State 1
Reference State

The Reference State is a representative of the natural range of variability under pre Euro settlement conditions. The Reference State has three general community phases; a shrub-grass dominant phase, a perennial grass dominant phase and a shrub dominant phase. State dynamics are maintained by interactions between climatic patterns and disturbance regimes. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These include the presence of all structural and functional groups, low fine fuel loads, and retention of organic matter and nutrients. Plant community phase changes are primarily driven by fire, periodic drought and/or insect or disease attack.

Community 1.1
Reference Plant Community

The representative community phase is characterized by a dense stand of tall, cool-season perennial grasses with scattered basin big sagebrush. The plant community is dominated by bluebunch wheatgrass. Other important perennial grasses include basin wildrye and streambank wheatgrass. Potential vegetative composition is approximately 80% grasses, 15% shrubs and 5% forbs. Approximate ground cover (basal and crown) is 55 to 65 percent. Bare ground is approximately 20 percent.

Community 1.2
Community phase

This community phase is characteristic of a post-disturbance, early-seral community. Basin wildrye, Nevada bluegrass and other perennial grasses and grass-likes dominate. Rabbitbrush is present in minor amounts. Depending on fire severity or intensity of Aroga moth infestations, patches of intact sagebrush may remain.

Resilience management. Burning bluebunch wheatgrass may remove most of the aboveground biomass but does not usually result in plant mortality. Bluebunch wheatgrass is generally favored by burning and increases post-fire. Basin wildrye is relatively resistant to fire as plants sprout from surviving root crowns and rhizomes (Zschaechner 1985). Miller et al. (2013) reported increased shoot densities in the first year following the wildfire with a return to normal shoot production by year two.

Community 1.3

Sagebrush increases in the absence of disturbance. Decadent sagebrush dominates the overstory and the deep-rooted perennial bunchgrasses in the understory are reduced either from competition with shrubs and/or from herbivory.

Community 1.4

Pathway 1.1a
Community 1.1 to 1.2

Fire significantly reduces cover of shrubs and mature bunchgrasses and leads to a early/mid-seral community, dominated by grasses and forbs.

Pathway 1.1b
Community 1.1 to 1.3

Time and lack of disturbance such as fire allows for sagebrush to increase and become decadent. Long term drought, herbivory, or combinations of these will cause a decline in perennial bunchgrasses and fine fuels leading to a reduced fire frequency and allowing big sagebrush to dominate the site.

Pathway 1.2a
Community 1.2 to 1.1

Time and lack of disturbance will allow sagebrush to increase. Regeneration of sagebrush depends on near by seed source and favorable soil moisture conditions. Completion of this community phase pathway may take a decade or longer.

Context dependence. Basin big sagebrush returns to a site primarily from seeds of plants that survived in unburned patches. Approximately 90% of big sagebrush seed is dispersed within 30 feet (9 m) of the parent shrub (Goodrich et al. 1985) with maximum seed dispersal at approximately 108 feet (33 m) from the parent shrub (Shumar and Anderson 1986). Regeneration of basin big sagebrush after stand replacing fires is therefore both difficult and dependent upon proximity of residual mature plants and favorable moisture conditions (Johnson and Payne 1968, Humphrey 1984).

Pathway 1.3a
Community 1.3 to 1.2

Fire will decrease or eliminate the overstory of sagebrush and allow for the perennial bunchgrasses to dominate the site. Fire will typically remove most of the sagebrush overstory. A severe infestation of Aroga moth could also cause a large decrease in sagebrush within the community, giving a competitive advantage to the perennial grasses and forbs.

State 2
Current Potential

This state is similar to the Reference State 1.0. Ecological function has not changed, however the resiliency of the state has been reduced by the presence of invasive weeds. Non-natives may increase in abundance but will not become dominant within this State. These non-natives can be highly flammable and can promote fire where historically fire had been infrequent. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These feedbacks include the presence of all structural and functional groups, low fine fuel loads, and retention of organic matter and nutrients. Positive feedbacks decrease ecosystem resilience and stability of the state. These include the non-natives’ high seed output, persistent seed bank, rapid growth rate, ability to cross pollinate, and adaptations for seed dispersal.

Community 2.1
Community Phase

This community phase is similar to the Reference State Community Phase 1.1, with the presence of non-native species in trace amounts. Bluebunch wheatgrass and basin wildrye dominate the site. Forbs and native shrubs and other perennial grasses/grasslikes make up smaller components of this site. Non-natives are present, but do not dominate.

Community 2.2
Community Phase

This community phase is characteristic of a post-disturbance, early/mid seral community where annual non-native species are present. Perennial bunchgrasses and grass-likes dominate the site and patches of intact sagebrush may remain. Rabbitbrush may be sprouting. Non-native species are stable or increasing within the community.

Resilience management. Depending on fire severity, rabbitbrush may increase after fire. Rubber rabbitbrush is top-killed by fire, but can rebound after fire (Young 1983). Shortened fire intervals within this ecological site favor a creeping wildrye understory with a rabbitbrush dominate overstory.

Community 2.3
Community Phase

This community is at risk of crossing a threshold to another state. Sagebrush dominates the overstory and the perennial bunchgrasses understory is reduced, either from competition with shrubs, inappropriate grazing, lowered water table or a combination of the three. Rabbitbrush may be a significant component. Beardless wildrye or Sandberg bluegrass may increase and become co-dominant with deep-rooted bunchgrasses. Non-native species are stable or increasing due to lack of competition with perennial bunchgrasses. This site is susceptible to further degradation from inappropriate grazing, drought, and repeated wildfire.

Pathway 2.1a
Community 2.1 to 2.2

Fire will decrease or eliminate the sparse stand of sagebrush and perennial bunchgrasses and grass-likes remain dominant on the site. Fire will typically remove most of the sagebrush overstory and rabbitbrush will likely resprout. A severe infestation of Aroga moth could also reduce sagebrush giving a competitive advantage to perennial grasses and forbs. Non-native species are likely to increase after fire.

Context dependence. The effect of fire on bunchgrasses relates to culm density, culm-leaf morphology, and the size of the plant. The initial condition of bunchgrasses within the site, in addition to seasonality and intensity of the fire factor into the individual species’ responses. For most forbs and grasses, the growing points are located at or below the soil surface, providing relative protection from disturbances that decrease above-ground biomass, such as grazing or fire. Thus, fire mortality is more correlated to the duration and intensity of the wildfire (Wright 1971, Young 1983). Depending on fire severity, rabbitbrush may increase after fire. Rubber rabbitbrush is top-killed by fire, but can rebound after fire (Young 1983). Shortened fire intervals within this ecological site favor a creeping wildrye understory with a rabbitbrush dominate overstory.

Pathway 2.1b
Community 2.1 to 2.3

Time and lack of disturbance such as fire allows for sagebrush and rabbitbrush to increase and become decadent. Long term drought, herbivory, or combinations of these will cause a decline in perennial bunchgrasses and fine fuels leading to a reduced fire frequency and allowing big sagebrush and rabbitbrush to dominate the site. Inappropriate grazing management reduces the perennial bunchgrass understory; conversely beardless wildrye and/or bluegrass increase in the understory depending on grazing management.

Pathway 2.2a
Community 2.2 to 2.1

Time and lack of disturbance and/or grazing management that favors the establishment and growth of sagebrush and rabbitbrush allows the shrub component to recover. The establishment of big sagebrush can take many years.

Context dependence. Basin big sagebrush returns to a site primarily from seeds of plants that survived in unburned patches. Approximately 90% of big sagebrush seed is dispersed within 30 feet (9 m) of the parent shrub (Goodrich et al. 1985) with maximum seed dispersal at approximately 108 feet (33 m) from the parent shrub (Shumar and Anderson 1986). Regeneration of basin big sagebrush after stand replacing fires is therefore both difficult and dependent upon proximity of residual mature plants and favorable moisture conditions (Johnson and Payne 1968, Humphrey 1984).

Pathway 2.3a
Community 2.3 to 2.2

Fire will decrease or eliminate the overstory of sagebrush and allow for the perennial bunchgrasses to dominate the site. Fire will typically remove most of the sagebrush overstory. A severe infestation of Aroga moth could also cause a large decrease in sagebrush within the community, giving a competitive advantage to the perennial grasses and forbs. Non-native species respond well to fire and may increase post-burn.

Context dependence. The effect of fire on bunchgrasses relates to culm density, culm-leaf morphology, and the size of the plant. The initial condition of bunchgrasses within the site, in addition to seasonality and intensity of the fire factor into the individual species’ responses. For most forbs and grasses, the growing points are located at or below the soil surface, providing relative protection from disturbances that decrease above-ground biomass, such as grazing or fire. Thus, fire mortality is more correlated to the duration and intensity of the wildfire (Wright 1971, Young 1983).

State 3
Shrub Dominated

This state typically results from many years of heavy grazing during time periods harmful to perennial bunchgrasses and/or hydrologic modification resulting in a lowered water table. Creeping wildrye and/or Sandberg bluegrass increase and may become the dominant grass. Sagebrush dominates the overstory and rabbitbrush may be a significant component. Sagebrush may be decadent, reflecting stand maturity. The shrub overstory and creeping wildrye or bluegrass understory dominate site resources such that soil water, nutrient capture, nutrient cycling and soil organic matter are temporally and spatially redistributed.

Community 3.1
Community Phase

Decadent sagebrush dominates the overstory. Rabbitbrush may be a significant component. Deep-rooted perennial bunchgrasses such as bluebunch wheatgrass and basin wildrye may be present in trace amounts, but are not common. Beardless wildrye and Sandberg bluegrass and annual non-native species increase. Bare ground may increase.

Community 3.2
Community Phase

Bluebunch wheatgrass and basin wildrye are absent or minor in this community phase. Creeping wildrye and/or Sandberg bluegrass and rabbitbrush dominate the site; annual non-native species may be present but are not dominant. Trace amounts of sagebrush may be present.

Resilience management. Depending on fire severity, rabbitbrush may increase after fire. Rubber rabbitbrush is top-killed by fire, but can rebound after fire (Young 1983). Shortened fire intervals within this ecological site favor a creeping wildrye understory with a rabbitbrush dominate overstory. Rabbitbrush has a large taproot and is known to be shorter-lived and less competitive than sagebrush. Seedling density, flower production, and shoot growth decline as competition from other species increases (McKell and Chilcote 1957, Miller et al. 2013, Young and Evans 1974).

Pathway 3.1a
Community 3.1 to 3.2

Fire or heavy fall grazing that causes mechanical damage to shrubs, and/or brush treatments with minimal soil disturbance, will greatly reduce the overstory shrubs to trace amounts and allow for creeping wildrye, mat muhly, or Sandberg bluegrass to dominate the site.

Pathway 3.2a
Community 3.2 to 3.1

Absence of disturbance and natural regeneration overtime allows sagebrush to recover.

Context dependence. Basin big sagebrush returns to a site primarily from seeds of plants that survived in unburned patches. Approximately 90% of big sagebrush seed is dispersed within 30 feet (9 m) of the parent shrub (Goodrich et al. 1985) with maximum seed dispersal at approximately 108 feet (33 m) from the parent shrub (Shumar and Anderson 1986). Regeneration of basin big sagebrush after stand replacing fires is therefore both difficult and dependent upon proximity of residual mature plants and favorable moisture conditions (Johnson and Payne 1968, Humphrey 1984).

State 4
Eroded State

This state is characterized by the loss of deep-rooted native perennials, dominance of non-native species and active soil erosion. Dominance of non-native annuals are most common, but dominance of perennial non-native species, like whitetop (Lepidium latifolium) may also occur. Bare ground exceeds site concepts and soil, nutrients and precipitation are redistributed off site. Excessive soil erosion may result in gully development and a significant reduction of soil moisture.

Community 4.1
Community Phase

Non-native species dominate the plant community. Bare ground and soil loss is significant. Annual non-native species are common and may dominate. Introduced species such as forage kochia (Bassia prostrata) or crested wheatgrass are present, depending on previous restoration attempts. Trace amounts of big sagebrush may be present, especially if seeded. Infiltration has been reduced and run-off has become more rapid.

Transition T1
State 1 to 2

Trigger: introduction of non-native annual and perennial plants, such as cheatgrass, mustards, and whitetop. Slow variables: Over time the non-native species will increase within the community. Organic matter inputs are reduced. Threshold: Any amount of introduced non-native species causes an immediate decrease in the resilience of the site. Non-native species cannot be easily removed from the system and have the potential to significantly alter disturbance regimes from their historic range of variation.

Transition T2
State 2 to 3

Trigger: Hydrologic altering of the site (i.e. gulling of associated channel upstream followed by severe soil erosion). Maybe also be coupled with repeated, inappropriate, growing season grazing and prolonged drought. Slow variables: Long term decrease in deep-rooted perennial grass density and increased Sandberg bluegrass favors shrub growth and establishment resulting in reduced organic matter inputs and soil stabilization. Threshold: Loss of deep-rooted perennial bunchgrasses changes nutrient cycling, nutrient redistribution, and organic matter inputs. Alteration in the hydrology of the site caused by soil erosion and gullying reduces soil moisture by increasing runoff and reducing infiltration.

Transition T3
State 2 to 4

Trigger: Wide spread and repeated wildfire or soil disturbing practices (failed seeding or abandon farmland) coupled with prolonged drought. Slow variables: Increased production and cover of non-native species over time. Threshold: Loss of deep-rooted perennial bunchgrasses and shrubs truncates, spatially and temporally, nutrient, energy, and moisture capture/cycling within the community.

Restoration pathway R1
State 3 to 2

Brush management such as mowing, coupled with seeding of bluebunch wheatgrass and other native perennials. This may be coupled with restoration of the water table where channel incision has occurred. Engineered structures may be needed. See USDA, NRCS National Engineering Handbook (2008). This restoration pathway should include prescribed grazing management and minimize soil disturbing practices. A failed restoration attempt may transition the site to an annual dominated state (State 4).

Transition T4
State 3 to 4

Trigger: Severe and repeated wildlife and/or failed brush management and seeding, maybe be coupled with prolonged drought. Slow variables: Increased production and cover of non-native annual species over time. Threshold: Loss of deep-rooted perennial bunchgrasses and shrubs truncates, spatially and temporally, nutrient capture and cycling within the community.

Restoration pathway R2
State 4 to 2

Restoration efforts should include seeding of bluebunch wheatgrass and other native species coupled with prescribed grazing management. The site may also require restoration of the water table where channel incision has occurred. Engineered structures may be needed. See USDA, NRCS National Engineering Handbook (2008). Probability of success is dependent on adequate soil moisture conditions and care should be taken to minimize soil disturbing practices.