State 1
Reference

The Reference state of this ecological site consists of two known potential plant communities, the Bluebunch community and the Mixed Bunchgrass community. These are described below but are generally characterized by a mid-statured, cool season grass community with limited shrub production. The Bluebunch community is dominated by bluebunch wheatgrass and is considered the reference, while Community 1.2 has a codominance of bluebunch, needle and thread, and western wheatgrass with an increase in forbs and Wyoming big sagebrush.

Community 1.1
Bluebunch

In this community, bluebunch wheatgrass (Pseudoroegneria spicata), green needlegrass (Nassella viridula), and needle and thread (Hesperostipa comata) are dominant. Shrub species (big sagebrush, prairie sagewort, and broom snakeweed) remain a subdominant component of this site. Sandberg bluegrass (Poa secunda) and dryland sedges are also common. This state is in areas with proper livestock grazing or little grazing pressure. Bluebunch wheatgrass lacks resistance to grazing during the critical growing season (spring). It will decline in vigor and production if grazed in the critical growing season for more than one year in three (Wilson et al., 1960). The Bluebunch community is moderately resilient. It will return to dynamic equilibrium following a relatively short period of stress (such as drought or short-term improper grazing), provided a return of favorable or normal growing conditions and properly managed grazing.

As discussed in the Ecological Dynamics section, the natural fire regime restricted shrubs in this Bluebunch community. Shrub species may include Wyoming big sagebrush, winterfat, tarragon (Artemisia dracunculus), and prairie sagewort (Artemisia frigida). Infrequent fire maintained big sagebrush communities as open, seral stands of productive herbaceous species with patches of big sagebrush.

Resilience management. Prescribed grazing; prescribed burning; brush management; pest management.

Community 1.2
Mixed Bunchgrass

Western wheatgrass tolerates grazing pressure better than bluebunch wheatgrass and green needlegrass. The growing point for bluebunch wheatgrass grass is several inches above the ground, making it very susceptible to continued close grazing (Smoliack et al., 2006), while western wheatgrass growing points tend to be near the plant base. Western wheatgrass and Sandberg bluegrass increase in species composition when more palatable and less grazing-tolerant plants decrease from improper grazing management. Western wheatgrass and bluebunch wheatgrass share dominance in the Mixed Bunchgrass community, with green needlegrass subdominant. Other grazing-tolerant grass species are likely to increase in number compared to the Bluebunch community, including Sandberg bluegrass (Poa secunda), prairie Junegrass, and blue grama (Bouteloua gracilis). Western yarrow (Achillea millefolium var. occidentalis), spiny phlox (Phlox hoodii), scarlet globemallow (Sphaeralcea coccinea), hairy false goldenaster (Heterotheca villosa), and pussytoes (Antennaria spp.) are examples of increaser forbs. Prairie sagewort (Artemisia frigida) is a shrub that increases under prolonged drought or heavy grazing and can respond to precipitation in July and August.

Heavy, continuous grazing will reduce plant cover, litter, and mulch. The timing of grazing is important on this site because of the moisture limitations beyond June, especially on the drier sites. The bare ground will increase, exposing the soil to erosion. Litter and mulch will be reduced as plant cover declines. If bluebunch wheatgrass remains a dominant species in total biomass production, the site can return to the Bluebunch community (Pathway 1.2a) under proper grazing management and favorable growing conditions.

Western wheatgrass will continue to increase until it makes up the majority of the species composition. It may be difficult for the site to recover to the Bluebunch community once bluebunch wheatgrass has been reduced to less than 15 percent by weight. The risk of soil erosion increases when canopy cover decreases. As soil conditions degrade, there will be a loss of organic matter, reduced litter, and reduced soil fertility. Degraded soil conditions increase the difficulty of reestablishing bluebunch wheatgrass and returning to the Bluebunch community.

The Mixed Bunchgrass community is the at-risk plant community for this ecological site. When overgrazing continues, increaser species such as needle and thread and native forb species will become more dominant, and this triggers the change to the Altered state or the Degraded state. Until the Mixed Bunchgrass community crosses the threshold into the Mixed Grass and Shrubland community or the Invaded community, community 1.2 can be managed toward the Bluebunch community using prescribed grazing and strategic weed control. It may take several years to achieve this recovery, depending on growing conditions, the vigor of remnant bluebunch wheatgrass plants, and the aggressiveness of the weed treatments.

Resilience management. Prescribed Grazing; brush management; pest management; prescribed fire.

Pathway 1.1a
Community 1.1 to 1.2

Bluebunch wheatgrass loses vigor with improper grazing or extended drought. When vigor declines enough for plants to die or become smaller, species with higher grazing tolerance, such as needle and thread, increase in vigor and production as they access the resources previously used by bluebunch wheatgrass. The decrease in species composition by weight of bluebunch wheatgrass to less than 50 percent indicates that the plant community has shifted to the Mixed Bunchgrass community. The driver for community shift 1.1a is improper grazing management or prolonged drought. This shift is triggered by the loss of vigor of bluebunch wheatgrass, soil erosion, or prolonged drought coupled with improper grazing. Drought and warmer than average temperatures are known to advance plant phenology by as much as one month (Blaisdell, 1958). During drought years, plants may be especially sensitive or in a critical stage of development earlier than expected.

Pathway 1.2a
Community 1.2 to 1.1

The Mixed Bunchgrass community (1.1.2) will return to the Bluebunch community (1.1.1) with proper grazing management and appropriate grazing intensity. Favorable moisture conditions will facilitate or accelerate this transition. It may take several years of favorable conditions for the community to transition back to a bluebunch-dominated community. The driver for this community shift (1.2a) is the increased vigor of bluebunch wheatgrass, representing more than 50 percent of the species composition. The trigger for this shift is the change in grazing management favoring bluebunch wheatgrass. In general, these triggers include conservative grazing management styles such as deferred or rest rotations utilizing moderate grazing (less than 50 percent grazing use) coupled with favorable growing conditions like cool, wet springs. These systems tend to promote increases in soil organic matter, which supports microfauna and can increase infiltration rates. Inversely, long periods of rest when this state is considered stable may not increase bluebunch wheatgrass. It has been suggested that these long periods of rest or underutilization may drive the system to a lower level of stability by creating large amounts of standing biomass, dead plant caudex centers, and gaps in the plant canopy (Noy-Meir, 1973).

State 2
Altered

This state is characterized by having less than 15 percent bluebunch wheatgrass by dry weight. This state is represented by two communities that differ in the percent composition of needle and thread, production, and soil degradation. Production in this state can be similar to that in the Reference state. Some native plants increase with prolonged drought, heavy grazing practices, or both. These species may include western wheatgrass, needle and thread, Sandberg bluegrass, scarlet globemallow, hairy false goldenaster, and prairie sagewort.

Characteristics and indicators. Less than 15 percent bluebunch wheatgrass; increase in short stature grasses; increase in bare ground.

Resilience management. Conservative grazing management; integrated pest management; time.

Community 2.1
Mixed Grass and Shrubland

Long-term grazing mismanagement with continuous growing-season pressure will reduce the total productivity of the site and lead to an increase in bare ground. Suppression of fire can also promote shrub growth, increasing plant interspaces. Once plant cover is reduced, the site is more susceptible to erosion and degradation of soil properties. Soil erosion or reduced soil fertility will result in reduced plant production. This soil erosion or loss of soil fertility indicates the transition to the Altered state because it creates a threshold requiring energy input to return to the Reference state. Extended drought conditions may exacerbate the transition to the Mixed Grass and Shrubland community.

Western wheatgrass dominates the Mixed Grass and Shrubland community. Bluebunch wheatgrass makes up less than 15 percent of species composition by dry weight, and the remaining bluebunch wheatgrass plants tend to be scattered and low in vigor. Invasive and increaser species will become more common. Hairy false goldenaster, Missouri goldenrod (Solidago missouriensis), stonecrop (Sedum sp.), and yarrow are examples of increaser forbs. It is not uncommon for a minor component of invader species, such as dandelion and yellow salsify (Tragopogon dubius), to be present. The presence of invader species creates more competition for bluebunch wheatgrass and makes it difficult for bluebunch wheatgrass to respond quickly to a change in grazing management alone. Therefore, an input of energy is required for the community to return to the Reference state. Wind and water erosion may be eroding soil from the plant interspaces. Soil fertility is reduced, and soil surface erosion resistance has declined compared to the Reference state.

This community crossed a threshold compared to the Mixed Bunchgrass community due to soil erosion, vegetation composition, loss of soil fertility, or degradation of soil conditions. These factors result in a critical shift in the ecology of the site. The effects of soil erosion can alter the hydrology, soil chemistry, soil microorganisms, and soil structure to the point where intensive restoration is required to restore the site to another state or community. Changing grazing management alone cannot create sufficient improvement to restore the site within a reasonable time frame. A study stated that with decreased grazing pressure, a needle and thread and blue grama plant community did not change species composition, but the content of the soil carbon increased (Dormaar et al., 1997). It will require considerable energy to move the site back to the Reference state. This state has lost soil or vegetation attributes to the point that recovery to the Reference state will require reclamation efforts, i.e., soil rebuilding, intensive mechanical treatments, reseeding, or all reclamation efforts.

The transition to this state could result from overgrazing and fire suppression, especially repeated early-season grazing coupled with extensive drought. If heavy grazing continues, plant cover, litter, and mulch will continue to decrease, and bare ground will increase, exposing the soil to accelerated erosion. Litter and mulch will move off-site as plant cover declines. The Mixed Grass and Shrubland community will then shift to a Shortgrass and Shrub community. Continued improper grazing will drive the community to a Degraded state. The introduction or expansion of invasive species will further transition the plant community into the Invaded state.

Community 2.2
Shortgrass and Shrubland

With continued mismanagement of grazing, especially with prolonged drought, mid-statured bunchgrasses will decline in production as plants become smaller. Species with higher grazing tolerance (such as western wheatgrass and prairie Junegrass) increase in vigor and production as they respond to resources previously used by the bunchgrasses. These less desirable, shallow-rooted species will become co-dominant with the bunchgrasses. Shrubs will become more competitive for limited moisture as bare ground and soil erosion increase. This community may exhibit conditions where livestock are consuming shrubs.

Pathway 2.1a
Community 2.1 to 2.2

The driver for community Pathway shift 2.1a is continued improper grazing management. This shift is triggered by the continued loss of bunchgrass vigor, especially needle and thread. The short-statured grasses will become more competitive and will become co-dominant with the bunchgrasses. Shrubs will increase in canopy cover; however, they may be browsed, resulting in spreading formations.

Pathway 2.2a
Community 2.2 to 2.1

If proper grazing management is implemented, western wheatgrass and bluebunch wheatgrass may regain their vigor and move toward the Mixed Grass and Shrubland community. Increased bunchgrass vigor will give grasses an advantage over invading shrubs. The advantage to grasses comes from following a conservative grazing plan where utilization is reduced, and rest or deferment is incorporated since the transition from community 2.1 to community 2.2 is likely caused by repeated heavy utilization. A study found that forage production increased by an average of 35 percent on western ranges when converting heavy to moderate utilization (Wambolt and Payne, 1986). Shrub removal and favorable growing conditions can accelerate this process. If the site contains Wyoming big sagebrush (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=ARTR2" target="_blank" title="Open in plants.usda.gov"><i>Artemisia tridentata</i></a> ssp. wyomingensis), low-intensity fire or mechanical treatment could reduce shrub competition and allow for increased vigor and the reestablishment of grass species (Wambolt and Payne, 1986; Personius et al., 1987).

State 3
Degraded

The Degraded state lacks mid-statured bunchgrasses. Western wheatgrass, blue grama, Sandberg bluegrass, and prairie Junegrass are dominant grasses. Broom snakeweed and prickly pear cactus have nearly replaced larger shrub species. Larger shrub species that remain are heavily hedged. This condition is likely a terminal state (e.g., restoration will likely be impossible or require major energy inputs beyond feasibility).

Characteristics and indicators. 25 to 50 percent bare ground, annual grasses, and cactus are common. Complete removal of bluebunch wheatgrass and green needlegrass. Replaced with Sandberg bluegrass, western wheatgrass, and blue grama. Sagebrush is hedged. Rabbitbrush and broom snakeweed remain un-browsed.

Resilience management. Prescribed grazing; range seeding; brush management; integrated pest management.

Community 3.1
Degraded Sprouting Shrub and Shortgrass

The Degraded Sprouting Shrub and Shortgrass community is dominated by short shrubs that sprout from animals browsing. Prairie sagewort, broom snakeweed, and rubber rabbitbrush are often dominant species, with shortgrass subdominant. Grasses often express a decumbent or prostrate growth habit. Needle and thread will have short leaves and express small basal areas. This site will have high bare ground and likely exhibit signs of erosion, with water flow patterns and pedestalling common, especially on steeper slopes. The complete removal of mid-statured bunchgrasses makes restoration nearly impossible. Reduced organic matter in the soil will hinder any restoration efforts.

State 4
Invaded

The Invaded state is identified as being in the exponential growth phase of invader abundance, where control is a priority. Dominance (or relative dominance) of noxious or invasive species reduces species diversity, forage production, wildlife habitat, and site protection. A level of 20 percent invasive species composition by dry weight indicates that a substantial energy input will be required to create a shift to the grassland state (herbicide, mechanical treatment), even with a return to proper grazing management or favorable growing conditions. Prescriptive grazing can be used to manage invasive species. In some instances, carefully targeted grazing (sometimes in combination with other treatments) can reduce or maintain the species composition of invasive species.

Characteristics and indicators. High amounts of invading species (both native and introduced).

Resilience management. Integrated pest management; prescribed grazing; brush management; prescribed fire; range seeding

Community 4.1
Invaded

Communities in this state may be structurally indistinguishable from the bunchgrass state except that invasive or noxious species exceed 10 percent of species composition by dry weight. This state may also include a community similar to the Degraded state, except that invasive or noxious species exceed 10 percent of species composition by dry weight. Although there is no research to document the level of 10 percent, this is estimated to be the point in the invasion process following the lag phase based on the interpretation of Masters and Sheley (2001). The threshold for aggressive invasive species (i.e., cheatgrass and spotted knapweed), could be significantly lower than 10 percent. Early in the invasion process, there is a lag phase where the invasive plant populations remain small and localized for long periods before expanding exponentially (Hobbs and Humphries, 1995).

Production in the invaded community may vary greatly. For example, a site with Kentucky bluegrass or spotted knapweed may have production near the reference community. A site with degraded soils and an infestation of cheatgrass may produce only 10 to 20 percent of the Reference state.

The Invaded state is reached when invasive species dominate the site, by species composition by weight, or their impact on the community. As invasive species such as spotted knapweed, cheatgrass, and leafy spurge become established, they become very difficult to eradicate. Therefore, considerable effort should be put into preventing plant communities from crossing a threshold into the Invaded state through early detection and proper management. Preventing new invasions is the most cost-effective control strategy and typically emphasizes education. Control measures used on the noxious plant species impacting this ecological site include chemical, biological, and cultural control methods. The best success has been found with an integrated pest management (IPM) strategy incorporating one or several options and education and prevention efforts (DiTomaso, 2000).

State 5
Cropland

Native rangeland has been converted for the production of forage crops or small grain products. This site often receives additional moisture from irrigation to increase production. Fertilizer and herbicides are frequently added to the Cultivated Cropland state to aid in crop production.

Community 5.1
Cultivated Forage

The Cultivated Forage community is the most common within the Cultivated Cropland State. It consists primarily of long-term grass, forb crops, or both planted for grazing or hay. If irrigation water is available, species will vary greatly depending on the land manager's goals and objectives but will almost certainly include alfalfa. Production from an irrigated site in this community is typically high. If irrigation is unavailable, the dry climate limits species options, which will likely include crested wheatgrass, Russian wildrye, or intermediate wheatgrass. Alfalfa is rarely a lone species under dryland conditions.

Community 5.2
Abandoned Cultivated Field

The Abandoned Cultivated Field community is a relatively rare occurrence due to the productive nature of this ecological site. However, as traditional land use transitions from agriculture to recreation, abandonment of cultivation may occur. If the site was in the Actively Cultivated community at the time of abandonment, the resulting plant community would likely transition into an herbaceous annual weed community. Over time, the weeds will typically yield a naturalized community of perennial grasses and forbs sourced from the surrounding plant community. Needle and thread, blue grama, Sandberg bluegrass, rabbitbrush, and prairie sagewort are the common native species that will colonize this site. Active Cultivated communities are rarely abandoned without some attempt to be planted in a Cultivated Forage community first. If the site was managed as a Cultivated Forage community at the time of abandonment, the plant community tends to transition into one that more closely resembles a Degraded state from the native rangeland condition. With enough time, native colonizing species will slowly fill the interspaces between the forage crops. Once the Abandoned Cultivated Field community has matured, it will have very similar ecological processes to the Degraded state.

Community 5.3
Active Cultivated

Active Cultivated community is common on this ecological site as the soil pH, water holding capacity, and inherent soil organic matter tend to favor annual cropping of small grains. If irrigation is available, this community can produce a wide variety of crops, including corn silage, pumpkins, sunflowers, and other specialty crops. The relatively short growing season tends to be the restriction if irrigation is used. Long-term annual cropping can destroy soil aggregation, create soil erosion (both wind and water), deplete organic matter, and alter pH, so a conservative crop management system will need to be applied to prevent site degradation.

Pathway 5.1a
Community 5.1 to 5.2

The Cultivated Forage community has been abandoned. This pathway occurs rarely in the present, but it has occurred in the past. This community can be observed in historically farmed areas that have been abandoned for unknown reasons. The field is left idle from crop management, and over time, the surrounding native vegetation fills the interspaces between plants.

Pathway 5.1b
Community 5.1 to 5.3

Cultivated Forage community is converted from permanent cover to an annually cropped system. Change takes place when cultivation or tillage occurs. This community pathway is frequent on this ecological site, particularly when the Cultivated Forage community’s production begins to drop. This often occurs on a 10 to 20 year cycle in this MLRA.

Pathway 5.2a
Community 5.2 to 5.1

Abandoned Cultivated Field is planted to a forage or hay crop of the manager’s preference. Often, this pathway will require tillage, herbicide, or both to terminate the existing plant community and seeding to initiate change.

Pathway 5.2b
Community 5.2 to 5.3

An abandoned cultivated field is converted to an annually cropped system. Change takes place when cultivation or tillage occurs. This community pathway is often necessary to convert a lower-producing or undesirable community into an annually cropped system.

Pathway 5.3a
Community 5.3 to 5.1

Active Cultivation community is planted to a forage or hay crop of the manager’s preference. This is a common pathway in the MLRA.

Pathway 5.3b
Community 5.3 to 5.2

Active Cultivated community is abandoned. This pathway is rare in the present, but it has occurred frequently in the past, which is how the Abandoned Cultivated Field community has been observed. The field is left idle from crop management. Over time, the surrounding native vegetation fills the interspaces between weedy, herbaceous plants.

Transition T1A
State 1 to 2

The Reference state transitions to the Altered state if bluebunch wheatgrass, by dry weight, decreases to below 15 percent or if bare ground cover increases significantly. The driver for this transition is the loss of taller bunchgrasses, which creates open areas in the plant canopy with bare soil. Soil erosion results in decreased soil fertility, driving transitions to the Altered state. Several other key factors signal the approach of transition T1A: increases in soil physical crusting, decreases in cover of cryptogamic crusts, decreases in soil surface aggregate stability, or evidence of erosion including water flow patterns, development of plant pedestals, and litter movement. The trigger for this transition is improper grazing management, long-term drought, or both, leading to a decrease in bluebunch wheatgrass composition to less than 15 percent and a reduction in total plant canopy cover.

Transition T1C
State 1 to 3

The Reference state transitions to the Degraded state when bluebunch wheatgrass is removed from the plant community and needle and thread is subdominant to short-statured bunchgrasses such as Sandberg bluegrass. The trigger for this transition is the loss of taller bunchgrasses, which creates open spaces with bare soil. Soil erosion results in decreased soil fertility, driving transitions to the Degraded state. Several other key factors signal the approach of transition T1C: increases in soil physical crusting, decreases in the cover of biological crusts, decreases in soil surface aggregate stability or evidence of erosion, including water flow patterns, the development of plant pedestals, and litter movement. The drivers for this transition are improper grazing management, intense or repeated fires, heavy human disturbance, or all three. Rapid transition is generally seen where livestock are confined to small pastures for long periods.

Transition T1B
State 1 to 4

Healthy plant communities are most resistant to invasion. However, regardless of grazing management, without some form of active weed management (chemical, mechanical, or biological control) and without prevention, the Reference state can transition to the Invaded state in the presence of aggressive invasive species such as spotted knapweed, leafy spurge, and cheatgrass. The Central Rocky Mountain Valleys tend to resist invasion by cheatgrass; however, repeated heavy grazing or intense human activities can open the interspaces of the bunchgrass community and allow for establishment. Long-term stress conditions for native species (overgrazing, drought, and fire) accelerate this transition. If populations of invasive species reach critical levels, the site transitions to the Invaded state. The trigger for this transition is the presence of aggressive invasive species. The species composition by dry weight of invasive species approaches 10 percent.

Transition T1D
State 1 to 5

Native rangeland has been converted for the production of forage crops or small grain products. This site often receives additional moisture from irrigation to increase production. Fertilizer and herbicides are frequently added to the Cultivated Cropland state to aid in crop production.

Restoration pathway R2A
State 2 to 1

The Altered state has lost enough soil or vegetation attributes that recovery to the Reference state will require reclamation efforts such as soil rebuilding, intensive mechanical and cultural treatments, revegetation, or all three. Examples of mechanical treatment may be brush control, while cultural treatments may include prescribed grazing, targeted brush browsing, or prescribed burning. Low-intensity prescribed fires to reduce competitive increaser plants such as needle and thread and Sandberg bluegrass. A low-intensity fire will also reduce Wyoming big sagebrush densities. Fire should be carefully planned or avoided in areas prone to annual grass infestation. The drivers for this restoration pathway are reclamation efforts along with proper grazing management.

Transition T2A
State 2 to 3

As improper grazing management continues, the vigor of bunchgrasses will decrease and the shorter grasses and shrubs will increase, leading to the Degraded state. Prolonged drought will provide a competitive advantage to shrubs, allowing them to co-dominate with grasses. The shrub canopy will increase. Key transition factors include: an increase in native shrub canopy cover; a reduction in bunchgrass production; a decrease in total plant canopy cover and production; increases in mean bare patch size; increases in soil crusting; decreases in the cover of biotic crusts; decreases in soil aggregate stability; and evidence of erosion, including water flow patterns and litter movement.

Transition T2B
State 2 to 4

Invasive species can occupy the Altered state and drive it to the Invaded state. The Altered state is at risk if invasive seeds or other viable material are present. The driver for this transition is invasive species, which make up more than 20 percent of the dry weight. The trigger is the presence of seeds or other viable material from invasive species.

Transition T2C
State 2 to 5

Native rangeland has been converted for the production of forage crops or small grain products. This site often receives additional moisture from irrigation to increase production. Fertilizer and herbicides are frequently added to the Cultivated Cropland state to aid in crop production.

Restoration pathway R3B
State 3 to 1

The Degraded state has lost enough soil or vegetation attributes that recovery to the Reference state will require reclamation efforts, such as soil rebuilding, intensive mechanical treatments, revegetation, or all three. Mulch with a high carbon to nitrogen ratio, such as wood chips or bark, in low moisture scenarios can be beneficial for slow mobilization of plant nitrogen (Whitford et al., 1989). Biochar may also be added to the system to improve soil organic carbon (SOC) which should improve cation exchange capacity (CEC), microbial activity, and hydrologic conductivity (Stavi, 2012). The drivers for the restoration pathway are the removal of increaser species, restoration of native bunchgrass species, persistent management of invasives and shrubs, and proper grazing management. Without continued control, invasive and shrub species are likely to return (probably rapidly) due to presence of seeds or other viable material in the soil and management related increases soil disturbance.

Restoration pathway R3A
State 3 to 2

Since the bunchgrass plant community has been significantly reduced, restoration to the Altered state is unlikely unless a seed source is available. If enough grass remains on the site, chemical or biological control, combined with proper grazing management, can reduce the amount of shrubs and invasive species and restore the site to the Shortgrass community. Low-intensity fire can be utilized to reduce Wyoming big sagebrush competition and allow the reestablishment of grass species. Caution must be used when considering fire as a management tool on sites with fire tolerant shrubs, such as rubber rabbitbrush, as these shrubs will sprout after a burn. Broom snakeweed and prairie sagewort may or may not re-sprout depending on conditions.

Transition T3A
State 3 to 4

Invasive species can occupy the Degraded state and drive it to the Invaded State. The Degraded state is at risk of this transition occurring if invasive seeds or viable material are present. The driver for this transition is the presence of critical population levels of invasive species. The trigger is the presence of seeds or viable material from invasive species. This state has sufficient bare ground that the transition could occur simply due to the presence or introduction of invasive seeds or viable material. This is particularly true of aggressive invasive species such as spotted knapweed and cheatgrass. This transition could be assisted by overgrazing (failure to adjust stocking rate to declining forage production), a long-term lack of fire, or an extensive drought.

Transition T3B
State 3 to 5

Native rangeland has been converted for the production of forage crops or small grain products. This site often receives additional moisture from irrigation to increase production. Fertilizer and herbicides are frequently added to the Cultivated Cropland state to aid in crop production.

Restoration pathway R4C
State 4 to 1

Restoration of the Invaded state to the Reference state requires substantial energy input. The drivers for the restoration pathway are the removal of invasive species, restoration of native bunchgrass species, persistent management of invasive species, and proper grazing management. Without continued control, invasive species are likely to return (probably rapidly) due to the presence of seeds or other viable material in the soil and management-related practices that increase soil disturbance. If invaded by conifer encroachment, treatment depends on the condition of the rangeland. Sites that have transitioned from the Degraded state to the Invaded state may be severely lacking in soil and vegetative properties that will allow for restoration to the Reference state. Hydrologic function damage may be irreversible especially with accelerated gully erosion.

Restoration pathway R4B
State 4 to 2

If invasive species are removed before remnant populations of bunchgrass are drastically reduced, the Invaded state can revert to the Altered state. The driver for the reclamation pathway is weed management without reseeding. Continued integrated pest management (IPM) will be required as many of the invasive species that can occupy the Invaded State have extended dormant seed life. The trigger is invasive species control.

Restoration pathway R4A
State 4 to 3

If invasive species are removed before remnant populations of bunchgrass are drastically reduced, the Invaded state can revert to the Degraded state. The driver for the reclamation pathway is weed management without reseeding. Continued integrated pest management (IPM) will be required as many of the invasive species that can occupy the Invaded State have extended dormant seed life. The trigger is invasive species control. Due to a lack of ground cover, the invading species cause a significant increase in soil loss (Lacey et al., 1989).

Transition T4A
State 4 to 5

Native rangeland has been converted for the production of forage crops or small grain products. This site often receives additional moisture from irrigation to increase production. Fertilizer and herbicides are frequently added to the Cultivated Cropland state to aid in crop production.