Shallow Loamy (SwLy) Big Horn Basin Rim
Scenario model
Current ecosystem state
Select a state
Management practices/drivers
Select a transition or restoration pathway
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Transition T 1-2
Frequent and Severe Grazing and No Fire
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Transition T 1-3
Frequent and Severe Grazing (yearlong) and Wildfire or Brush Management with Drought
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Restoration pathway R 2-1
Brush Management, Prescribed Grazing, and Seeding
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Transition T 2-3
Brush Management and Frequent and Severe Grazing
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Transition T 2-4
Wildfire, Frequent or Severe Grazing, Drought with Insect Damage/Brush Management
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Restoration pathway R 3-1
Grazing Land Mechanical Treatment, Prescribed grazing and Seeding
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Transition T 3-4
Frequent and Severe Grazing, Drought, Disturbance, and Non-native seed source present
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
Select a state
Description
The Reference State (State 1) for the Shallow Loamy Ecological Site is dominated by mid-stature, cool-season bunchgrasses and rhizomatous wheatgrasses. This state persisted under grazing by large ungulates and was a resource for forage and habitat for a variety of wildlife.
Characteristics and indicators
The Reference State (State 1) is characterized by the prominent cover of bluebunch and Montana wheatgrasses (25 to 50 percent composition) and rhizomatous wheatgrasses (25 to 50 percent composition). Needle and thread and Indian ricegrass account for a significant portion of foliar cover (5 to 15 percent composition). Shrubs such as Wyoming big sagebrush and yellow rabbitbrush are primarily a minor component (5 to 20 percent composition) but will increase as the plant community moves away from the Reference State conditions.
Resilience management
The state is stable and well adapted to the Northern Intermountain Desertic Basins climate. The diversity in plant species provides resistance to influence from drought, non-native species, etc. This is a sustainable plant community (site/soil stability, watershed function, and biologic integrity).
Submodel
Description
The Mixed Shrub/Bare Ground State of the Shallow Loamy Ecological Site is dominated by shrubs as a result of extensive grazing and lack of fire. Preferred cool season grasses have been highly reduced. Remnant grasses missed by grazers such as prairie Junegrass, Sandberg bluegrass, and blue grama dominate the grass/grasslike composition. Bare ground is prominent in the interspaces between plants in this state.
Characteristics and indicators
The Mixed Shrub/Bare Ground State is characterized by the prominent cover of Wyoming big sagebrush (less than 20 percent composition). Bare ground is prevalent in the interspaces between plants. Prairie Junegrass, Sandberg Bluegrass, and blue grama continue to occur (10 to 40 percent composition).
Resilience management
The state is resistant to change and may become more fire resistant as fine fuels are reduced by continued frequent and severe grazing. Plant diversity is is moderate to poor making it more susceptible to the effects of drought or disease. Soil erosion is accelerated with the increase in bare ground and frequently result in water flow patterns on the surface.
Submodel
Description
The Sod-Former State of the Shallow Loamy Ecological Site is dominated by sod-forming grasses and grasslikes. This state occurs as a result of frequent and severe grazing and removal of brush either naturally (drought, fire) or human brush control methods. preferred cool-season grasses and shrubs are greatly reduced or lacking completely.
Characteristics and indicators
The Sod-Former State of the Shallow Loamy Ecological Site is characterized by the prominent cover of blue grama and threadleaf sedge in large patches (25 to 70 percent cover). Overall production is greatly reduced compared the Reference State and Mixed Shrub/Bare Ground State.
Resilience management
The Sod-Former state is extremely resistant to change and the plant diversity is extremely low. Water infiltration is greatly reduced which protects that site itself but can result in increased runoff around the edges of the mat.
Submodel
Description
Wyoming rangelands, much like the neighboring states, has quickly fallen victim to the aggressive invasion of cheatgrass, also called downy brome (Bromus tectorum). The rapid development of an extensive seedbank and duff layer forms with the potential for multiple growth cycles throughout a year. The advantageous ability of cheatgrass to persist through the winter under a blanket of snow and sprout early makes it difficult for natives to outcompete it for limited resources. Shifts in climatic patterns, changes in management, and exposure to human activity are a few of the explanations for the current flush and rapid expansion across the western United States. Although cheatgrass is the most prevalent large-scale threat for rangeland managers, a variety of knapweeds (spotted, Russian, etc.), in combination with other aggressive invaders such as whitetop (hoary cress), black henbane, field bindweed, and leafy spurge are increasing in density and frequency, producing their own set of challenging management issues. As more species are found or as other species become more prevalent on a large scale, the community dynamics in this state will shift in response to the concerns of the identified species.
Characteristics and indicators
The Invaded State (State 4) is characterized by the presence and eventual dominance of invasive and non-native species. The open canopy of the arid native community combined with extended periods of drought alone or in combination with overutilization, insect damage, or wildfire, has weakened the native composition, thus allowing invasion.
Resilience management
The competitive nature of annuals and other invasive species creates a complex environment that inhibits control and makes it implausible to attain complete eradication once an invasive species has established on the landscape.
Submodel
Mechanism
Frequent and severe grazing plus no fire will convert the plant community to the Mixed Shrub/Bare Ground Plant Community. The probability of this occurring is high, especially evident on areas with historically higher precipitation and where drought or heavy browsing does not adversely impact the sagebrush stand.
Mechanism
Frequent and severe grazing (yearlong grazing) plus wildfire or brush control, will convert
the plant community to the Sod-Former State. The probability of this occurring is high, especially if the sagebrush stand has been severely affected by drought or
heavy use or has been removed altogether.
Constraints to recovery
The ability to weaken or break up the sod-forming species and the lack of remaining native (key) bunchgrasses are the main constraints to recovery for this community.
Context dependence
The time lapse for the occurrence of this state is varied. It is a transition that takes or may take a significant time frame (over ten years) to occur. Recovery may be able to be achieved; but at this time no proof of recovery, without mechanical interference, has been achieved/documented within a management time frame (25 years).
Mechanism
Brush management, followed by prescribed grazing, will return this plant community at or near the Reference State (State 1). Reseeding after brush management with native species may be necessary to ensure a more rapid transition. If prescribed fire is used as a means to reduce or remove the shrubs, sufficient fine fuels will need to be present. This may require deferment from grazing prior to treatment. Post management is critical to ensure success. This can range from two or more years of rest to partial growing season deferment, depending on the condition of the understory at the time of treatment and the growing conditions following treatment. In the case of an intense wildfire that occurs when desirable plants are not completely dormant, the length of time required to reach the Reference State (State 1) may be increased and seeding of natives is recommended.
Mechanism
Brush management, or an intense wildfire followed by frequent and severe grazing, will convert the plant community to the Sod-Former State.
Mechanism
Fire (wild), Frequent or Severe Grazing, Drought with Insect Damage/Brush Management – Throughout most of this LRU there is a seed source present for cheatgrass, knapweed, and other invasive species. Stress to the native community from fire, drought, disease/insect damage to sagebrush, or ground/soil disturbance including impacts by grazing large herbivores or recreational uses; opens the canopy and exposes the soil, creating a niche for undesirable and invasive species to establish. Early detection and rapid response provides a chance to prevent a full-scale invasion, but if left untreated, infestations can establish rapidly and spread with one growing season. The population soon grows exponentially as further stress or disturbance occurs. In some cases, once the invasive species are established, they can create their own habitat; this reduces the competitive ability of native species. The open canopy of the Mixed Shrub/Bare Ground State is vulnerable to invasive species without further influence. With continued over-use, drought, or insect damage/disease, the invasive species will establish and quickly dominate a location. The threshold species in this system is Wyoming big sagebrush, which protects the remnants of the perennial native grasses, allowing them to persist on the landscape.
Constraints to recovery
The lack of sufficient key native species and the inability to eradicate or sufficiently control invasive species are the main constraints to recovery for this state.
Context dependence
Extent of the transition for the Mixed Shrub/Bare Ground State to the Invaded State will determine the severity of the recovery constraints. The loss of shrubs from this state will further limit/remove any ability of this state to recover back to any previous state.
Mechanism
Grazing land mechanical treatment (chiseling, etc.) and plains prickly pear cactus control (if needed), followed by prescribed grazing, will return this plant community to near Reference State (State 1) condition. Reseeding with natives is often needed to hasten this transition.
Mechanism
Frequent and severe grazing, drought, or disturbance with a seed source present—Increased interspatial gaps in these communities leaves exposed soil that is vulnerable to invasion by undesirable species. Increased pressure from overuse and drought work to weaken the sod or mat-like community, exposing soil further to annuals and other invaders, such as cheatgrass and knapweeds. The aggressive nature and altered hydrology of these sites do restrict weed invasion. But if a seed source is available, ground disturbance by herbivores or man-induced, allows invasive species to find a way into the community. Once established in the community, it may not be feasible to completely remove eradicate the invasive species. Once the invasive species have become prevalent on the landscape (less than 5 percent composition), the community crosses the threshold into the Invaded State.
Constraints to recovery
The lack of ability to eradicate or remove invasive species from the community at this time is the constraint to any recover from the invader driven state.
Context dependence
Substantial evidence that a blue grama dominated community has shifted to a invaded community has not been gathered. It has been documented where a significant population of invasive species (ex: cheatgrass) has established within the interspaces of the blue grama sod.
Model keys
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