Shallow To Gravel (SwGr) Big Horn Basin Rim
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
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Transition T1-2
Frequent or high-intensity herbivory weakens the ability of the grasses to persist, especially during prolonged drought. Removal of or significant decrease in key grasses and a shift to a more pronounced sagebrush community renders a site difficult to restore back to the Reference State without mechanical or similar treatments.
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Transition T1-3
Long duration, high-intensity grazing reduces the bunchgrass component and encourages the mat- or sod-forming species. Prolonged drought stresses plants, opening the canopy for sod-formers. Removal of sagebrush by disturbances opens the canopy, aiding the transition.
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Restoration pathway R2-1
Removal or thinning of the sagebrush by mechanical or chemical means or by fire with remnant populations of native perennial desired grass species will lead to this community, if time is given for recovery and seedling establishment. Frequent use of this community during the dormant season will work to reduce the sagebrush through trampling and grazing but may encourage shorter-statured, more tolerant species and not the more desired species.
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Transition T2-3
Sod-forming species such as blue grama can tolerate high levels of use and will maintain as other native species decline. This decline creates a sagebrush–sod-former community that is resistant to change with management. Impacts to sagebrush by disease or insect damage will shift this to the secondary community phase.
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Transition T2-4
When seed sources are prevalent for invasive species, stress from drought, wildfire, or other natural and man disturbances, removes or exposes the soil and presents a niche for invasion by undesirable weeds.
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Transition T3-4
The interstitial spaces within the patchy canopy of sod-formers leaves areas for weedy species to establish, especially with disturbance or high traffic areas.
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Restoration pathway R4-5
Integrated pest management plan and intense weed control after and possibly before seedbed preparation will be necessary to overcome a severe weed infestation.
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Transition T5-4
After a land disturbance occurs or with reclamation processes, if no management is put into place to prevent further disturbance, or to encourage seeding establishment and prevent an infestation of weeds, the community will revert or transition to an invaded state.
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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State 1
Bunchgrass/Sagebrush
Description
The Reference State, State 1, is labeled as the Bunchgrass/Sagebrush State. Wyoming big sagebrush and mid-stature bunchgrasses are the dominant contributors to composition with a notable cover of perennial forbs. Cover in this Reference State is reduced (increased bare ground) from similar ecological sites (Loamy and Sandy), due to the gravel substratum that reduces the available moisture in the lower soil profile.
Characteristics and indicators
This State is characterized by ten percent or less composition by cover of Wyoming big sagebrush, with a dominant understory of bluebunch wheatgrass, needle and thread, and Indian ricegrass (30-50 percent composition). Areas of western wheatgrass exist with the other minor components including prairie Junegrass, bottlebrush squirreltail, Sandberg bluegrass, threadleaf sedge, and blue grama.
Resilience management
The plant community is diverse and is adapted to the arid and unpredictable nature of the environment creating a resilient community. In extended periods of drought, species such as needle and thread and western wheatgrass are able to limit production until conditions are suitable. Once conditions have improved they are prolific producers. Sandberg bluegrass is another species that can respond quickly to the drastically changing precipitation and climate patterns of the Big Horn Basin.
Historically, the Reference State evolved under a low fire frequency, estimated to be 195 to 235 years between burns on the same community patch, and sagebrush has a post-fire recovery time of 50-120 years or more in arid systems (Baker, 2006) and with grazing pressure by large ungulates (elk, bison, deer, or antelope).
Submodel
Description
Frequent and severe use by livestock or wildlife leads to a decline of the herbaceous species, creating the Mixed Shrub/Bare Ground State. This State can be exacerbated by extended periods of drought, insects and other natural and human disturbances. The percentage of composition by cover and production is swayed by the decrease of herbaceous vegetation and the relative stability of woody production, creating the appearance of increased canopy by shrubs.
Characteristics and indicators
The gravelly and coarse textured lower soil profile provides the opportunistic shrubs such as yellow and rubber rabbitbrush, and fringed sagewort to establish along with Wyoming big sagebrush. These shrubs provide a protective niche for most herbaceous understory to maintain a minimal cover in difficult conditions. The additional moisture provided by the shade of the canopy as well as protection from grazing benefit most native grasses.
Resilience management
As the grass cover declines and the plant community continues to weaken, the sagebrush and other shrub cover is susceptible to attack by insects, disease, and age. The loss of the woody cover from the system places this State at-risk of invasion or transition to a more degraded state.
The lack of water retention lower in the soil profile exacerbates the impact of drought and limits the resiliency of the Shallow to Gravel Ecological site. Animal trailing, foot and vehicle trails and other erosional patterns are highly visible in this State. Loss of top soil exposing the gravel layers is a potential with the increased wind and water erosion risks within this State.
Risk of wildfire within this state is marginal due to the lack of fine fuels within the understory; however, the canopy of the woody vegetation will carry a fire under certain weather conditions. Fire is a significant risk to this community because of the potential to remove all native vegetation. The exposed community is vulnerable to erosion and invasion by cheatgrass with no native competition and a lack of native seed source to allow recovery. Loss of sagebrush reduces the hydrology further hindering the recovery potential.
Submodel
Description
The dominant sod-forming grasses that currently exists within this LRU and subset is blue grama and threadleaf sedge. Both blue grama and threadleaf sedge are native components in Reference communities within this ecological site. The trend is for these species to increase, becoming the dominant cover, with prolonged drought, shifts in climate, or under grazing pressure.
Characteristics and indicators
This community is characterized by a dominance of blue grama with interspersed patches of threadleaf sedge.. Remnants of the other key vegetation will persist, but is limited by the dense mats created by the sod-formers. The remnants are restricted to the protective niche within sagebrush canopy or cactus clumps.
Resilience management
Blue grama and threadleaf sedge effectively alters the hydrology of the site by increasing the surface runoff from the dense shallow root system that inhibits the movement of water through the soil surface. This root mat directs surface flow around the edge of the mat concentrating flow into channel-like patterns and off-site. This loss of surface moisture creates a drier environment for native grass species and forbs to persist.
Submodel
State 4
Invaded
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 is characterized by the presence and eventual dominance of invasive and non-native species. The open canopy of the arid native community combined with extended periods of drought, extensive grazing impacts, insect damage, other natural disturbance or any combination there of, has weakened the native composition allowing invasion.
Resilience management
The competitive nature of annuals and other invasive species creates a hostile environment that restrict the native species, inhibits control and makes it implausible to attain complete eradication once an invasive species has established on the landscape. Severity and scale of invasion will make a difference in the limitations of the site.
Submodel
Description
The arid nature of this region has played a major role in the development and transitions in land use over time. Early settlers worked to farm any land that was accessible by water (canal systems) and equipment. Many of these small areas were later abandoned and left to return to rangeland. Other landscapes were treated with a variety of prescriptions to manage or eradicate sagebrush. Tillage of the soil, changes in hydrology caused by the loss of vegetative structure, constant natural climatic fluctuations, and advancements in seed sources has led to the creation of a site description for the Altered State.
The Altered state could be drafted as a alternative land use within the State-and-Transition Model diagram. No matter how a location is classified, once the site has experienced an event that has altered the soil properties (erosional, depositional, hydrological, or chemical), the site potential is altered. The Shallow to Gravel ecological site, once mined or tilled, potentially will lose the top soil or gain chemistry that could potentially change the ecological site the soil would key to. In some cases (site by site consideration), recorrelation of a location may be needed. In many cases, however, the soils have not been altered out of the current site characteristics, but the potential has shifted enough that it is no longer truly comparable to the Reference State (State 1).
Characteristics and indicators
Mechanical, cultural, or natural disturbance to soils resulting in an alteration of structure, hydrologic function, and possibly stability prevent a site from supporting the native vegetation or responding to management in the same way as an undisturbed site. Reclamation or restoration of an area will not replace the original function and factors that made the original location respond as it did. Therefore, these "altered" lands may, after significant inputs and time, resemble the Reference Communities (1.1 or 1.2), but they will not respond or function as the Reference Community.
Resilience management
The species selection, extent or occurrence of tillage, and the resulting loss of structure, moisture, biotic degradation, changes in infiltration and water-holding capacity, and change in permeability are all factors that affect a planted site. The time required and feasibility for the redevelopment of soil, as well as variability in plant establishment and climatic conditions determine the successional path after a disturbance event. Kochia, Russian thistle, and mustards are the typical primary successional species in this LRU. Although they provide organic material, nutrient flow and erosional protection, they lack the structure and root system to fully stabilize the site. With time, the site may become similar in composition to Reference, but the integrity of the soil is altered, changing community potential. To capture the dynamics of this process, an Altered State was added to document these communities.
Submodel
Mechanism
Frequent and severe grazing (year-long) or drought with the absence of brush management or wildfire—The conversion to a Wyoming Big Sagebrush/Bare Ground plant community is a response to extended periods of stress, both climate- and human-induced. Frequent or high-intensity herbivory with minimal to no recovery period weakens the ability for the grasses to persist, especially during prolonged drought. With the weakened herbaceous cover, the composition will shift to predominantly Wyoming big sagebrush. Over time sagebrush composition will increase inhibiting the recovery. With added climatic stress, species diversity and productivity are lost, and the community crosses into the Sagebrush/Bare Ground State. An illusion of crossing the threshold to State 2 is created in extended periods of significant fluctuation in precipitation patterns affecting production of prominent plants within this system. The loss of species diversity and increased bare ground over a period of years, along with lack of litter are the indicators that a true transition has occurred. It is important to recognize that woody cover is a factor of the number of plants as well as canopy cover. In some instances, the number of actual sagebrush plants may not increase to cause this shift, but the change in composition or vigor of the wood canopy, as well as the loss of herbaceous canopy, creates the perception of an increased number of plants when it is the ratio, size, and age that is more likely to shift.
Constraints to recovery
Having sufficient key species and cooperation of precipitation and rest from use to allow the native bunchgrasses to re-establish within the interspaces of sagebrush is the main constraint to recovery. Being able to thin while maintaining some woody cover may also be challenging for the recovery process.
Mechanism
Frequent grazing (year-long), brush management, or fire with drought—Severe and frequent grazing reduces vigor and presence of key species, mainly needle and thread and Indian ricegrass, and short-statured grasses become dominant. Animal disturbance (hoof impact) and continuous use reduces the bunchgrass component by allowing repeated defoliation of the desirable species and damage to the structure of the plant. These impacts reduce recovery potential and ground cover for insulation and snow catch; weakening and, over time, removing select species. The open canopy and hoof impact encourage species that are tolerant to trampling and short bursts of spring and summer precipitation. These species generally are tillering, mat- or sod-forming species such as blue grama and threadleaf sedge. Prolonged drought stresses the plants and opens the canopy, allowing sod-formers to fill in the interspaces. The shallow, dense root mats will continue to spread over time. The added removal of sagebrush with animal impacts or with fire or brush management may open the canopy more and aid in establishment. Season of use and intensity of grazing (time and timing) are triggers that can reduce the risk of transitioning, or, if done improperly, can force the transition to occur rapidly. The increase in blue grama adds an element of midsummer growth that extends the “green” grazing window. However, adequate amounts and timing of moisture must occur to allow sufficient growth to prevent overuse of the cool-season species.
Constraints to recovery
The ability to weaken or break up the sod-forming species and the lack of remaining native (key) bunchgrasses are the main constraints to recovery for this community.
Context dependence
The time lapse for the occurrence of this state is varied. It is a transition that takes or may take a significant time frame (over ten years) to occur. Recovery may be able to be achieved; but at this time no proof of recovery, without mechanical interference, has been achieved/documented within a management time frame (25 years).
Mechanism
Prescribed grazing with brush management or wildfire—Thinning or patch treatments for sagebrush allow native herbaceous cover to respond to improved moisture and sunlight followed by prescribed grazing to prevent will help this community recover. Treatment will vary depending upon the existing composition of grasses remaining and the potential threats to the location. Removal or thinning of the sagebrush within this community will help to reduce competition, encouraging grasses and forb recovery if the disturbance or overuse (recreational or grazing pressure) is reduced. Drought may prolong the time required for recovery. Mowing or mulching sagebrush trials have shown a strong response by grasses with little to no recovery time post-treatment. The resulting community with these treatments is driven by the dominant species within the community pre-treatment or climatic and treatment conditions during and following may sway the community. It is crucial to investigate the immediate and surrounding area around treatment sites to ensure no invasive species (cheatgrass) are present before treatment type is decided and then applied. The arid climate and lack of fine fuels limits the feasibility of fire as a brush management tool in this system.
Mechanism
Drought, Disease or Insect Damage, Over-use, or Fire - Sod-forming species such as blue grama and threadleaf sedge can tolerate high levels of use and will maintain as other native species decline. Hoof action or compaction inhibits more desirable native species, allowing the sod-formers to become dominant on the landscape. This decline creates a sagebrush/sod community that is resistant to change with management. Impacts to sagebrush by disease or insect damage, as well as drought or herbivory, will shift this to the secondary community phase with cactus as a subdominant cover with blue grama.
Constraints to recovery
The hydrologic shift caused by blue grama and the tolerance and resiliency of this species limits the ability to weaken/reduce its foothold in the community enough to encourage the mid-stature bunchgrasses key to this site.
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 Sagebrush/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 sagebrush/bare ground state to the invaded state will determine the severity of the recovery constraints. The loss of sagebrush from this state will further limit/remove any ability of this state to recover back to any previous state.
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/Sagebrush State (State 4).
Constraints to recovery
The lack of ability to eradicate or remove invasive species from the community at this time is the constraint to any recover from the invader driven state.
Context dependence
Substantial evidence that a blue grama dominated community has shifted to a invade/sagebrush or invaded community has not been gathered. It has been documented where a significant population of invasive species (ex: cheatgrass) has established within the inter-spaces of the blue grama sod.
Mechanism
Integrated pest management with seeding—Integrated pest management with intense weed control pre- and post-seeding is necessary to overcome a severe weed infestation. Thorough seedbed preparation and use of improved varieties (native and introduced species) suited for the intended land use improves the success potential. Seed mixes are generally designed to be similar to the Reference Community Phase (1.1). The limited success of seedings, lack of seed sources for all native species, the mechanical preparation of the seedbed alters soil stability and hydrologic functions, which in turn inhibits the restoration for this site. The alteration of the soils, the change in the plant community, and the risk of reinvasion of the site inhibits its ability to react the same to management and environmental changes as a non-disturbed native community will. Once significant soil disturbance occurs, the community will remain in an Altered State.
Context dependence
Species of concern (invasion) will be the determining factor to what processes will need to occur to allow an invaded community to be restored/reclaimed.
Relevant conservation practices
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Critical Area Planting |
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Prescribed Grazing |
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Grazing Land Mechanical Treatment |
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Range Planting |
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Heavy Use Area Protection |
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Upland Wildlife Habitat Management |
Mechanism
No use, fire (wild or prescribed), frequent or severe grazing, drought with seed source present—Lack of management to prevent further disturbance or lack of use following reclamation allows the community to revert or transition to an invaded state. Wildfire, prescribed burning, drought, or frequent and severe use by large herbivores can be disturbances that either opens the canopy or introduces the species to the location. Extended periods of non-use create a decadent community with a large proportion of dead growth persisting around the crown of the plants, reducing vigor and production. Loss of vigor and increased bare ground makes the community vulnerable to weed invasions. Frequent or severe grazing, drought, or fire will also open the canopy and assist with the incorporation of seed sources encouraging an invasion and transition to the Invaded State.
Constraints to recovery
The species of invasion is the major constraint to recovery. Eradication has been unsuccessful for most of the major species affecting these communities on a large scale.
Model keys
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The Ecosystem Dynamics Interpretive Tool is an information system framework developed by the USDA-ARS Jornada Experimental Range, USDA Natural Resources Conservation Service, and New Mexico State University.