Natural Resources
Conservation Service
Semidesert Sandy Loam (Blackbrush)
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
- Transition T1a More details
- Transition T2a 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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State 1
Reference State
Reference State
Description
This Reference State was determined by the study of rangeland relic areas and areas protected from excessive disturbance and influences such as improper livestock grazing and high impact recreation. Literature reviews, historical accounts and observations of trends in plant community dynamics under a variety of sites has also been considered. Community phases, community pathways, other states, transitions, and thresholds, have been determined through similar studies and experience.
The reference state represents the plant communities and ecological dynamics of the semidesert sandy loam, blackbrush site. This state includes the biotic communities that become established on the ecological site if all successional sequences are completed under the natural disturbance regime. The reference state is generally dominated by blackbrush, however depending on disturbance history, native grasses, forbs, or other shrubs may dominate the site. Utah juniper can naturally invade on the moderately deep soil components when the site is in close proximity to a juniper dominated ecological site. Due to the ability of Utah juniper to out compete other understory species on this site, blowout areas are common where this species occurs. Primary disturbance mechanisms include infrequent fire, climate fluctuations, and native herbivore grazing. The timing of these natural disturbances dictates the ecological dynamics that can occur. The reference state is self sustaining and resistant to change due to high resistance to natural disturbances and high resilience following natural disturbances. When these natural disturbances occur, the rate of recovery is quite variable depending on disturbance intensity. The reference state will naturally fluctuate between community phases 1.1 and 1.2, however once these sites are disturbed by fire, a return to these community phases may not be possible.
Reference State: Plant communities influenced by infrequent fire, native herbivore grazing, and climate fluctuations.
Indicators: A community dominated by blackbrush where native perennial grasses and forbs may also be present.
Feedbacks: Natural fluctuations in climate that allow for a self sustaining blackbrush and native grass community. Stand replacing fires which may or may not fully recover to a blackbrush dominated community. Improper livestock grazing, more frequent fire, or other disturbance that may allow for the establishment of non-native species.
At-risk Community Phase: All communities are at risk when native plants are stressed and nutrients become available for invasive plants to establish.
Trigger: The establishment of non-native invasive plant species.
Submodel
Communities 1, 5 and 2 (additional pathways)
1.1. Blackbrush Shrubland
1.5. Native Shrubland
1.2. Blackbrush Shrubland with Grass
State 2
Current Potential State
Current Potential State
Description
The current potential state is similar to the reference state except that non-native, invasive species are now present in all community phases. This state is generally dominated by blackbrush, however, depending on disturbance history, native grasses, forbs, and/or other shrubs may dominate the site. Utah juniper can invade this state on the moderately deep soil components when the site is in close proximity to a juniper dominated ecological site. Due to Utah junipers ability to out compete associated understory plants, blowout areas are common where this species occurs. Primary disturbance mechanisms include infrequent fire, weather fluctuations, native herbivore grazing, domestic livestock grazing and surface disturbances such as road and pipeline development and off road vehicle (OHV) use. Timing of these disturbances dictates the ecological dynamics that will occur. The current potential state is still self sustaining; but is losing resistant to change due to lower resistance to disturbances and lower resilience following disturbances. When disturbances do occur, the rate of recovery is highly variable depending on severity. The current potential state will naturally fluctuate between community phases 2.1 and 2.2, however once the site is disturbed by fire or other surface disturbance, return to these community phases may not be possible.
Current Potential State: Plant communities influenced by infrequent fire, native herbivore grazing, climate fluctuations, domestic livestock grazing, and other surface disturbances.
Indicators: A community dominated by blackbrush where native perennial grasses and forbs may also be present. Non-native invasive grasses and forbs are now present.
Feedbacks: Natural fluctuations in weather that allow for self sustaining blackbrush and grass communities. Improper livestock grazing which results in a decrease of the perennial grass canopy. Stand replacing fires, or other surface disturbances, which remove blackbrush and sites may or may not fully return to a blackbrush dominated community. Frequent fire or other disturbance that may allow for the dominance of annual grasses, such as cheatgrass.
At-risk Community Phase: All communities are at risk as increased disturbance frequency allows for the dominance of annual grasses, such a cheatgrass.
Trigger: Reoccurring fire that results in a dominance of cheatgrass.
Submodel
Communities 1, 5 and 2 (additional pathways)
2.1. Blackbrush Shrubland
2.5. Shrubland
2.2. Blackbrush Shrubland with Grass
Description
This state’s ecological processes are driven by the dominance of cheatgrass, native and invasive plant species may or may not also be present. Cheatgrass dramatically affects the soil/plant/water relationships of a site. Once cheatgrass has invaded a site, the fundamental nutrient cycling processes, root pores, mycorrhizal associations, microbial species, and soil organic material change (Chapin et al. 1997; Belnap and Phillips, 2001). These alterations may eventually create ecologically impoverished sites that are very difficult to restore diverse perennial herbaceous and woody communities. The competitiveness of cheatgrass and its ability to quickly establish after a disturbance make this state extremely resistance to change and resilient after a disturbance.
Annual Grass State – Community phases maintained, in a self-sustaining manner, by frequent fire.
Indicators: A site where ecological processes are driven by cheatgrass
Feedbacks: A self sustaining disturbance regime of frequent fire.
Submodel
Mechanism
Transition from Reference State (State 1) to Current Potential State (State 2). This transition is from the native perennial warm and cool season grass understory in the reference state to a state that contains non-native species. Events include any combination of improper livestock grazing, prolonged drought, fire, surface disturbances, etc. Non-native invasive species such as cheatgrass however, has been known to invade intact perennial plant communities with little to no disturbance. Once non-natives are found in the plant community a threshold has been crossed.
Mechanism
Transition from Current Potential State (State 2) to Annual Grass State (State 3). This unlikely transition is from the current potential state into a state dominated by cheatgrass. This transition occurs as events favor the increased establishment and dominance of cheatgrass. Typically this occurs as a series of fires which lead to an increase in cheatgrass and a subsequent decrease in the fire return interval. Once cheatgrass drives the ecological dynamics of the site a threshold has been crossed. This transition may or may not occur. Cheatgrass is not known to invade the blackbrush communities in the Colorado Plateau as readily as it does in the Mohave and the Great Basin. Many times cheatgrass will be abundant 15-20 years post disturbance, but will decrease back to pre-disturbance levels 20-35 years post disturbance (Callison, 1985). Cheatgrass doesn’t seem to dominate these sites enough to cause a significant decrease in the fire return interval, which would allow cheatgrass to drive the ecological dynamics of this ecosystem.
Model keys
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