Rocky Hills 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
- Transition T1C More details
- Restoration pathway R2A More details
- Transition T2A More details
- Restoration pathway R3A More details
- Transition T3A 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 curl-leaf mountain mahogany-dominated community (1.1), which can include curl-leaf mountain mahogany, mountain big sagebrush (Artemisia tridentata ssp. vaseyana), little 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 scopulorum), and limber pine (Pinus flexilis). 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 inclusion of low elevation tree species at moderately low canopy cover. 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 and lack of fire at historic return intervals. 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. Lack of low to moderate severity fire (exceeding historic fire return intervals) can result in transition to Community 1.2 as tree species begin to increase in canopy cover.
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).
Submodel
Description
When a Rocky Hills 15-19 Inch Precipitation Zone ecological site enters the Grazing Resistant state, the primary shift occurs in the understory vegetation. Grazing pressure from livestock, native ungulates, or a combination of the two drives a shift from the cool-season bunchgrasses that are present in the Reference state towards rhizomatous wheatgrasses, short-stature bunchgrasses, and ground-covering forbs. This state is generally a result of current or historic improper grazing practices that potentially included higher stocking rates and repeated heavy grazing during the growing season.
Characteristics and indicators
In this state, total canopy cover and production values for mid to large sized bunchgrasses such as bluebunch wheatgrass will decrease. These understory grasses will be relegated to the protected areas under the sagebrush canopies where they are sheltered from grazing. As they are removed from the canopy gaps, they will be replaced with grazing-resistant short-stature bunch grasses like Sandberg bluegrass (Poa secunda) and rhizomatous wheatgrasses. Openings in the canopy gaps vacated by bunchgrasses also present opportunities for an increase in disturbance-tolerant forbs such as spiny phlox (Phlox hoodii), cushion phlox (Phlox pulvinata), vetch species (Vicia ssp.), and Indian paintbrush species (Castilleja ssp.). Opportunities for invasive annual grasses also increase as competition from native grasses is removed from the canopy gaps.
Depending on how well grazing-resistant rhizomatous and bunchgrasses occupy the gaps within the canopy, an increase in bare ground cover usually occurs. This can lead to increased erosion and decreased infiltration, decreasing available moisture. Because of this, productivity and canopy cover will be lower than at the Reference state.
Resilience management
Resilience in this state is lower than in the Reference state, primarily due to the decrease in available moisture and the opportunity for invasive species recruitment. The ability to recover from disturbance in rangeland systems is in part related to local climatic conditions. As available moisture increases and temperature decreases, resilience to disturbance increases (Chambers et al., 2014). Intensive grazing that results in chronic defoliation also promotes recruitment of invasive species, which lowers site resilience.
Submodel
Description
The Disturbed state in the Rocky Hills 15-19 Inch Precipitation Zone 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), threetip 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, time between fire events has increased significantly. This has resulted in fewer, but more severe stand destroying fire events (Gucker, 2006).
Characteristics and indicators
This state is distinguished by the lack of curl-leaf mountain mahogany and sagebrush overstory. This is accompanied by an increase in bunchgrass and other early seral grass species as well as disturbance-tolerant shrub species such as yellow rabbitbrush and threetip sagebrush. Canopy cover for mahogany and sagebrush can still be present, however, it is sparse, ranging between zero to eight percent canopy cover on a site.
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 recruitment of invasive species if native species don't readily occupy those spaces.
Submodel
Description
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.
Submodel
Mechanism
The transition from the Reference state to the Grazing Resistant state is a mechanism of intensive grazing practices that result in chronic defoliation of the understory vegetation. Over time, species like bluebunch wheatgrass are not able to recover from defoliation, and total canopy cover of that species will decrease on a site. In the absence of these species, grazing-tolerant plants such as Sandberg bluegrass will increase in canopy cover and production.
Constraints to recovery
Constraints to recovery include: Continued improper grazing techniques that result in chronic defoliation of vegetation; Prolonged periods of drought that diminish regeneration of desired species; Loss of nutrient rich top soil 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).
Mechanism
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 top soil due to increased erosion; Establishment of invasive species; Distance from seed source.
Context dependence
The primary factor driving 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; Fryer, 2009).
Mechanism
Transition from the Reference state to the Invaded state is usually a result of colluvial disturbances on steep slopes. Soil movement downslope that disturbs the surface creates ideal conditions for 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: Establishment speed of invasive species; Prolonged periods of drought that diminish regeneration of desired species; Loss of nutrient rich top soil 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 cheat grass once significant establishment occurs can be resource intensive with low success rates.
Mechanism
The primary mechanism for restoration from the Grazing Resistant state to the Reference state is rest from grazing. Reference state grasses such as bluebunch wheatgrass will not be able to re-establish while grazing pressure continues. Seeding of desired species may speed up the restoration process.
Context dependence
Time frame for restoration is highly dependent on variations in localized weather patterns. Prolonged periods of drought can dramatically increase time required to return to the Reference state, whereas periods of above normal precipitation can decrease that time frame.
Grazing practices that are infrequent and of light intensity, mimicking natural grazing patterns will not impact the restoration pathway. However, continuous early-season grazing at moderate to high intensity resulting in significant defoliation will perpetuate the Grazing Resistant state.
Mechanism
The transition from the Grazing Resistant state to the Invaded state occurs when Reference state grass species are removed through grazing which results in chronic defoliation. This leaves openings that can often be exploited by invasive species such as cheatgrass.
Constraints to recovery
Constraints to recovery include: Continued improper grazing techniques; Prolonged periods of drought that diminish regeneration of desired species; Loss of nutrient rich top soil due to increased erosion; Establishment of invasive 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.
Mechanism
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
Time frame for restoration is highly dependent on variations in localized weather patterns. Prolonged periods of drought can dramatically increase 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 representative plants from the Reference state can impact restoration timeframes in the absence of seeding or planting.
Mechanism
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 top soil 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).
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