Shallow to Loamy, Calcareous 10-14 Inch Precipitation Zone Lost River Mountains
Scenario model
Current ecosystem state
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Management practices/drivers
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- Transition T1-2 More details
- Transition T1-3 More details
- Restoration pathway R2-1 More details
- Transition T2-3 More details
- Restoration pathway R3-1 More details
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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Description
The reference state consists of two dominant plant communities: The Black and Little Sagebrush (Artemisia nova & Artemisia arbuscula) dominated community and the Mixed Shrub/Bluebunch Wheatgrass community where overstory shrub canopy dominance is a mix of dwarf sagebrush species, big sagebrush species and other shrubs. The greatest difference between the two plant communities is composition and foliar cover of sagebrush (Artemisia) species. Mountain big sagebrush foliar cover increases on sites that are closer to the high end of the effective precipitation range (10 to 14 inches) and the calcium carbonate equivalency in the soil is lower, closer to minimum 15 percent concentrations outlined in the site concept.
Processes (both natural and anthropogenic) that result in state and community changes include fire, grazing, land use change, and occurrence of invasive species (Davies et al., 2011).
Characteristics and indicators
The shift between plant communities at this ecological site is generally driven by calcium carbonate concentration in soils, effective precipitation, and time since disturbance. Historically, low to mixed-severity fires occurred at relatively frequent fire return intervals of 10 to 25 years, limiting sagebrush canopy density and creating a mosaic of sagebrush stands and more open grasslands (Knick, Holmes, & Miller, 2005). Exclusion of fire (in conjunction with climate change) increases sagebrush canopy cover and can lead to more severe stand-replacing fires, oftentimes at more frequent intervals. These severe fires can drive shifts to grassland communities as well as create opportunities for invasive species establishment (Roadhouse, Irvine, & Bowerstock, 2020; Knick et al., 2005).
Improper grazing practices can also lead to an increase in sagebrush canopy cover and increased risk of severe, stand replacing fire occurrence. Removal of understory grasses can lessen the opportunities for low severity fires which leads to increased canopy densities and increases potential for severe fire disturbance events (Knick et al., 2005).
Resilience management
This site has moderate resilience as a result of the frigid soil temperature regime and xeric soil moisture regime. Resistance and resilience of a specific site have been attributed to abiotic conditions favorable to plant growth and reproduction (Maestas et al. 2016). Soils that fall within the frigid temperature regime and xeric moisture regime tend to have moderate diversity and production and are therefore more resilient, specifically in terms of resisting or recovering from invasion post-disturbance (Maestas et al., 2016).
On the LRU scale, this site may also have increased resistance to invasion of annual grasses due to the calcium carbonate concentration found in the 10 to 25-centimeter range of the soil profile. Calcareous soils have shown to provide a deterrent to the establishment of invasive grasses such as Bromus tectorum (Miller et al., 2006).
Submodel
Description
The Disturbed state consists of one community and is characterized by a nearly complete to complete loss of overstory shrub canopy. Shrub canopy loss is a result of both natural and anthropogenic disturbances, however, the most common disturbance in this LRU that results in transition to the Disturbed state from the Reference state is moderate to severe fire events. Because this LRU exists primarily on publicly managed lands (US Forest Service, Bureau of Land Management, and State), widespread anthropogenic disturbance events are infrequent. Examples of anthropogenic disturbance events include brush management through sagebrush mowing or removal treatments, chemical treatments, or improper grazing techniques that result in high-intensity hoof disturbance.
A combination of natural and anthropogenic disturbance is possible and can result in increased severity of disturbance, decreased resilience, and greater difficulty returning to the Reference State. For example, improper grazing practices that result in chronic defoliation following a fire disturbance event can increase bare ground cover, increase erosion potential, and slow the reestablishment of grass species that preclude the return of overstory sagebrush canopy (Zlatnik, 1999).
Characteristics and indicators
The primary indicator of the Disturbed state is near to complete loss of overstory sagebrush species (black sagebrush, little sagebrush, and mountain big sagebrush). A shift towards an increase in native and non-native disturbance-tolerant grasses and forbs is likely with removal of resource competition associated with sagebrush overstory. Additionally, the canopy cover of disturbance tolerant shrubs such as yellow rabbitbrush (Chrysothamnus viscidiflorus) and rubber rabbitbrush (Ericameria nauseosa) may increase. Severe disturbance events also increase the opportunity for invasion of annual grasses and weeds such as cheatgrass (Bromus tectorum) and thistle species. Percent canopy cover of invasive species is dependent on the distance of a seed source post-disturbance. Initial cover of invasive species stays below 5 percent (Zlatnik, 1999).
Resilience management
Resilience in this state is moderate. Many of the post-disturbance grasses and shrubs that are common in this state establish quickly and reach a representative canopy within 10 years post-disturbance, and continue to increase until the overstory canopy of sagebrush begins to return. However, local resilience in this state is highly dependent on current soil moisture availability, seed sources, timing and severity of the disturbance. In the instance of fire disturbance, bluebunch wheatgrass mortality can be significantly lower if the fire occurs in the spring as opposed to fall, and recovery can be impacted by the quantity of immediate post-fire precipitation (Zlatnik, 1999).
More severe disturbances increase the possibility of post-disturbance invasion. The greater the establishment of invasives, the lower the site resilience becomes, and can eventually drive a transition to the Invaded state.
Submodel
Description
When a Shallow to Loamy, Calcareous ecological site transitions to the Invaded state, it is a result of post disturbance invasion by non-native and invasive species. This state can be driven by a particularly severe disturbance either in the form of frequent or severe fire, intensive grazing that results in chronic defoliation of vegetation, land use, or repeated disturbances of low to moderate severity over short periods of time. Proximity to seed source as well as seed transport vectors play a role in likelihood of post disturbance invasion.
Characteristics and indicators
In this state, total canopy cover and production values for mid to large-sized bunchgrasses such as bluebunch wheatgrass will decrease. Traditional overstory cover and production of black sagebrush, little sagebrush, big sagebrush, and other shrubs will also decrease. These openings in the canopy will be filled with invasive annuals such as cheatgrass (Bromus techtorum) and more disturbance-tolerant forbs such as phlox species, vetch species, and Indian paintbrush (Castilleja sp.). Continued disturbance will increase cover and production of these species. Productivity and canopy cover is lower than the reference state and shifted towards the understory grass species and forbs, particularly the invasive annuals.
Resilience management
This site has low resilience primarily due to the invasive species establishment. Cheatgrass is well adapted to post disturbance establishment, particularly after wildfire disturbances. Cheatgrass takes advantage of prolific seedbanks resilient to fire and ability to rapidly establish when competition from native vegetation has been removed. Additionally, cheatgrass is able to alter fire regimes, shortening fire return intervals which provides a further advantage for cheatgrass and hinders re-establishment of native vegetation (Zouhar, 2003). Once fully established, restoration of sites invaded by cheatgrass either through natural or mechanical means has low success rates.
Submodel
Mechanism
Transition from the Reference to the Disturbed state is primarily a mechanism of severe disturbance, both natural and anthropogenic. In this this ecological site, the most likely disturbance to cause this transition is frequent or severe wildfire events. Other disturbances include but are not limited to freeze kill, insect and disease, and mechanical brush removal.
Constraints to recovery
Primary constraint to recovery is distance to seed source. When the disturbance is severe enough and the extent is great, seed source populations for sagebrush species may be removed from the vicinity. In this case, immigration and re-establishment of overstory sagebrush species can be slow. This time period can be greatly reduced through seeding and planting interventions.
Context dependence
The primary factor driving likelihood of restoration success is post disturbance weather patterns. Prolonged period of drought can slow restoration processes, whereas average to above average precipitation post disturbance can greatly increase speed and success in re-establishment of sagebrush species (Robin, 2017; Steinberg, 2002; and Fryer, 2009).
Mechanism
The transition from the reference state to the Degraded state is primarily a mechanism of severe disturbance and post disturbance establishment of invasive species. The most likely disturbance events in this LRU associated with transition to this state are severe or frequent wildfire events and repeated overgrazing that results in chronic defoliation. Following a severe disturbance, invasive and disturbance tolerant species will rapidly establish, preventing native vegetation from recovering. Other possible disturbances include but are not limited to freeze kill events, insect and disease, and mechanical brush removal.
Constraints to recovery
The most significant constraint to recovery in this state is establishment of non-native vegetation and disturbance tolerant plants. Once established, these species are able to outcompete native vegetation preventing those species from recovering to pre-disturbance levels. Effective treatment options are limited once significant populations of cheatgrass have established. Using prescribed or natural fire in conjunction with post fire seeding of native vegetation has shown success, however, reverting to cheatgrass canopy covers under five percent and returning to the reference state is highly unlikely (Zouhar, 2003).
Mechanism
The most important mechanism driving restoration from the Disturbed to the Reference State is time without sagebrush removing disturbances and distance from overstory species (sagebrush) seed source. Seeding or planting of desired overstory species in the Reference State can accelerate restoration efforts.
Context dependence
Restoration is highly dependent on time without disturbance. New sagebrush seedlings that are able to establish on a site are moderately sensitive to disturbances such as flood, freeze, and insect and disease. They are highly sensitive to herbivory and even low severity fire occurrence (Fryer, 2009 & Steinberg 2002).
Seeding and planting of desired species can speed up the restoration process, however, regeneration success with or without planting is highly dependent on localized weather patterns during this restoration period. Periods of drought will slow the process significantly, whereas periods of above normal precipitation aid in sagebrush regeneration and establishment (Innes, 2017; Steinberg 2002 & Fryer, 2009).
Mechanism
Transition from the Disturbed state to the Invaded state occurs when non-native and invasive species are able to establish in place of native vegetation following a disturbance. Invasive species such as cheatgrass are able to take advantage of the available canopy space and resources that result from removal of native vegetation following a disturbance. The speed and extent of invasive species establishment is dependent on the severity of the disturbance, distance from invasive species seed sources, and dispersal methods of invasive species.
Constraints to recovery
The most significant constraint to recovery in this state is establishment of non-native vegetation and disturbance tolerant plants. Once established, these species are able to outcompete native vegetation preventing those species from recovering to pre-disturbance levels. Often the species in this state disrupt disturbance regimes in a way that promotes further establishment . Effective treatment options are limited once significant populations of cheatgrass have established. Using prescribed or natural fire in conjunction with post fire seeding of native vegetation has shown success, however, reverting to cheatgrass canopy covers under five percent and returning to the reference state is highly unlikely (Zouhar, 2003).
Mechanism
Restoration from the Invaded state to the Reference state is resource intensive and often unsuccessful, especially when cheatgrass is the primary invasive species. Once populations of invasive species exceed five percent canopy cover, mechanical and chemical treatments are required to effectively treat a site. Seeding or planting of native species following treatments is necessary to avoid re-invasion by non-desirable species.
Context dependence
Restoration success is dependent on invasive species composition and level of establishment. Removal of cheat grass once significant establishment occurs can be resource intensive with low success rates.
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