State 1
Reference

The Reference state consists of three dominant plant communities: a little sagebrush (Artemisia arbuscula ssp. longiloba) dominated community, a black sagebrush (Artemisia nova) dominated community, and a community where overstory shrub canopy dominance consists of big sagebrush species, primarily mountain big sagebrush (Artemisia tridentata spp. vaseyana). The greatest difference between the three plant communities is the composition and foliar cover of sagebrush species. Generally, mountain big sagebrush foliar cover increases on sites that are closer to the higher end of the effective precipitation range (15 to 19 inch) or the calcium carbonate concentration in the soil is lower, closer to the minimum 15 percent required in the site concept. This community also occurs more often when calcareous soil presence is deeper in the soil profile, closer to a depth of 20 inches (50cm). Processes (both natural and anthropogenic) that can result in state and community changes include fire, grazing, land use change, and establishment of invasive species (Davies et al., 2011).

Characteristics and indicators. The shift between plant communities at this site is generally driven by calcium carbonate concentration in soils, effective precipitation, and sagebrush-killing disturbances or lack thereof. 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, and Bowerstock, 2020; Knick et al., 2005). Improper grazing practices can also lead to an increase in sagebrush canopy cover and an increased risk of severe, stand-replacing fire occurrence. Removal of understory grasses can lessen the opportunities for low severity fire occurrence 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 cryic soil temperature regime and xeric soil moisture regime. Resistance and resilience of a specific site have been attributed with 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). Although both black sagebrush and little sagebrush species are both susceptible to fire damage and usually killed by fire events, fire events within these communities are usually rare. These communities generally lack the fine fuels required to carry fire, promoting relatively infrequent fire return intervals (Steinberg, 2002). Mountain big sagebrush is also highly susceptible to damage and mortality from fire events. These communities also tend to have higher fuel loading and carry fire more easily and frequently than in the black and little sagebrush communities (Innes, 2017).

Community 1.1
Little Sagebrush and Bluebunch Wheatgrass

Figure 9. Little Sage/Bluebunch Wheatgrass community

Community 1.1 is well adapted to the abiotic conditions of the Lost River Mountain LRU. Both little sagebrush (Artemisia arbuscula) and black sagebrush (Artemisia nova) have adaptations that allow them to thrive on the highly calcareous soils that form from limestone parent material. Little sagebrush more often dominates the canopy at this ecological site; however, it is not uncommon for the percent composition between black sagebrush and little sagebrush to be nearly equal. It is also possible that one of the two species is missing from the canopy completely. Black sagebrush prefers conditions where the highly calcareous soils are closer to the surface. Because the depth to calcareous soils in the Loamy Calcareous ecological site is 10 inches (25cm), little sagebrush can outcompete black sagebrush (McArthur & Stevens, 2009; Tilley & St. John [2], 2012). Therefore, little sagebrush has a higher canopy cover (35 percent) and contributes more volume to overall ecological site production value. Little sagebrush/Bluebunch Wheatgrass communities can form in a mosaic distribution with other communities in this state (1.1 & 1.3) across the range of relative effective annual precipitation. As effective precipitation increases, the understory of bluebunch wheatgrass (Pseudoroegneria spicata) decreases in percent canopy cover. Other bunchgrasses such as Idaho fescue (Festuca idahoensis) increase in canopy cover as available moisture increases. Production in this community is lower than in other communities because of the low sagebrush overstory. Production ranges from 350 to 750 pounds per acre, averaging 550 pounds per acre. Shrub species contribute 200 to 445 pounds per acre, while grasses contribute 120 to 230 pounds per acre. Little sagebrush species account for up to 30 percent of the canopy cover, while bluebunch wheatgrass can reach 20 percent canopy cover.

Resilience management. Resilience is moderate in Community 1.1. Black sagebrush and little sagebrush are both drought-tolerant species able to withstand periods of below-average precipitation. Bluebunch wheatgrass is well suited to the variable climate experienced in the Lost River Mountains and is resilient to many natural disturbances including drought and fire. Bluebunch wheatgrass has been shown to recover to pre-fire disturbance population levels in one to seven years post-disturbance. Under certain conditions, canopy cover and production can exceed pre-fire values (Zlatnik, 1999). Bluebunch wheatgrass is a decreaser, reducing canopy cover and production in relation to grazing pressure. Under heavy grazing pressure, the species will shift towards areas such as under the canopy of shrubs, opening the canopy for the establishment of rhizomatous grass species, invasive species, or bare ground.

Community 1.2
Little Sagebrush and Mixed Bunchgrass

Figure 11. Little Sagebrush/Mixed Bunchgrass community

Community 1.2 has a mixed low sagebrush overstory (little sagebrush and black sagebrush) and a mixed bunchgrass understory (Idaho fescue and bluebunch wheatgrass). The primary difference between Community 1.1 and 1.2 is the addition of Idaho fescue and to a lesser extent, Geyer's sedge (Carex geyeri) in the understory composition. This community occurs towards the upper end of the 15 to 19 inch relative effective annual precipitation range of the site. Both bluebunch wheatgrass and Idaho fescue thrive in the loamy soil textures of the Loamy Calcareous ecological site. Ideal conditions for Idaho fescue includes soils that lack carbonates or the carbonates are deeper in the soil. Additionally, Idaho fescue prefers slightly higher amounts of relative effective annual precipitation than the other grass species found at this ecological site (Zouhar, 2000). Understories dominated by Idaho fescue become more predominant on the upper end of the 15 to 19 inch climatic subset. Production in Community 1.2 ranges from 300 to 792 pounds per acre, averaging 610 pounds per acre. Canopy cover by functional group can be as high as 33 percent for shrubs, 36 percent for grasses, and 13 percent for forbs.

Resilience management. Resilience is moderate in Community 1.2. Black sagebrush and little sagebrush are both drought-tolerant species able to withstand periods of below-average precipitation. Bluebunch wheatgrass is well suited to the variable climate in the Lost River Mountains and is resilient to many natural disturbances including drought and fire. Having Idaho fescue as a co-dominant understory species adds diversity and with that diversity, increased resilience from insect and disease disturbances.

Community 1.3
Bluebunch Wheatgrass and Mountain Big Sagebrush

Figure 14. Bluebunch Wheatgrass/Mountain Big Sagebrush community

Figure 15. Canopy Cover Percent By Plant Functional Group (Tier III Data)

The Bluebunch Wheatgrass and Mountain Big Sagebrush community is well adapted to the abiotic conditions of the Lost River Mountain LRU. Mountain big sagebrush can occur on Mollisols, Aridisols, and Inceptisols, however, is most abundant on Mollisols (Innes, 2017). Mountain big sagebrush increases in canopy cover as highly calcareous soils are found deeper in the soil profile, which often coincides with a slight increase in relative effective annual precipitation. As seen in this community, mountain big sagebrush can form dense monocultures with little competition from other shrub species. The understory is dominated by bunchgrasses, primarily bluebunch wheatgrass, and to a lesser extent at the higher end of the effective precipitation range, Idaho fescue (Festuca idahoensis). Plant diversity in bluebunch wheatgrass/mountain big sagebrush-dominated communities is higher than with any other big sagebrush species. This is primarily due to high diversity in forb and grass understory species (Innes, 2017). Total annual production of Community 1.3 ranges from 550 to 1,100 pounds per acre, averaging 850 pounds per acre. Shrub canopy cover can be as high as 28 percent, with 23 percent comprised of mountain big sagebrush. Grass canopy cover can exceed 50 percent, the majority consisting of bluebunch wheatgrass, Idaho fescue, and Sandberg bluegrass (Poa secunda). Forb canopy cover can reach 22 percent, but is more often closer to 10 percent.

Resilience management. This community has moderately low resilience. Mountain big sagebrush is the least drought tolerant of the big sagebrush species. Mountain big sagebrush is highly flammable and fire typically kills plants within the disturbance area. Because this species reproduces via seed that is dispersed through wind, water, and zoochory, distance from a viable source population plays a major role in post-disturbance regeneration. When disturbance events cover a large area spatially, the regeneration timespan increases and the likelihood of transitioning to another state or community increases (Innes, 2017). Slow regeneration can open windows for erosion to occur and invasive species to establish. Post-disturbance seeding and planting can increase restoration success. Bluebunch wheatgrass is a much more resilient species to the local disturbance regimes. The species is drought tolerant and usually is not killed except during the most severe wildfire events. During severe disturbances that remove the sagebrush overstory, bluebunch wheatgrass can persist as the dominant vegetation on this ecological site (Zlatnik, 1999). When Idaho fescue is the dominant understory or shares dominance in the 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 fire events prompt a shift into the Disturbed state. The additional effective precipitation received at this site (15 to 19 inch) adds resilience. Available moisture has been shown to be a key component of successful post-disturbance recovery (Chamber et al., 2014).

Pathway 1.1A
Community 1.1 to 1.2

Little Sagebrush and Bluebunch Wheatgrass

Little Sagebrush and Mixed Bunchgrass

The primary driver that differentiates Community 1.1 and Community 1.2 is a slight increase in relative effective annual precipitation (REAP). When a Loamy Calcareous ecological site exists at the upper end of the 15 to 19 inch climatic subset, Idaho fescue is more likely to occupy a significant portion of the understory canopy. Idaho fescue prefers slightly higher volumes of effective precipitation and increases in canopy cover and production values accordingly (Zouhar, 2000).

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 1.1B
Community 1.1 to 1.3

Little Sagebrush and Bluebunch Wheatgrass

Bluebunch Wheatgrass and Mountain Big Sagebrush

The transition from Community 1.1 to 1.3 is a product of higher volumes of REAP and slight changes in soil characteristics. Of all the big sagebrush species, mountain big sagebrush prefers sites with higher available moisture. Mountain big sagebrush thrives in deep soils that lack shallow concentrations of calcium carbonates (Innes, 2017). As carbonates are pushed deeper into the soil profile, conditions become more ideal for mountain big sagebrush dominance. Likewise, Idaho fescue increases in the understory with increased REAP, closer to 19 inches (Zouhar, 2000).

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

State 2
Disturbed

Figure 18. Loamy Calcareous 15-19 Inch Ecological Site in the Disturbed State

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 wildfire; however, flooding, intense freeze events, and insect and disease can also occur. Mountain big sagebrush is highly 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 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. 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. 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 the possibility of post-disturbance invasion. The greater the establishment of invasives, the lower the site resilience becomes

Community 2.1
Rabbitbrush and Bunchgrass

The Rabbitbrush and Bunchgrass 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 removal disturbance at this ecological site is frequent or severe fire. The frequency and severity of these fire disturbances are highly influenced by the overstory composition of the specific site in the Reference state, before disturbance. The composition and extent of the sagebrush species in the overstory impacts that respective fire regime. Communities in the Reference state with 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. In Community 2.1, the overstory is comprised of disturbance-tolerant shrubs at a reduced canopy. The primary overstory species include yellow rabbitbrush (Chrysothamnus viscidiflorus) and threetip sagebrush (Artemisia tripartita). Bunchgrasses, primarily bluebunch wheatgrass (Pseudoroegneria spicata), Idaho fescue (Festuca idahoensis) and Sandberg bluegrass (Poa secunda) primarily occupy the understory. Canopy cover of bunchgrasses is often higher early in the successional period following a disturbance, decreasing as the yellow rabbitbrush or threetip sagebrush canopy increases.

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 can 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 can 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 threetip sagebrush 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).

Transition T1A
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 flooding events, 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 distance from a viable seed source. Disturbances that cover a larger extent increase the 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 re-establishment of sagebrush species (Robin, 2017; Steinberg, 2002; and Fryer, 2009).

Restoration pathway R2A
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).