State 1
Reference State

The Reference state consists of three dominant plant communities: The curl-leaf mountain mahogany and black sagebrush (Artemisia nova) dominated community, the mixed shrub overstory community (1.2) which can include curl-leaf mountain mahogany, mountain big sagebrush (Artemisia tridentata ssp. vaseyana), low sagebrush (Artemisia arbuscula) and black sagebrush (Artemisia nova), and the wooded mountain mahogany community which can include Douglas fir (Pseudotsuga menziesii), Rocky Mountain juniper (Juniperus scopularum), and limber pine (Pinus flexus). The understory in both communities is dominated by bluebunch wheatgrass but can include a variety of other bunch and rhizomatous grasses at a lesser canopy cover. The primary difference between the two communities is the composition and foliar cover of shrub species. Foliar cover of other shrub species increases in relation to openings not already occupied by curl-leaf mountain mahogany. Processes (both natural and anthropogenic) that result in state and community changes include fire, grazing, land use change, and the occurrence of invasive species.

Characteristics and indicators. The shift between communities in the Reference state is driven by curl-leaf mountain mahogany canopy cover. Well-established stands of mountain mahogany can be dense and prevent any future establishment of other shrub species, primarily sagebrush. Likewise, less dense canopies of mountain mahogany present less competition and create opportunities for other species to establish in their absence. Low-severity disturbances are the primary driver for decreasing the canopy cover of mountain mahogany and creating opportunities for other species to establish. Severe disturbances such as fires that are stand-replacing and destroy the seed bank could lead to a shrub community not dominated by curl-leaf mountain mahogany.

Resilience management. The Reference state is overall moderately resilient. In well-established communities, resilience towards climatic disturbances such as drought is high. Curl-leaf mountain mahogany is adapted to dry conditions and is able to take advantage of moisture funneled to cracks in the bedrock. Resilience to low-severity fire is high; however, severe stand-replacing fire, which removes any nearby seed source, can take several decades to recover from (Gucker, 2006).

Community 1.1
Curl Leaf Mountain Mahogany/Bluebunch Wheatgrass Community

The Mountain Mahogany/Bluebunch Wheatgrass community is well adapted to the specific conditions found at the Rocky Hills ecological site. This community is dominated by an overstory of curl-leaf mountain mahogany and an understory dominated by bunchgrasses, primarily bluebunch wheatgrass (Pseudoroegneria spicata). The canopy density of curl-leaf mountain mahogany of this community can vary by site but can be as dense as 35 percent. On sites where curl-leaf mountain mahogany is less dense, a mixture of other shrubs fills in the canopy gaps. These species can include mountain big sagebrush, black sagebrush (Artemisisa nova), yellow rabbitbrush (Chrysothamunus viscidiflorus), and little sagebrush (Artemisia arbuscula). The forb population can be quite diverse and includes long leaf phlox (Phlox longifolia), spiny phlox (Phlox hoodii), granite prickly phlox (Linanthus pungens), Indian paintbrush species (Castilleja sp.), flax species (Linum sp.), and stemless mock goldenweed (Stenotus acaulis). Production in this community is weighted towards the shrub overstory, specifically, curl-leaf mountain mahogany. Production is 530 to 725 pounds per acre, with an average of 625 pounds per acre.

Resilience management. This community has low to moderate resilience. Although very resistant to drought and frequent or high-severity fires, this community has difficulty recovering when much of the overstory is eliminated. Regeneration of curl-leaf mountain mahogany occurs through seed. If stand-destroying disturbances occur, distance to a seed source can play a significant role in how long reestablishment takes. Resistance at a particular Rocky Hills site can be partially attributed to composition and canopy cover. Sites with more bare ground and lower vegetative cover are less prone to high-severity fires. Sites with these characteristics have the oldest stands of curl-leaf mountain mahogany (Gucker, 2006).

Community 1.2
Mountain Mahogany/Mixed Shrub - Bluebunch Wheatgrass Community

Figure 12. Site ID: 2021ID7031223

Figure 13. Plot of canopy cover by functional group for Rocky Hills site: 2021ID7031223

Community 1.2 is similar to Community 1.1 in that the overstory is dominated by curl-leaf mountain mahogany in the overstory and bluebunch wheatgrass in the understory. The primary difference is a decrease in curl-leaf mountain mahogany canopy cover that allows for other shrub species to occupy a greater portion of the overstory canopy. These can include big sagebrush species such as mountain big sagebrush (Artemisia tridentata spp. Vasayana), or Wyoming big sagebrush (Artemisia tridentata ssp. Wyomingensis). Other shrub species that are tolerant of calcareous soils such as black sagebrush and little sagebrush can also be present in greater quantities. Yellow rabbitbrush and spineless horsebrush (Tetradymia canescens) can also be present. Production for this community ranges from 395 to 885 pounds per acre, averaging 645 pounds per acre.

Resilience management. This community has low to moderate resilience. Although very resistant to drought and frequent or high-severity fires, this community has difficulty recovering when much of the overstory is eliminated. Regeneration of curl-leaf mountain mahogany occurs through seed. If stand-destroying disturbances occur, distance to a seed source can play a significant role in how long reestablishment takes. Resistance at a particular Rocky Hills site can be partially attributed to composition and canopy cover. Sites with more bare ground and lower vegetative cover are less prone to high-severity fires. Sites with these characteristics have the oldest stands of curl-leaf mountain mahogany (Gucker, 2006).

Community 1.3
Wooded Mountain Mahogany/Bluebunch Wheatgrass Community

Figure 15. Site ID: 2020ID7032238

Community 1.3 is dominated by curl-leaf mountain mahogany in the shrub overstory and bluebunch wheatgrass in the shrub understory. Unlike Communities 1.1 and 1.2, Community 1.3 is found at or near the transition to a timber-dominated canopy. This community will have Douglas-fir (Pseudotsuga menziesii), Rocky Mountain juniper (Juniperus scopularum), limber pine (Pinus flexus) or a combination of the three at relatively low densities in the overstory canopy. Limber pine and Rocky Mountain juniper are more prominent on sites when soils have a higher volume of calcium carbonates or are highly calcareous. Bluebunch wheatgrass remains the primary understory. Other species with lesser canopy cover include Indian ricegrass (Achnatherum hymenoides), Sandberg bluegrass (Poa secunda), and needleleaf sedge (Carex duriuscula). Other shrub species, in addition to curl-leaf mountain mahogany, include mountain big sagebrush, yellow rabbitbrush, and little sagebrush. Production in this community ranges from 500-850 pounds per acre, averaging 625 pounds per acre.

Resilience management. This community has low to moderate resilience. The introduction of Douglas-fir, Rocky Mountain juniper, and limber pine into the overstory increases the frequency and potential severity of fire. Additionally, because this community exists near transitions to timber-dominated overstory, this increases the likelihood of encroachment and possible transition to a forested ecological site. Curl-leaf mountain mahogany is susceptible to stand-destroying fires at relatively infrequent fire return intervals. Douglas-fir has a much more frequent fire return interval of seven to 20 years (Steinberg, 2002). As encroachment occurs, curl-leaf mountain mahogany is exposed to different fire regimes than those that occur within the natural range of variability.

Pathway P1-2
Community 1.1 to 1.2

Curl Leaf Mountain Mahogany/Bluebunch Wheatgrass Community

Mountain Mahogany/Mixed Shrub - Bluebunch Wheatgrass Community

The primary driver for community 1.2 is localized abiotic conditions involving highly calcareous soils. These abiotic conditions are found on Rocky Hills 15 to 19 Inch Precipitation Zone ecological sites with a higher volume of calcium carbonates within the rooting depth of the soil profile. Black and little sagebrush are well adapted to conditions where soils are highly calcareous (Tilley & St. John, 2012). Black and little sagebrush replace other shrubs and grasses in the canopy that would be present in Community 1.1.

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 P1-3
Community 1.1 to 1.3

Curl Leaf Mountain Mahogany/Bluebunch Wheatgrass Community

Wooded Mountain Mahogany/Bluebunch Wheatgrass Community

Shifts to community 1.3 are a combination of localized abiotic conditions and altered disturbance regimes. These communities occur at or near transition zones with timber-dominated areas. Without the proximity to a source, seed dispersion is less likely and Douglas-fir, Rocky Mountain juniper, and limber pine are less likely to establish. Historic-low severity fire at frequent fire return intervals limits the expansion of tree species into the Rocky Hills 10 - 14 Inch Precipitation Zone ecological site. However, suppression of fire or lack of fuels to carry fire can aid in the expansion of these forest species.

Context dependence. In addition to local abiotic conditions, fire at frequent and low severity (or lack thereof) can influence how Douglas-fir, Rocky Mountain juniper, or limber pine can establish and expand their respective range.

Pathway P2-3
Community 1.2 to 1.3

Mountain Mahogany/Mixed Shrub - Bluebunch Wheatgrass Community

Wooded Mountain Mahogany/Bluebunch Wheatgrass Community

Shifts to community 1.3 are a combination of localized abiotic conditions and altered disturbance regimes. These communities occur at or near transition zones with timber-dominated areas. Without the proximity, seed dispersion is less likely and Douglas-fir, Rocky Mountain juniper, and limber pine are less likely to establish. Historic low-severity fire at frequent fire return intervals limits the expansion of tree species into this ecological site. However, suppression of fire or lack of fuels to carry fire can aid in the expansion of these forest species.

Context dependence. In addition to local abiotic conditions, fire at frequent and low severity (or lack thereof) can influence how Douglas fir, Rocky Mountain juniper, or limber pine can establish and expand their respective range.

Pathway P3-1
Community 1.3 to 1.1

Wooded Mountain Mahogany/Bluebunch Wheatgrass Community

Curl Leaf Mountain Mahogany/Bluebunch Wheatgrass Community

Shifts to community 1.3 are a combination of localized abiotic conditions and altered disturbance regimes. These communities occur at or near transition zones with timber-dominated areas. Without the proximity to a source, seed dispersion is less likely and Douglas-fir, Rocky Mountain juniper, and limber pine are less likely to establish. Historic-low severity fire at frequent fire return intervals limits the expansion of tree species into the Rocky Hills 10 - 14 Inch Precipitation Zone ecological site. However, suppression of fire or lack of fuels to carry fire can aid in the expansion of these forest species.

Context dependence. In addition to local abiotic conditions, fire at frequent and low severity (or lack thereof) can influence how Douglas-fir, Rocky Mountain juniper, or limber pine can establish and expand their respective range.

State 2
Disturbed State

This community shifts from the shrub-dominated communities of the Reference State to a community dominated by native bunchgrass and disturbance-tolerant species. The grass species tend to be similar to that of the reference communities and include bluebunch wheatgrass, Sandberg bluegrass, and Indian ricegrass. The overstory shrub community, if present, is yellow rabbitbrush and to a lesser extent, threetip sagebrush. Production for this community is no longer weighted toward the shrub functional group, but shifts towards grasses and forbs. Production values remain relatively high, ranging from 500 to 900 pounds per acre, averaging 650 pounds per acre.

Characteristics and indicators. The Disturbed state in the Rocky Hills ecological site results from any disturbance that removes the overstory vegetation. The primary disturbance for this ecological site that results in the removal of overstory shrubs is frequent or severe fire. The dominant overstory species found in the Reference state such as curl-leaf mountain mahogany, black sagebrush, low sagebrush, and mountain big sagebrush experience high rates of mortality during severe fire events. In the immediate years following the event, canopy cover increases for early seral and disturbance-tolerant species such as yellow rabbitbrush (Chrysothamnus viscidiflorus), three-tip sagebrush (Artemisia tripartita), and the common bunchgrass species found in most communities of the Reference state. Historic fire return intervals for curl-leaf mountain mahogany stands in the Salmon River area ranged between 13 to 22 years. Because of grazing and fire exclusion, the time between fire events has increased significantly. This has resulted in fewer, but more severe stand-destroying fire events (Gucker, 2006).

Resilience management. Once in the Disturbed state, resilience is moderately high. The species present are disturbance tolerant or even perpetuated by frequent or continued disturbance events. Resilience is lost, however, by the opportunity for invasive species establishment. Openings in the canopy caused by a disturbance can allow for the recruitment of invasive species if native species don't readily occupy those spaces.

Community 2.1
Bunchgrass Community

This community shifts from the shrub-dominated communities of the Reference State to a community dominated by native bunchgrass and disturbance-tolerant species. The grass species tend to be similar to that of the reference communities and include bluebunch wheatgrass, Sandberg bluegrass, and Indian ricegrass. The overstory shrub community, if present, is yellow rabbitbrush and to a lesser extent, threetip sagebrush. Production for this community is no longer weighted toward the shrub functional group, but shifts towards grasses and forbs. Production values remain relatively high, ranging from 350 to 800 pounds per acre, averaging 600 pounds per acre.

Resilience management. This community is moderately resilient. Many of the bunchgrasses present are tolerant of continued low to moderate-severity disturbances. Bluebunch wheatgrass is able to survive all but the most severe fire disturbances because of its protected root system (Zlatnick, 1999). Sandberg bluegrass is also tolerant of disturbance and able to quickly recover to pre-disturbance canopy cover. Both of the primary shrubs that can be present in this community (yellow rabbitbrush and threetip sagebrush) are disturbance tolerant and can be perpetuated by a frequent disturbance regime.

State 3
Invaded State

The Invaded State is represented by a shift from native grasses and forbs in the understory to an understory dominated by invasive species. Transition to this state occurs after a severe disturbance that creates openings in the canopy for invasive species to establish. The primary invasive species that becomes dominant in the Invaded State is cheatgrass (Bromus tectorum). This state is especially prevalent on steep, rocky slopes where colluvial movement is active. As the soil is disturbed through movement of material downhill, ideal conditions are presented for cheatgrass recruitment. Once established and a seed source is readily available, cheatgrass is well adapted to increasing its coverage area.

Characteristics and indicators. This state is indicated by any single invasive species occupying five percent or more of the canopy, or a group of invasive species occupying 10 percent of the canopy collectively.

Resilience management. This state exhibits low resilience due to the establishment of invasive and non-native species. Once established, non-native vegetation tends to increase in canopy cover and can often be promoted by further disturbances.

Community 3.1
Invaded Shrub and Grass

This community may resemble the vegetative composition of Communities 1.1 and 1.2 within the Reference state of the ecological site; however, will have a canopy cover of five percent or greater for a single invasive species, or 10 percent or greater for all invasive species on site. Production can be high, however may not occur in desirable species. The production range for this community is 450 to 900 pounds per acre, averaging 600 pounds per acre.

Resilience management. This community is perpetuated by continued, frequent disturbances. The invasive species that occupy the site thrive when disturbance regimes shift outside the historic range of variability.

Community 3.2
Invaded Wooded Shrub and Grass

This community may resemble the vegetative composition of Community 1.3 within the Reference state of the ecological site; however, will have a canopy cover of five percent or greater for a single invasive species, or 10 percent or greater for all invasive species on site. Production can be high, however may not occur in desirable species. The production range for this community is 350 to 750 pounds per acre, averaging 500 pounds per acre.

Resilience management. This community is perpetuated by continued, frequent disturbances. The invasive species that occupy the site thrive when disturbance regimes shift outside the historic range of variability.

Pathway P1-2
Community 3.1 to 3.2

Invaded Shrub and Grass

Invaded Wooded Shrub and Grass

Shifts to community 3.2 are a combination of localized abiotic conditions and altered disturbance regimes. These communities occur at or near transition zones with timber-dominated areas. Without the close proximity, seed dispersion is less likely and Douglas-fir, Rocky Mountain juniper, and limber pine are less likely to establish. Historic low-severity fire at frequent fire return intervals limits the expansion of tree species into this ecological site. However, suppression of fire or lack of fuels to carry fire can aid in the expansion of these forest species.

Context dependence. In addition to local abiotic conditions, fire at frequent and low severity (or lack thereof) can influence how Douglas fir, Rocky Mountain juniper, or limber pine can establish and expand their respective range.

Transition T1-2
State 1 to 2

The transition from the Reference state to the Disturbed state is a mechanism of frequent or severe disturbances that remove the overstory shrubs on a given site. The most common disturbance that results in the loss of the shrub overstory is high-intensity fire. Historic fire return intervals for curl leaf mountain mahogany stands were relatively frequent (13 to 22 years) and events tended to be lower severity. Since 1900, fire exclusion has decreased fire return intervals and increased the likelihood of less frequent, more severe fire events that are often stand-destroying (Gucker, 2006).

Constraints to recovery. Constraints to recovery include: Frequent disturbances before recovery has completed; Prolonged periods of drought that diminish regeneration of desired species; Loss of nutrient-rich topsoil due to increased erosion; Establishment of invasive species; Distance from a seed source.

Context dependence. The primary factor driving the likelihood of restoration success is post-disturbance weather patterns. Prolonged periods 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 Reference state species (Steinberg, 2002 and Fryer, 2009).

Transition T1-3
State 1 to 3

Reference State

Invaded State

The transition from the Reference state to the Invaded state is result of disturbances that create opportunities for invasive species establishment. One of the primary disturbances resulting in invasion on this site is colluvial disturbances resulting from steep slopes. Soil movement downslope that disturbs the surface creates ideal conditions for the establishment of invasive species, one of the most prominent species being cheatgrass. Once locally established, cheatgrass is able to further spread across a site.

Constraints to recovery. Constraints to recovery include: The establishment speed of invasive species; Prolonged periods of drought that diminish regeneration of desired species; Loss of nutrient-rich topsoil due to increased erosion; Continued establishment and spread of invasive species.

Context dependence. Restoration success is dependent on invasive species composition and level of establishment. Removal of cheatgrass once significant establishment occurs can be resource intensive with low success rates.

Restoration pathway R2-1
State 2 to 1

Restoration from the Disturbed state to the Reference state is a mechanism of time without stand-destroying disturbance. Once the shrub overstory has been removed, replacement seedlings will need to reach maturity without any further disturbances.

Context dependence. The time frame for restoration is highly dependent on variations in localized weather patterns. Prolonged periods of drought can dramatically increase the time required to return to the Reference state, whereas periods of above-normal precipitation can decrease that time frame. Distance from a seed source of Reference state Plants can impact restoration timeframes in the absence of seeding or planting.

Transition T2-3
State 2 to 3

The transition from the Disturbed state to the Invaded state results when a disturbance removes native vegetation cover and is replaced by non-native or invasive species. If native vegetation is not able to repopulate a site after a disturbance occurs, opportunities exist for the recruitment of invasive species in their absence. The most common invasive species to cause this transition at the Rocky Hills ecological site is cheatgrass.

Constraints to recovery. Constraints to recovery include: Grazing following a disturbance; Prolonged periods of drought that diminish regeneration of desired species; Loss of nutrient-rich topsoil due to increased erosion; Establishment of invasive species.

Context dependence. Restoration efforts can be greatly influenced by precipitation patterns. Successful regeneration of Reference state understory species is highly dependent on moisture received post-restoration efforts. Rates of successful establishment of bluebunch wheatgrass and Sandberg bluegrass increase when available moisture is high during critical regeneration periods (Zlatnik, 1999 & Howard, 1997).

Restoration pathway R3-1
State 3 to 1

Invaded State

Reference State

The transition from the Disturbed state to the Invaded state results when a disturbance removes native vegetation cover and is replaced by non-native or invasive species. If native vegetation is not able to repopulate a site after a disturbance occurs, opportunities exist for the recruitment of invasive species in their absence. The most common invasive species to cause this transition at the Rocky Hills ecological site is cheatgrass.

Context dependence. Constraints to recovery include: Grazing following a disturbance; Prolonged periods of drought that diminish regeneration of desired species; Loss of nutrient-rich topsoil due to increased erosion; Establishment of invasive species.