State 1
Reference

The Reference State of the 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 spp. vasayana) overstory. 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 closer to the higher end of the effective precipitation range (15 to 19 inches) as Idaho fescue is better adapted to slightly wetter conditions (Zouhar, 2000). Community 1.3 occurs more often in valley or drainage bottoms where sandy loam soil textures are more prevalent. The community is comprised of a basin big sagebrush dominated overstory with a mixed perennial grass understory. The characteristics of the Loamy 15 to 19-inch ecological site allow for high productivity and diversity in the overstory and understory relative to other ecological sites within the Lost River Mountain LRU. Processes (natural and anthropogenic) that can result in state and community changes include frequent or severe fire occurrence, 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 effective 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 basin big sagebrush can be attributed to changes in soil texture and landform. Basin big sagebrush tends to dominate when soil texture conditions shift to sandy or silty loams and/or landforms that include floodplains, low stream terraces, and drainages (Tirmenstein, 1999).

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 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 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 insect, disease, and fire on the variety of species present (Oliver et al., 2015).

Community 1.1
Mountain Big Sagebrush and Idaho Fescue

Figure 10. Loamy reference site in the North end of the Lemhi range.

The mountain big sagebrush and Idaho fescue community is well adapted to the abiotic conditions found at this ecological site in the Lost River Mountain LRU. Both species thrive in loamy soil textures that lack carbonates, and high volumes of coarse fragments and occur on slopes less than 30 percent. Idaho fescue prefers slightly higher amounts of effective precipitation than the other grass species found at this ecological site. Understories dominated by this species become more predominant on the upper end of the 15 to 19-inch climatic subset (Zouhar, 2000). Of the big sagebrush sub-species, mountain big sagebrush has the greatest preference for sites with higher soil moisture availability. The species is commonly found on moderately deep to deep well-drained Mollisols, and at higher elevations than other big sagebrush species (Innes, 2017). In this community, mountain big sagebrush tends to exist as a monoculture in the overstory, however, other species of shrubs may be present at less than five percent canopy cover. Production in this community is high, ranging from 800 to 1,600 pounds per acre, with an average of just over 1,000 pounds per acre. Mountain big sagebrush foliar cover averages 24 percent, while Idaho fescue averages 22 percent. Species of lupine (Lupinus sp.) and sulfur flower buckwheat (Eriogonum umbellatum) each average six percent canopy cover respectively.

Resilience management. With mountain big sagebrush being the primary overstory species, this community in the reference state exhibits low to moderate resilience. Mountain big sagebrush is drought intolerant. Sagebrush foliage is highly flammable and because they are among the most productive of sagebrush species, fuel loading and continuity are higher (Innes, 2017). This increases susceptibility to severe wildfire events at more frequent intervals which can slow recovery. Fires in mountain big sagebrush communities tend to be stand replacing and under poor post-disturbance conditions, recovery to pre-fire levels can exceed 75 years. When Idaho fescue is the dominant understory, fire return intervals can be as frequent as 10 to 15 years. Although Idaho fescue fares better than mountain big sagebrush during fire events, mortality averages between 20 and 50 percent and can exceed 75 percent after severe events (Zouhar, 2000). Severe or frequent fire events prompt a shift into the Disturbed State. The effective precipitation received at this site (15 to 19-inch) adds resilience. Available moisture has shown to be a key component of successful post-disturbance recovery (Chamber et al., 2014).

Community 1.2
Mountain Big Sagebrush and Bluebunch Wheatgrass.

The mountain big sagebrush and bluebunch wheatgrass community is most prevalent on the lower end of the 15 to 19-inch climatic subset of the Loamy ecological site. Bluebunch wheatgrass is able to thrive under a broad range of moisture conditions and is one of the most drought-resistant native bunchgrasses (Zlatnik, 1999). These adaptations often allow bluebunch wheatgrass to become the dominant understory at the drier sites in the 15 to 19-inch climatic subset. Although both Idaho fescue and bluebunch wheatgrass populations can be present in this community, canopy cover and percentage of total production will be higher for bluebunch wheatgrass. Mountain big sagebrush remains the dominant overstory species. Other shrub species that may be present at a limited canopy cover include mountain snowberry (Symphoricarpos oreophilus), yellow rabbitbrush (Chrysothamnus viscidiflorus), and spineless horsebrush (Tetradymia canescens). Production in this community is high, ranging from 800 to 1,600 pounds per acre, with an average of 1,100 pounds per acre. Mountain big sagebrush foliar cover averages 28 percent. Bluebunch wheatgrass averages 23 percent. Idaho fescue is sub-dominant in the understory averaging 15 percent canopy cover. Species of lupine (Lupinus sp.) and phlox (Phlox sp.) each average three percent canopy cover.

Resilience management. With mountain big sagebrush being the primary overstory species, this community exhibits low to moderate resilience. Of all the big sagebrush sub-species, mountain big sagebrush is the least drought tolerant. Sagebrush foliage is highly flammable and because they are among the most productive of sagebrush species, fuel loading and continuity are higher (Innes, 2017), increasing susceptibility to severe wildfire events at more frequent intervals which can slow recovery. Fires in mountain big sagebrush stands tend to be stand replacing and under poor conditions, recovery to pre-fire levels can exceed 75 years (Innes, 2017). Bluebunch wheatgrass has a higher survival rate because growth points are protected. Fire return intervals are generally less than 30 years depending on overstory and related vegetation. Recovery of bluebunch wheatgrass from fire is rapid, returning to pre-disturbance populations in less than five years (Zlatnik, 1999). Although bluebunch wheatgrass populations may survive severe fire events, if the mountain big sagebrush overstory is removed, this can prompt a shift into the Disturbed State. The volume of effective precipitation received at this site (15 to 19-inch) adds resilience. Available moisture has shown to be a key component of successful post-disturbance recovery (Chamber et al., 2014).

Community 1.3
Basin Big Sagebrush/Mixed Perennial Grass

The basin big sagebrush (Artemisia tridentata spp. tridentata) mixed perennial grass community occurs within the Loamy 15 to 19 Inch Precipitation Zone ecological site under specific localized landform and soil conditions. Basin big sagebrush establishes well in deep, sandy loam soils that exist within valley and drainage bottoms, in or near floodplains, and portions of stream terraces of the Loamy ecological site. The species does well at the drier end of the 15 to 19-inch effective precipitation range, able to take advantage of deep moisture accumulations in the soil (Tirmenstein, 1999). Canopy cover shifts to mountain big sagebrush as distance increases from these respective landforms and conditions. The understory is a mix of perennial grass species, bluebunch wheatgrass being the most predominant. Forb composition and canopy cover are similar to the other two communities in this state. Production values in this community range from 700 to 1,100 pounds per acre, averaging 850 pounds per acre. The species that contribute the most to overall production values include basin big sagebrush, bluebunch wheatgrass, and mountain big sagebrush.

Resilience management. The basin big sagebrush/mixed perennial grass community is impacted by three primary disturbance regimes; severe or frequent fire, grazing that results in chronic defoliation, and periodic drought that stresses vegetation and can result in mortality. The community has low to moderate resilience to fire, and moderate resilience to grazing and drought. Under most circumstances, basin big sagebrush mortality is very high following a fire disturbance event and fire return intervals range between 15 and 70 years. However, basin big sagebrush produces a high volume of seeds annually with high germination rates. If a nearby population exists post-disturbance, recovery time can be greatly reduced (Tirmenstein, 1999). Bluebunch wheatgrass has a high survival rate because its growth points are protected. Fire return intervals are generally less than 30 years depending on overstory and related vegetation. Recovery of bluebunch wheatgrass from fire is rapid, returning to pre-disturbance populations in less than five years (Zlatnik, 1999). Although bluebunch populations may survive severe fire events, if the mountain big sagebrush overstory is removed, this can prompt a shift into the Disturbed State. Moderate, long-term grazing has shown to have a minor impact overall on basin big sagebrush overstory; however, understory grasses such as bluebunch wheatgrass can become more vulnerable to other disturbances as a result (Davies et al., 1998). Basin big sagebrush is able to take advantage of deep available soil moisture and bluebunch wheatgrass is well adapted to low and variable annual precipitation. This allows both species to function relatively well under drought conditions (Tirmenstein, 1999 & Zlatnik, 1999).

Pathway P1-2
Community 1.1 to 1.2

Mountain Big Sagebrush and Idaho Fescue

Mountain Big Sagebrush and Bluebunch Wheatgrass.

The transition from Community 1.1 to Community 1.2 is primarily driven by localized effective precipitation. Bluebunch wheatgrass is able to outcompete Idaho fescue at the lower end of the 15 to 19-inch effective precipitation range, allowing it to become the dominant understory species. When conditions are slightly wetter, Idaho fescue establishes well and can dominate the understory composition. Mountain big sagebrush functions well in both communities as the dominant overstory species.

Context dependence. The abiotic conditions that result in community transitions from Community 1.1 to 1.2 are site-specific and not directly influenced by anthropogenic or biotic interactions.

Pathway P1-P3
Community 1.1 to 1.3

Mountain Big Sagebrush and Idaho Fescue

Basin Big Sagebrush/Mixed Perennial Grass

The transition from community 1.1 to 1.3 is a result of localized abiotic conditions surrounding landform and soil properties. The overstory composition dominated by Basin big sagebrush in community 1.3 indicates that soils have transitioned to sandy and silty loams. Basin big sagebrush prefers deep, sandier soils across the 15 to 19-inch precipitation range and because of these preferences, these communities often occur along drainages, valley bottoms, and floodplain steps. The understory in this community can be dominated by either bluebunch wheatgrass or Idaho fescue, but tends to be more diverse in grasses than in Community 1.1.

Context dependence. The abiotic conditions that result in transitions from Community 1.1 to 1.3 are site specific and not directly influenced by anthropogenic or biotic interactions.

State 2
Disturbed

Figure 17. Grazed site with a mixed overstory of threetip sagebrush, basin big sagebrush, and rabbitbrush.

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 severe or frequent wildfire; however, intense freeze events and insect and disease can also occur. Both mountain big sagebrush and basin big sagebrush are particularly susceptible to stand-replacing fires and often experiences 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), 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. 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, intense grazing that results in significant defoliation post-fire disturbance can increase bare ground cover, increase erosion potential, and slow the reestablishment of native 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 are able to take advantage of the local disturbance regime. Common replacement species include Artemisia tripartita (threetip sagebrush) and Chrysothamnus viscidiflorus (yellow rabbitbrush). 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 post-disturbance, 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 establish quickly and reach a representative canopy within 10 years post-disturbance. Grasses and shrubs 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. Recovery can be impacted by the quantity of immediate post-fire precipitation (Zlatnik, 1999). More severe disturbances increase possibility of post-disturbance invasion. The greater the establishment of invasives, the lower the site resilience becomes.

Community 2.1
Bunchgrass and Yellow Rabbitbrush

The bunchgrass and yellow rabbitbrush community is driven by the disturbance related removal of the primary overstory of sagebrush species. Both natural and anthropogenic disturbances that result in near complete removal of the sagebrush overstory create opportunities for increased establishment of both native and non-native grasses and forbs, as well as disturbance tolerant shrubs. In this community, the primary sagebrush removing disturbance at this ecological site is severe or frequent fire. The frequency and severity of these fire disturbances are highly influenced by the overstory composition of the specific site in the reference state prior to disturbance. The composition and extent of the sagebrush species in the overstory impacts that respective fire regime. Communities in the Reference State with either a basin or mountain big sagebrush overstory are highly susceptible to stand-replacing fire events with fire return intervals ranging from five to 70 years (Innes, 2017 & Termenstein, 1999). This increases the likelihood of transition from the Reference State to the Disturbed State (community 2.1) following fire disturbances.

Resilience management. This plant community is moderately resilient because the grasses and forbs that dominate the composition are resistant to a variety of disturbances and able to re-establish quickly in the event of more severe disturbances. Both bluebunch wheatgrass (Pseudoroegenaria spicata) and Sandberg bluegrass (Poa secunda) are rarely harmed by fire events except for in the most severe instances. Both plants are able to reduce the amount of heat transfer to the root systems, allowing successful regrowth (Zlatnik, 1999 & Howard, 1997). Studies show that in the absence of grazing, bluebunch wheatgrass-dominated systems are able to return to pre-fire production levels eight years post-disturbance (Zlatnick, 1999). Sandberg bluegrass has been shown to fully re-establish post-plowing events in as little as 7 years (Howard, 1997). Idaho fescue (Festuca Idahoensis) is less resilient to both fires and grazing. Idaho fescue can often survive low severity fires, however, moderate to severe fires are more destructive, resulting in a 30-year return to pre-disturbance canopy cover (Zouhar, 2000). Both yellow rabbitbrush and rubber rabbitbrush (Ericameria nauseosa) are often the first shrub species to re-establish on this ecological site following a disturbance and can increase in relation to the severity or frequency of the disturbance. Although yellow rabbitbrush can exist in relatively small numbers within the Reference State, it becomes the dominant shrub species in highly disturbed systems (Terminstein, 1999).

Community 2.2
Threetip Sagebrush and Mixed Perennial Grass

Figure 20. Heavily grazed site on the Southern end of the Lost River Range

The threetip sagebrush and mixed perennial grass Community is a disturbance impacted community driven by moderate to high grazing pressure that results in chronic defoliation and/or hoof related disturbances. This community is marked by at least a five percent canopy cover of threetip sagebrush which is disturbance tolerant, though may not be the dominant canopy cover. Basin big and mountain big sagebrush may also be present in the canopy at varying densities. The understory is a mix of perennial grasses dominated by Sandberg bluegrass (Poa secunda) and bluebunch wheatgrass. The canopy cover of these species can vary based on grazing pressure impacts (timing, frequency, intensity, duration). Forb cover is usually less dense and less diverse than the Reference State. Invasive species such as cheatgrass (Bromus techtorum) and non-native thistle can also be present at canopy covers of less than five percent. Overall production for this community is lower than all communities in the Reference State, primarily due to the loss of dominance by either bluebunch wheatgrass or Idaho fescue, both of which contribute significantly to overall production in the Reference State. Production values range from 400 to 900 pounds per acre, averaging 650 pounds per acre.

Resilience management. This community has low to moderate resilience. As grazing pressure increases, the the composition of the understory changes. Herbivory and hoof-related disturbance open opportunities for the immigration of invasive species, some of which can significantly alter ecosystem dynamics. Certain studies have shown that although the composition and density of plant species may remain intact over long periods under moderate grazing pressure, the community becomes more susceptible to impacts of other disturbance regimes such as wildfire (Davies et al. 2018).

Pathway P1-2
Community 2.1 to 2.2

Community 2.1 is driven by wildfire disturbance, whereas community 2.2 is driven by grazing pressure that results in chronic defoliation. The dynamics of the transition from Community 2.1 to 2.2 would greatly depend on the stage of fire recovery following the disturbance event. If the sagebrush or shrub overstory has not recovered and heavy grazing is introduced, community 2.2 will present (and be maintained) with little shrub overstory canopy cover. If the shrub overstory has recovered, the impact will primarily be on the understory grass species.

Context dependence. The outcome of a shift from Community 2.1 to 2.2 is heavily dependent on grazing variables including timing, duration, frequency, intensity, and what period of recovery the initial community was in.

Pathway P2-1
Community 2.2 to 2.1

The transition from Community 2.2 to 2.1 is a result of severe or frequent wildfire disturbance event. When a moderate to severe wildfire occurs, overstory sagebrush canopy is removed and canopy cover and composition of the grass and forb understory can be greatly altered. Recovery timeframes can vary based on initial plant composition, distance from seed source, post-disturbance weather patterns, grazing strategies, and the addition of any post-disturbance seeding or planting efforts.

Context dependence. Moderate grazing regimes that result in chronic defoliation over extended periods of time can alter ecological dynamics and change the fire ecology of an ecological site. Increases in the abundance of fire prone invasive species such as cheatgrass (Bromus techtorum) and changes in grass structure can shorten fire return intervals and result in more severe disturbances (Davies et al., 2018). Fire disturbance events must be severe enough to remove the majority of the overstory canopy for the transition to occur.

Transition T1-2
State 1 to 2

Reference

Disturbed

Transition from the Reference to the Disturbed State is a mechanism of moderate to severe disturbance, both natural and anthropogenic. The most likely disturbance to cause this transition is wildfire. Other disturbances include but are not limited to freeze kill events, insect and disease, overgrazing, and mechanical brush removal.

Constraints to recovery. The primary constraint to recovery is the distance to a seed source and time. When the disturbance is severe 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. Re-establishment to pre-disturbance canopy cover and extent of mountain big sagebrush cover generally exceeds 25 years even in ideal conditions (Innes, 2017). This time period can be greatly reduced through seeding and planting interventions.

Context dependence. The primary factors driving the likelihood of restoration success are post-disturbance weather patterns and the distance from viable seed sources. Disturbances that cover a larger extent increase distance to seed sources. Prolonged periods of drought can slow restoration processes. Alternately, average to above-average precipitation post-disturbance can greatly increase speed and success in the re-establishment of sagebrush species (Robin, 2017; Steinberg, 2002; and Fryer, 2009).

Restoration pathway R2-1
State 2 to 1

Disturbed

Reference

The most important mechanism driving restoration from the disturbed state to the reference is time without sagebrush removing disturbance. Distance from overstory species (sagebrush) seed source can also impact the speed of restoration. Seeding or planting of desired overstory species found in the Reference state can speed restoration efforts.

Context dependence. Restoration is highly dependent on time without disturbance. New sagebrush seedlings are moderately sensitive to disturbances such as flood, freeze, and insect and disease. They are highly sensitive to herbivory and even low-severity fire events (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).