Steep Loamy 15-19 Inch Precipitation Zone Lost River Mountains
Scenario model
Current ecosystem state
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Management practices/drivers
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- Transition T1A More details
- Transition T1B More details
- Restoration pathway R2A More details
- Transition T2A More details
- Restoration pathway R3A 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 of the Steep Loamy 15 to 19 inch ecological site consists of three dominant plant communities. Community 1.1 and 1.2 are dominated by a mountain big sagebrush (Artemisia tridentata ssp. vaseyana) overstory; however, Community 1.1 has a dominant understory of Idaho fescue (Festuca idahoensis) and the understory of Community 1.2 is dominated by bluebunch wheatgrass (Pseudoroegneria spicata). Community 1.1 is more predominant at sites closer to the higher end of the relative effective annual precipitation range (15 to 19 inches) as Idaho fescue is better adapted to slightly wetter conditions (Zouhar, 2000). In Community 1.3, a shift from a mountain big sagebrush-dominated overstory to a more diverse shrub overstory occurs. Bunchgrasses (Idaho fescue and bluebunch wheatgrass) remain the dominant understory. The characteristics of the Steep Loamy 15 to 19 inch ecological site allow for relatively high productivity and diversity in both the overstory and understory relative to many other ecological sites within the Lost River Mountain LRU.
Processes (both natural and anthropogenic) that can result in state and community changes include frequent or severe fire, grazing that results in chronic defoliation, and land use changes (Davies et al., 2011).
Characteristics and indicators
The shift between communities at this ecological site is primarily driven by slight variations in local abiotic conditions. Shift in the understory composition from Idaho fescue to bluebunch wheatgrass is usually attributed to available moisture. Although Idaho fescue can be present closer to the 15 inch end of the relative effective annual precipitation range, bluebunch wheatgrass is better adapted to these conditions and tends to occupy a greater percentage of the canopy (Zouhar, 2000).
Shift from an overstory canopy dominated by mountain big sagebrush to a mixed shrub overstory can result from slightly localized abiotic factors such as depth to bedrock and coarse fragment volume on the surface and throughout the soil profile. Biotic conditions including distance from seed source and resource competition can also play a role.
Resilience management
This site has moderate to high resilience as a result of the cryic 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 cryic (cold) temperature regime and xeric (wet) moisture regime tend to have higher diversity, high production, and are therefore more resilient. This is specifically true 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 post-disturbance invasion due to the biodiversity generally present at the site. Sites with high biodiversity have been shown to exhibit increased resistance and resilience as a result of the differential impact of disturbances such as insects, disease, and fire on the variety of species present (Oliver et al., 2015).
Submodel
Description
The Disturbed state is a result of both natural and anthropogenic disturbance events that result in widespread sagebrush mortality at a given site. The primary natural disturbance resulting in sagebrush mortality at this ecological site is frequent or severe wildfires; however, intense freeze events, insect damage, and disease can also occur. Both mountain big sagebrush and basin big sagebrush are particularly susceptible to stand-replacing fires and often experience complete canopy loss during moderate and severe wildfire events (Innes, 2017; Tirmenstein, 1999).
Because this LRU exists primarily on publicly managed lands (US Forest Service, Bureau of Land Management, and State of Idaho), 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 or chronic defoliation of vegetation.
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 post-fire disturbance 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 a near complete loss of overstory sagebrush species, often replaced by shrub species that can take advantage of the local disturbance regime such as threetip sagebrush (Artemisia tripartita) and yellow rabbitbrush (Chrysothamnus viscidiflorus). A shift towards an increase in native and disturbance-tolerant grasses and forbs is likely with the removal of resource competition associated with the sagebrush overstory presence. Severe disturbance events also increase the opportunity for invasion of annual grasses and weeds such as cheatgrass (Bromus tectorum) and thistle species. The canopy cover percentage of these species is usually dependent on the distance of a seed source but mostly stays under five 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 are established quickly and reach a representative canopy within 10 years post-disturbance. These species continue to increase until the overstory canopy of sagebrush begins to return. However, local resilience of these sites 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 invasion. The greater the establishment of invasives, the lower the site resilience becomes.
Submodel
Description
When a Steep Loamy 15 to 19 inch site enters the Degraded state, it is generally a result of post-disturbance invasion by invasive species. This state can be driven by a particularly severe disturbance either in the form of fire, intensive grazing, or land use, or repeated disturbances of low to moderate severity over short periods. Proximity to a seed source as well as seed transport vectors play a role in the 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 mountain big sagebrush and other shrubs will also decrease. These openings in the canopy will generally 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 spp.). Continued disturbance will increase the cover and production of these species. Productivity and canopy cover are 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 the ability to rapidly establish when competition from native vegetation has been removed through disturbance. Additionally, cheatgrass can 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
The transition from the Reference state to the Disturbed state is a result of both natural and anthropogenic disturbance regimes. The primary disturbance regime likely to impact this ecological site is moderate to severe fire occurrence. Fire return intervals in the reference communities are often driven by the dominant understory species. This can be less than 30 years in bluebunch wheatgrass communities and 15 years for Idaho fescue (Innes 2017; Zouhar, 2000).
Constraints to recovery
The primary constraint to recovery is the distance to a seed source. Most fire events are fatal to mountain big sagebrush and when the disturbance is severe enough and the extent is large, 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 period can be greatly reduced through seeding and planting interventions.
Bluebunch wheatgrass is resistant to fire and generally unharmed in all but the most severe events. Idaho fescue is less resistant, increasing the time needed to return to pre-disturbance levels.
Context dependence
The primary factors driving the likelihood of restoration success are post-disturbance weather patterns and distance from natural seed sources. Prolonged periods of drought can slow restoration processes, whereas average to above-average precipitation following the disturbance can greatly increase speed and success in the re-establishment of sagebrush species (Robin 2017; Steinberg 2002; Fryer 2009).
Mechanism
The transition from the Reference state to the Degraded state is a result of a disturbance event (or multiple disturbance events) followed by the establishment of invasive species, primarily cheatgrass. The likelihood of this transition increases when multiple disturbance events occur with little time for recovery, or following especially severe disturbance events.
Constraints to recovery
Once cheatgrass begins to establish on a site, it can grow and reproduce rapidly often forming a monoculture (Zouhar, 2003). Once established, complete removal of the species from a site is difficult, costly, and resource intensive, limiting restoration options. Success is increased by identifying sites early in the transition and beginning treatment before cheatgrass populations become significant.
Mechanism
The most important mechanism driving restoration from the Disturbed state to the Reference state is time without a sagebrush removing disturbances and distance from overstory species (sagebrush) seed source. Seeding or planting of desired overstory species in the Reference state can speed restoration efforts.
Context dependence
Restoration is highly dependent on time without disturbance. New sagebrush seedlings that can establish on a site are moderately sensitive to disturbances such as freeze-kill, insect damage, 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 the 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
The transition from the Disturbed state to the Degraded state is more likely than a direct transition from the Reference to the Degraded state. The transition occurs when a disturbance removes most or all of the native shrub overstory and grass understory, creating available space for invasive species establishment. Once established, many invasive species such as cheatgrass can promote feedback loops that increase their dominance over time.
Constraints to recovery
The primary constraint to recovery is the successful removal of invasive species. Once established, the successful removal of cheatgrass and other invasive species is a resource-intensive process. Time without disturbance and seeding/planting interventions of native vegetation can aid in recovery.
Context dependence
Factors that contribute to restoration success include the level of invasive species establishment, intervention methods, and post-treatment weather patterns. A prolonged period of drought can slow restoration processes, whereas average to above-average precipitation post-disturbance can greatly increase speed and success in the re-establishment of sagebrush species (Robin, 2017; Steinberg, 2002; Fryer, 2009).
Mechanism
The most important factor in restoration from the Degraded state to the Disturbed state is the removal of invasive annual grasses and the re-establishment of native grasses. Depending on the level of invasive species presence, this may only be achieved using mechanical interventions and seeding.
Context dependence
Restoration is dependent on time without disturbance and favorable planting conditions. 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 the restoration period. Periods of drought will slow the process significantly, whereas periods of above-normal precipitation aid in sagebrush and bunchgrass regeneration and establishment (Innes 2017; Steinberg 2002; Fryer, 2009).
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