope. The watershed may or may not be functioning, as the increased runoff may affect adjoining sites. This community has the ability to improve, but not recover to reference, with management and mechanical manipulation. Once the sagebrush component has been lost, however, recovery or transition is not as feasible. This community is considered to be “at-risk”. The potential to shift into the more degraded and stable state of a Sod/Cactus community is higher than the potential to improve. The threshold composition of sod-forming grasses and the lack of significant cover by other perennial grasses makes these two communities (3.1 and 3.2) very similar. The shift in sagebrush and cactus cover are the defining characteristics.

Community 3.2
Sod/Prickly Pear Cactus

Figure 19. Blue grama and prickly pear cactus dominated community.

Transitioning from the Sod/Sagebrush community phase (3.1) to the Sod/Cactus community phase (3.2) may occur as a slow and steady process from the initial transition into a sod-former state through drought or continued pressure on the remaining shrubs. A dense sod of blue grama with threadleaf sedge intermixed, is dominant with increasing prickly pear cactus in the community. Cactus density has the potential to increase to a level that inhibits the ability for livestock to move through or graze the available forage. Wyoming big sagebrush has been generally removed from the community with only isolated occurrences. Rubber rabbitbrush is significantly reduced, but persists on the landscape. When compared to the Reference State (1.1 and 1.2), blue grama and prickly pear cactus have increased. All cool-season mid-stature grasses, forbs, and most shrubs have been greatly reduced or removed. Production has been significantly decreased. The ability for upland sedges, as well as remnant species such as Sandberg bluegrass, to respond to spring moisture allows for a significant range in production. Study plots have documented a range in production of less than 160 pounds one year to over 500 pounds the next year with no change in density/frequency, based only on timing and amount of precipitation. So production is provided as an average or median number and is not intended to cover the full range of production potential for this community. The total annual production (air-dry weight) of this state is 285 pounds per acre, but it can range from 160 lbs./acre in unfavorable years to 500 lbs./acre in above average years.

Resilience management. This sod bound community is extremely resistant to change and continued frequent and severe grazing or the removal of grazing does not seem to affect the plant composition or structure of the plant community. The biotic integrity of this state is not functional, plant diversity is extremely low, vigor is significantly weakened, and replacement capabilities are limited due to the reduced number of cool-season grasses. The dense root mat of this community is resistant to water infiltration, but is able to utilize the water captured by the root zone. However, off-site areas are affected by excessive runoff that can cause rills and gully erosion. Water flow patterns are obvious within the bare ground (interspaces) and pedestalling is apparent along the sod edges. Rill channels are noticeable in the interspaces and down slope. The watershed may or may not be functioning, as runoff may affect adjoining sites.

Pathway CP 3.1-3.2
Community 3.1 to 3.2

Sod-Former/Sagebrush

Sod/Prickly Pear Cactus

Intensive Brush Management, Fire, Frequent or Severe Grazing, Drought – In a sod dominant community, the hydrology has been altered drying the soils and reducing the potential for seedling establishment by many native grasses and shrubs. Once sagebrush is removed from this community by intense grazing pressure, drought and insect damage or by fire (rare), wild or prescribed, the community will phase into a sod and cactus dominated community. The Wyoming big sagebrush component of this community is the at risk species. Drought alone, or with grazing pressure through season or yearlong patterns, will weaken the sagebrush canopy. The sod-dominated community reduces the ability for sagebrush to propagate, also leading to a recession of sagebrush. Fire has little influence on this community due to the lack of fine fuels to carry it. In rare circumstances, isolated areas may burn within the shrub canopy. In some cases, rubber rabbitbrush will persist or increase slightly on a site as sagebrush diminishes. It is also noted that with periods of drought there is a marked decrease in the health and vigor of threadleaf sedge and blue grama; weakening the sod, and creating a thinning or dieback of the sod.

State 4
Invaded

Cheatgrass or downy brome (Bromus tectorum) is the invader that has the greatest concern for most land managers. This invader has an aggressive growth habit that creates a harsh environment for most native species, including sagebrush. Multiple growth cycles throughout a year leaves a thick litter (duff) layer and builds a significant seedbank. The ability to persist through the winter under snow and sprout early gives it the advantage over native species for the early spring precipitation and snowmelt. Shifts in climatic patterns, 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 threat most prevalent to rangelands on a large scale, a variety of thistles, knapweeds (spotted, Russian, etc.), and whitetop (hoary cress) are increasing in density and frequency, creating their own set of challenging management issues. As more or new invasive species are found or identified within the Wind River Basin, the community dynamics in this state will continue to shift in response to the species-specific concerns.

Characteristics and indicators. This state is characterized by the presence of an invasive/non-native species. Extended periods of drought alone; or in combination with severe grazing, insect damage, or wildfire has weakened the native composition of the community opening the canopy for invasion. The competitive nature of annuals and other invasive species, the loss of diversity, changes to the potential of a site due to allelopathy or other deterrent characteristics of invasive species, and risks or limitations associated with the various invasive species creates a hostile environment for both native species and grazers.

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

Community 4.1
Native/Invasive/Sagebrush

The Perennial Grasses/Invasive Species/Wyoming big sagebrush community phase (4.1) has maintained a representative range of native perennial grasses and forbs that are key to this particular ecological site with the accompanying Wyoming big sagebrush component. Although this community phase is very susceptible to becoming an invader driven system. If native grasses can maintain at least a 50% composition; there is still a chance that the community can be improved. However, the high costs required for improvement will limit the economic feasibility of treatment. This community phase is characterized by a significant presence of invasive species composition (5% or greater) on the landscape, and are prominent on the site (referring to a more wide scale composition, not one small patch in an isolated portion of the landscape). The litter or duff layer created by many of the known invasive species, but specifically cheatgrass, is significantly higher than the native community. This duff layer creates a barrier that can impede water infiltration and increase runoff, which accelerates erosion. This is exacerbated with increased slope. The duff layer creates an extreme hot zone during wildfires that can sterilize the soil through volatilization of needed nutrients or by the formation of an ash cap that seals the soils. This cap prevents water infiltration and seed penetration and reduces the ability for re-vegetation post-disturbance. Production of the perennial grasses and forbs is reduced. However, the total production will maintain or may be slightly higher due to the overall biomass and expanded growth potential of many of the annual/invasive species. A specific production range is not provided due to the variability of composition that will effect overall production.

Resilience management. This plant community is prone to fire in response to the increase in fine fuels from the added biomass (litter) produced by the invaders. Plant diversity is moderate for this phase because the native perennials and woody shrubs have maintained their position within the community. The plant vigor can be variable and is generally only slightly diminished at this stage. However, replacement capabilities are limited due to the added competition for moisture and nutrients available after cheatgrass has sprouted. Plant litter is noticeably higher when compared to reference communities. However, the potential biomass produced is dependent on the invasive species. Soil erosion is variable depending on the species and their associated litter accumulation. This variability also applies to water flow patterns and pedestalling. Infiltration is unaltered or slightly reduced. However, as the duff layer and litter build, infiltration will decrease and runoff will increase.

Community 4.2
Invasives/Sagebrush

As the native populations of perennial grasses and forbs are lost from severe grazing or other 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 transitioning to Community Phase 4.3. At this point, from hydrologic and biotic standpoints it will become irreversible without complete reclamation, which makes this community phase, the At-Risk community. Wyoming big sagebrush is able to compete and maintain a strong community under a heavy influx level of most invasive species, unless fire or similar disturbance removes the woody cover. The canopy of the sagebrush provides a protected position in the system for native grasses and forbs, allowing remnant populations to persist. However, the system is low in resistance and even lower in resilience. The fine fuels or biomass produced by most invasive species, with the most obvious being cheatgrass, make fire a significant threat and frequent occurrence. Strategies to control or manage for invasive species, namely cheatgrass, are being researched across the western United States. High intensity grazing with chemical control and the use of biological agents are techniques that have been tested, with varying levels of success. The key management strategy needs to maintain the remnant populations of native grasses, by reducing the risk of fire. This approach will allow Wyoming big sagebrush to persist. This strategy will also maintain the biotic integrity by maintaining species richness, which provides structure and a range of growth traits. This structure will provide adaptability of the site to varying climatic swings and help support the hydrologic function. Enhancing snow catchment and shade will allow a slow release of winter precipitation during spring melt. This will provide a longer moist season for optimal growth of native species). Each location will need to 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 site.

Resilience management. This plant community is resistant to change in relation to returning to a native dominated system. However, as the stand becomes more decadent, it loses its resistance to shift to an invader only community. These areas may be more prone to fire as fine fuels are more available and the bare ground between the sagebrush plants is reduced with increased biomass and plant density of the annual invaders. Plant diversity is poor. The plant vigor has declined and adaptability/replacement capabilities are limited due to the reduced number of cool-season grasses. Noticeably more plant litter is apparent when compared to reference communities. This is caused by the additional biomass produced by the invasive species (species dependent). Soil erosion is variable depending on the species of invasion and the associated litter accumulation. 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
Invasives

Downy brome, better known as cheatgrass (Bromus tectorum), is able to emerge and grow late into the fall and green up in early spring before snowmelt. This early and late growth pattern allows cheatgrass to utilize fall and spring resources that are otherwise stored for the dormant native cool season perennial vegetation. Seeds are able to persist for long periods, allowing propagation beyond the life span of the native seed source. This plant out-competes native and many improved varieties of grasses because of its ability to quickly utilize minimal available resources, produce large quantities of seed quickly, and reproduce in poor conditions. The morphology of the seed allows for easy dispersal and longevity creating a widespread and long-lived seed bank. These traits create a management challenge that has not been successfully overcome at this time. Once cheatgrass has established on a landscape, it is resistant and resilient to change. In this community, with the absence of sagebrush, there may be native species that will persist in small scattered populations or sparsely under the canopy of the cheatgrass. Certain climatic conditions will allow natives to show their resiliency and respond to the available resources (typically mid-spring moisture), but are generally unable to out-compete the annual invader, and remain suppressed in the community. The ability for cheatgrass to emerge, bolt, produce seed and mature out two to three times within a year utilizes all available soil nutrients and moisture resources. Chemical control is difficult to attain and maintain success without lasting effects on the native grasses in the area. Chlorosis of wheatgrasses, stunted plants, and loss of certain forbs are a few of the residual chemical effects (The herbicide, Plateau, has been widely used in this region.) These effects generally come from the chemical composition and its ability to bind to the chemistry or nutrients in the soil inhibiting the uptake by roots. The extensive fine fuel load created by cheatgrass increases the fire frequency interval to an average of five years. This shorter cycle prevents sagebrush and other woody species from establishing on the site. A five-year cycle has negative impacts on many of the native herbaceous species in the understory, increasing evaporation, mineralization and vaporization of many of the nutrients, which depletes the soil. 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 may be avoided. However, light grazing through the middle of the growing season is difficult, and defeats the purpose of intensively grazing the location. On smaller, invaded sites or under certain conditions, targeted 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 from loss of cool-season grasses. Plant litter is noticeably higher 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 has been lost in this community.

Pathway CP 4.1-4.2
Community 4.1 to 4.2

Frequent or Severe Grazing, Wildfire, Drought – Drought, wildfire, or other climatic stresses on the system will continue to hinder the native species, reducing their ability to maintain their position in the plant community. This continued stress combined with frequent or severe grazing pressure from wildlife and livestock can reduce the native composition to an unviable or unsustainable population. At this point, the invasive species will become dominant. The fleshy growth of native species are generally preferred over the thin straw like growth of cheatgrass. During initial spring green up while natives are still dormant, wildlife and cattle will utilize the cheatgrass. However, once the native species begin to green up, the animals will switch back to their preferred species. Inaction by the land manager will also aid in the transitioning to phase 4.2.

Pathway CP 4.1-4.3
Community 4.1 to 4.3

Fire, Drought, Ground Disturbance, Severe Grazing – Once the presence of invasive species occurs, stress or ground disturbance of any means coupled with the lack of management of the invader, allows the invasive species to occupy and dominate the site. The stressors that most commonly occur that remove the sagebrush and amplify the weed infestations are fire (wild/prescribed), drought, insect damage and disease, as well as frequent and severe grazing by large herbivores.

Pathway CP 4.2-4.1
Community 4.2 to 4.1

Integrated Pest Management/Weed Control and Long-term Prescribed Grazing - Control of invasive species and targeted grazing to utilize the invasive species with minimal impact to the native population, will allow the community to regain or maintain potential. However, at this phase it is not possible to eradicate the invasive species. Sustained control requires intensive inputs over the course of several years. To maintain the system with no further degradation requires a combined approach of both long-term prescribed grazing and intensive weed management (integrated pest management). No one single practice can sustain this phase. Maintaining this phase requires intensive management to prevent the transition to Phase 4.3 - Invaders/Annuals.

Pathway CP 4.2-4.3
Community 4.2 to 4.3

Fire, Drought, or Ground Disturbance with Severe Grazing - Once this community has been compromised by a substantial composition of invasive species, stress or ground disturbance of any means may cause the invasive species to occupy and dominate the site. Drought and related disease and insect damage will weaken and remove the remaining sagebrush canopy. Removal of this canopy leaves a near monoculture of invaders. Frequent and severe grazing by large herbivores is another impact that leads to this community. Management actions that reduce or damage the existing sagebrush canopy exposes the remaining native grass population and will start the transition. Drought or further disturbance or improperly timed grazing (grazing when the desired species are in the early boot growth stage or beginning to flower), will finish the transition.

State 5
Altered

The arid nature of this region has played a major role in the development and transitions in land use over time. Landscapes accessible by irrigation water and equipment were farmed and many were later abandoned and left to return to rangeland. Other landscapes were treated with a variety of practices to manage or eradicate sagebrush. Tillage of the soil, change in hydrology caused by the loss of vegetative structure, constant climatic fluctuations, and advancements in seed sources have created this altered state. Once a soil has been disturbed, whether it was mechanical, cultural, or natural the change in soil structure, hydrologic function, and possibly stability prevent a site from supporting the native vegetation or responding to management the same as the reference site. Reclamation or restoration of an area will not replace the original function and factors that made the original location respond as it did. So these "altered" lands may, after significant inputs and time, look similar to the Reference communities (1.1 or 1.2), but they will not be able to respond or function the same way as the Reference community. The disturbed or degraded state could be shown as a stand-alone box within the state and transition model diagram. No matter what state 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. Consideration of this state for an alternate ecological site would be reasonable. In some cases (site by site consideration), a re-correlation of a location may be the best solution. However, in many cases, the soils have not been altered beyond the current site characteristics. However, the potential has shifted enough that it is no longer truly comparable to the reference state. Tillage of a site, alters the soil structure, depletes the biota of the soil and dries the profile. The loss of soil structure changes the water holding capacity of the soil, and the mixing may remove argillic or clay bulges, which may increase the movement through the soil, and reduce the available water capacity. The time required for soil to recover and re-establish the healthy biota is highly variable depending on the climatic conditions following the event. The initial flush of weedy vegetation (kochia, Russian thistle, and mustards) is the initial step in the recovery process. Although they are only successional species, they provide organic material, nutrient flow and erosional protection. However, they lack the perennial structure and root system to fully stabilize the site. When the seeded area establishes, the site may become similar in composition to reference. However, the integrity of the soil has been altered, changing potential of the site. A dynamic state was depicted to detail the altered communities that exist on the landscape.

Characteristics and indicators. Soil disturbances, indications of seeding (rows, presence of strong stands of improved grass species or selective seeded species - crested wheatgrass, Russian wildrye, etc.), or the prominent cover of early successional plants (kochia, russian thistle, mustards) are strong indicators or characteristics of a disturbed/degraded or altered landscape.

Community 5.1
Disturbed/Degraded lands

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 patch or wider disturbances, such as well pads or parking areas. Small scale or isolated disturbances (spot fires, prairie dog towns) 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 on the successional or seeded species that are able to establish in an area. On locations that were seeded with non-native species, the growth curve will vary from the native community. However, in the case of an early successional community, the growth curve may be similar. For a more accurate growth curve, a site-specific species inventory and documentation of the climatic trends should be collected.

Resilience management. The plant community is variable and depending on the age of the stand and the stage of succession, that the location is in will determine community resiliency. Plant diversity of these successional communities is generally strong, but is usually lacking in the structural groups that are desired on the site. In areas of new or frequent disturbance, annual weedy species or early successional plants will be the dominant cover, providing a strong diversity, but having minimal structural cover for some wildlife. As the site matures or as the period between disturbances is lengthened, perennial or taller statured, stronger rooted species will increase. By providing protection and improvement to the hydrologic process, these perennial species allow for other grasses and shrubs to begin to establish. This flexibility within the community creates a variable level of biotic integrity. Soil erosion is dependent on the disturbance regime and the biotic integrity of the community. The variability of the community also affects the water flow, infiltration, runoff, and pedestalling risk. Other factors that are more prevalent or influential for these sites are surface roughness and brokenness (tire tracks, hoof action, smoothed, denuded surfaces, or trails that may concentrate water flow).

Community 5.2
Restored/Reclaimed

Shifts in reclamation practices over the last several decades have altered the success and stability of reclaiming a site. Crested wheatgrass was a species used frequently for reclamation throughout Wyoming. Across the state, many of these communities persist today. These stands are stable and generally persist as a monoculture until a disturbance creates a niche for native species to establish. Crested wheatgrass has spread into native communities as readily as native species are persisting within crested wheatgrass stands. Russian wildrye and varieties of rhizomatous and bunch-wheatgrasses are used in mixes to help increase establishment on these sites. The success of vegetative seeding trials are low to moderate in this LRU due to variable amounts and timing of precipitation events. However, seeding has succeeded in limited areas along pipeline corridors, well sites or pad sites, and along transportation corridors. Current interpretations of reclaimed or restored refers to the establishment of native species in a composition as close to a natural (pre-disturbance) plant community as possible. This excludes the use of non-native species, allowing a similar ecological response to the reference state. Although, to clarify, even when native species are used in reclamation, these plantings will not replicate the reference community in response to management due to the change in soil dynamics with mechanical disturbance (seedbed preparation and seeding), but they may be similar. The 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. Seeding mixtures will determine the plant community's resistance to change and resilience against the threat of invasive species and to erosion. Many plantings are diversity poor, but are better than the monocultures that were seeded historically. Many seeded sites may be prone to fire because of the increased production potential and basal cover of species (seeding density) as they mature (more biomass and possibly more litter) providing abundant fine fuels to carry a fire. Soil erosion is variable depending on the establishment of the seeding, how it is seeded, and mechanical procedures put in place. The variability of the water flow and pedestalling as well as infiltration and runoff is determined again by the species that comprise the community and the method of seeding (site preparation and seeding practice). The challenge to establish shrubby species to the density they were pre-disturbance, and the general difficulty to reseed sagebrush, has limited the recovery of the hydrologic cycle.

Pathway CP 5.1-5.2
Community 5.1 to 5.2

Seeding, Brush Management, Integrated Pest Management, Prescribed Grazing Management – With proper mechanical improvements and follow-up maintenance, a disturbed site can be improved and utilized for an intended purpose. However, climatic limitations affect the success of re-seeding. Depending on the location, seeding plots are slow to establish and invasive species are a risk, creating a moderately low success potential. Proper preparation of a location to be seeded or once a site is seeded, integrated pest management becomes crucial to allow seedling establishment and to prevent invasive species from invading the area. Brush management may be required for open areas that can readily be seeded.

Pathway CP 5.2-5.1
Community 5.2 to 5.1

No use, No Fire, Long Term Prescribed Grazing, Frequent or Severe Grazing - In general, if a site is not maintained with the conditions of which the species are adapted under, a decline in vigor and a corresponding shift in composition will occur. Since the soils are altered from reference state due to plowing, mining, or other similar disturbances, the plant community will not follow the same expected shifts as the native community. Monitoring and recording range trend over time is needed to determine if a location is degrading or adjusting with the climatic variables of the site. The initial establishment phase of a reclaimed site is crucial to determine success, but at any stage of a seeding, degradation or further disturbance can occur forcing the site to phase back to the disturbed community.

Transition T 1-2
State 1 to 2

Rhizomatous Wheatgrass/Sagebrush

Sagebrush/Bare Ground

Frequent and Severe Grazing (Year-long) or Drought - Frequent or high intensity herbivory weakens the ability for the grasses to persist, especially during prolonged drought. The weakened herbaceous component in combination with lack of fire provides the opportunity for sagebrush to become dominant. Over time, the sagebrush density and lack of understory will prevent recovery without intervention. The conversion to a Wyoming Big Sagebrush/Bare Ground State is a response to extended periods of stress, both climate and/or human induced. Intensive grazing with minimal to no recovery period begins the transition, and with added climatic stress, species diversity and productivity is lost, and the community crosses into the Sagebrush/Bare ground State. The illusion of crossing the threshold to State 2 can be found during non-typical precipitation years for communities dominant in needleandthread. The loss of species density and diversity, increased bare ground and decreased litter are the indicators that a true transition has occurred.

Constraints to recovery. Lack of seed source is the only major constraint for recovery of this community.

Transition T 1-3
State 1 to 3

Rhizomatous Wheatgrass/Sagebrush

Sod-Formers

Frequent Grazing (Yearlong), Brush Management or Fire with Drought – Severe and frequent grazing reduces vigor and abundance of key species. As rhizomatous wheatgrasses, and needleandthread decline, short-statured grasses become dominant. Long duration, high intensity herbivory reduces the mid-stature bunchgrasses through repeated defoliation as well as physical damage to the crown and growth points of the plants. The open canopy and soil condition encourages species that are tolerant to heavy trampling and frequent defoliation. These species are generally the mat or sod-forming species of blue grama and threadleaf sedge. Prolonged drought or climatic stress may also encourage the sod-formers to fill in the interspaces. The shallow, dense root mats will continue to spread over time.

Constraints to recovery. The persistence and resilience of the root mat formed by sod-forming species as well as the alteration to hydrology make the recovery process unfeasible.

Restoration pathway R 2-1
State 2 to 1

Sagebrush/Bare Ground

Rhizomatous Wheatgrass/Sagebrush

Prescribed Grazing with Brush Management or Wildfire - Treatment to thin the canopy to allow the native vegetation to respond to improved moisture and sunlight followed by prescribed grazing to prevent overuse of the exposed grasses will help this community recover. Treatment will vary depending on the specific 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. Post treatment grazing management is critical for successful long-term recovery. 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. Weather and treatment conditions during and following a wildfire will also influence the community. Prior to treatment, carefully checking the immediate and surrounding area will help ensure little or no invasive species (cheatgrass) is present.

Transition T 2-3
State 2 to 3

Sagebrush/Bare Ground

Sod-Formers

Drought, Disease, Insect Damage, Severe Grazing, or Fire - Sod-forming species such as blue grama and threadleaf sedge are able to tolerate high levels of grazing use and will maintain as other native species decline. Hoof action or compaction inhibits more desirable native species, allowing the sod-formers to become more dominant on the landscape. This decline creates a sagebrush / sod-former community that is resistant to change with grazing management. Impacts to sagebrush by disease or insect damage, as well as drought or herbivory, will shift state 2 to the secondary community phase with cactus as a subdominant species with blue grama.

Constraints to recovery. Compaction, altered hydrology, and the lack of seed-source are the major constraints for this site to recover. The ability to reduce the dense root-mat of a sod-former inhibits the transition back to bare ground scenario.

Transition T 2-4
State 2 to 4

Fire (wild), Frequent or Severe Grazing, Drought with Insect Damage or Brush Management – Throughout most of this LRU there is a seed source present in the soil for cheatgrass, knapweed, and other invasive species. Stress to the native plant community creates a niche for invasion by undesirable or weedy species. Several causes of stress include drought, wildfire, prescribed burning and other forms of brush management, ground and soil disturbance from intensive grazing by large herbivores, or recreational activities. Documentation has shown that often the invasion starts with one or two isolated plants. If these plants can be treated early, a full infestation of the site can be avoided. However, if these plants are undetected, ignored, or further stress or disturbance occurs, the population soon grows exponentially. In some cases the invasive species, once established, can create its own habitat, forcing the weaker native species out. The open canopy of the Sagebrush/Bare Ground State is vulnerable to invasive species without further influence. With continued over-use, drought, insect damage or fire, 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 cool-season native grasses, allowing them to persist on the landscape.

Constraints to recovery. The ability to recover and remain in this degraded state, is the lack of vegetation. The significance of the bare ground in State 2 is prone to or encourages invasion by non-native or aggressive species. To remove these species and then maintain their removal is difficult without shifting the community to another state completely. (State 1,3, or 5). The second constraint is the ability to control the invasive weed without the thought to susceptibility. Cheatgrass has not been successfully eradicated from a community, rendering a recovery back to state 2 impossible at this time.

Transition T 3-4
State 3 to 4

Frequent and Severe Grazing, Drought, Disturbance with a seed source present - The chance of wildfire is reduced with the loss of fine fuels and reduced sagebrush canopy. Increased pressure from severe grazing and drought combine to weaken the sod or mat-like community of low stature grasses, making the site vulnerable. Continued disturbance opens the bare ground or interspaces to annuals and other 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, it is extremely difficult to manage and may not be feasible to completely remove them from the community. Once the invasive species have become prevalent (>5% composition) on the landscape, the community crosses the threshold into the Invaded/Sagebrush State (State 4).

Constraints to recovery. The only significant constraint to recovery, is the ability to remove/eradicate the noxious weed/invasive weed that has invaded the community.

Restoration pathway R 4-5
State 4 to 5

Integrated Pest Management, with seeding - Integrated pest management plan or intense weed control after and possibly before seedbed preparation will be necessary to overcome a severe weed infestation. Preparing a seedbed (tilling) and using either improved varieties, native seed, or in some cases, an introduced species suited for the management use intended may be the only way to overcome some invasive species. Success of re-establishing a native or desired plant community on a large scale has not been documented. Small-scale attempts are rated to be low and highly variable for the rate of control of most species. Possibly, a site could be established to look similar to an at-risk community within the reference state. However, it is still not possible to reach the reference community condition once annuals have established on a site. The need to till the soil or to prepare the seedbed for planting the native species, 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 soils, the change in the plant community and the risk of re-invasion of the site will prevent it from reacting in the same manner to management and environmental changes as an unaltered native community. Therefore, it remains in the reclaimed state/community phase 5.2.

Transition T 5-4
State 5 to 4

No Use, Fire (wild or prescribed), Frequent or severe Grazing, Drought with Seed Source Present – In the reclamation or restoration process, or after a land disturbance occurs, if no management is put into place to prevent a reoccurrence or a new infestation of weeds, the community will revert back or transition to an invaded state. Wildfire, prescribed burning, drought, or frequent and severe grazing by large herbivores can be a source of the disturbance that either opens the canopy and/or introduces the species to the location. Extended periods of non-use creates a decadent community with a large proportion of dead growth persisting around the crown of the plants, reducing vigor and production. As the plants begin to dieback, the community becomes vulnerable to weed invasions. The reverse of the non-use scenario, it has been found that frequent or severe grazing, drought, or fire can open the canopy to invasion as well. This invasion triggers the transition to an invaded state.

Context dependence. The disturbance of cause of the infestation and the seed sources that are available/introduced are the driving factors for the specifics of this transition.