Desert Flat (Shadscale)
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
- Transition T2b More details
- Transition T2c More details
- Restoration pathway R3a More details
- Transition T3a More details
- Transition T3b More details
- Transition T3c More details
- Restoration pathway R4a More details
- Transition T4a More details
- Restoration pathway R5a 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 includes the plant communities best adapted to the unique combinations and factors associated with this ecological site prior to Euro-American settlement. Thus, the plant communities of the Reference State are believed to be non-existent or rare. The Desert Flat ecological site is driven primarily by climatic changes ranging from multi-year drought to years when precipitation levels are high. In response, the vegetation vacillates between a community dominated by shadscale saltbush (Atriplex confertifolia) to one dominated by mixed herbs. Historically, fire was not part of this system (West 1983, Brooks and Chambers 2011). The primary limiting factors of this site are the limited water availability (8-10” precipitation zone) and presence of a natric horizon. The natric horizon contributes to increased clay content, higher sodium and/or magnesium levels, alkalinity, and pH (USDA-NRCS 2010). Infiltration rates can be slow and potential water loss through evaporation relatively high compared to other coarser-textured soils (i.e. “inverse texture principle,” Noy-Meir 1973). Furthermore, as the soil dries and temperatures increase, the natric horizon can become very hard, further limiting the availability of soil water to plants, ultimately making this ecological site more vulnerable and less resilient to disturbance than other non-restrictive shadscale-dominated sites.
Submodel
Description
State 2 is a description of the ecological site following Euro-American settlement, and the subsequent introduction of several non-native plants and animals. Climate change may also cause State 1 to shift into State 2, regardless of the land management practice. The plant community is very similar to State 1 with the exception that several introduced species including cheatgrass (Bromus tectorum), Russian thistle (Salsola spp.), halogeton (Halogeton glomeratus), tall tumblemustard (Sisymbrium altissimum), redstem stork's bill (Erodium cicutarium), and curveseed butterwort (Ceratocephala testiculata) are likely to be present. Once established, there is no practical method to effectively remove these plants from the site. Additionally, microphytic crusts are likely to be diminished or absent depending on disturbance history.
Although shadscale-dominated sites are typically characterized by lower precipitation, in some years the amount and timing of precipitation fluctuates. When precipitation is higher than normal, these sparsely vegetated sites are less effective at utilizing the increased resource (i.e. available water), and therefore are considered more susceptible to invasive species (i.e. fluctuating resource hypothesis) (Davis et al. 2000, Brooks and Chambers 2011). In some areas, invasive grasses have increased enough to fill interspaces between shrubs allowing the site to carry fire, an extremely unusual event in historic salt desert shrublands (West 1994, Brooks and Chambers 2011).
Shadscale is used for forage by all classes of livestock, as well as mule deer and pronghorn antelope. Historically, lower desert communities including the Desert Flats were used for grazing of sheep during winter months. Prior to the Taylor Grazing Act of 1934, many of these areas were overgrazed and depending on the intensity, type of livestock, and season of use, the community was set onto various trajectories (Kitchen and Hall 1996).
Submodel
States 1, 5 and 2 (additional transitions)
2.1. Shadscale Saltbush
2.5. Increasing non-native annuals/Diminished shrubs
2.2. Mixed herbs
Description
The Seeded Range State exists where managers decided to re-seed in order to address management concerns such as the need to increase forage production, control soil erosion, and/or suppress wildfire. Re-vegetation efforts often utilize non-native perennial herbs that mimic the structure and function of but are more competitive than native species (Brooks and Chambers 2011, Davies et al. 2010, DiTomaso and Smith 2012, Hirsch and Monaco 2011, Newhall et al. 2004). Therefore, these areas are often dominated with non-native perennial grasses (e.g. crested wheatgrass). Forage kochia is an introduced semi-shrub that is commonly used in revegetation and fire suppression (Monaco et al. 2003). In some cases, monocultures of the seeded species were created. However, more recent seedings have included a broader suite of species (and cultivars) to increase germination rate and assist succession and recovery of the native shadscale community (State 2). Depending on grazing levels, drought, and seed source availability, shadscale and a mix of other native species will re-establish over time. State 3 can be maintained when livestock grazing is compatible with current site productivity, but continued heavy livestock grazing will negatively impact resiliency. Non-native annuals such as cheatgrass and tall tumblemustard are common invaders in these areas.
Submodel
Description
The Invasive Annuals State is a degraded condition as a result of long-term heavy grazing and invasion by annuals. Halogeton and/or cheatgrass are typically dominant.
Submodel
Description
The Eroded State is a highly degraded condition as a result of extreme wildfire and very powerful, persistent winds removing most if not all vegetation. In some areas, multiple inches of soil may be lost, while deposition and dunning may occur in other areas.
Submodel
Mechanism
The introduction of exotic flora and fauna, possible extinctions of native flora or fauna, along with climate change, will cause State 1 to transition to State 2. Reversal of these changes back to State 1 is impracticable. These soils are easily disturbed by trampling. Compacted areas are more susceptible to wind or water erosion. Perennial vegetation decreases while bare ground increases leading to further runoff and soil loss.
Mechanism
Over the years, land managers have seeded rangelands for a variety of reasons. Historical tilling and removal of shadscale through chemical or mechanical means, followed by seeding of non-native perennial grasses such as crested wheatgrass (Agropyron cristatum) was done to increase forage production. In areas where annuals have invaded and fire is of concern, drilling and re-seeding with forage kochia (Bassia prostrata) to create fuel-breaks (i.e. “greenstripping”) has also been employed (Monaco et al. 2003).
Mechanism
Heavy continuous season- (or year-) long grazing will worsen the fragile conditions of Community Phase 2.5 (Increasing non-native annuals/ Diminished shrubs) and create positive feedbacks to further degradation. Other Community Phases of State 2 (i.e. 2.1, 2.2, 2.3, and 2.4) could possibly sustain longer periods with heavy grazing, but this would eventually lead to Community Phase 2.5, and ultimately pass an ecological threshold into State 4. Annual species, particularly halogeton and cheatgrass, benefit from continued disturbance. Soils will become more compacted and susceptible to erosion.
Mechanism
The unusual event of extreme wildfire and intense winds will move State 2 to a completely unvegetated and eroded state. If there is no plant cover and high winds continue, resident soils will be displaced and upwind soils may move in creating dune environments. Seed establishment is not possible under these conditions creating a positive feedback that is difficult to reverse.
Mechanism
If a period of time passes without fire (or other significant disturbance), grazing practices are compatible with productivity, and there is evidence of re-establishment of native shrubs and perennial grasses, it is possible that the Seeded Range State can be restored to the former Shadscale Saltbush/ Introduced Non-native Herbs State.
Mechanism
If the Seeded Range State receives heavy continuous season- (or year-) long grazing, this will reduce the seeded and/or re-establishing perennial species (herbs and shrubs) and continue to disturb the soils, potentially creating a positive feedback where annual species, such as halogeton and cheatgrass, are the few species able to persist. Soils will be more compacted and susceptible to erosion.
Mechanism
Depending on the intensity, frequency, and availability of exotic annuals, wildfire may reduce the seeded and/or re-establishing perennial species (herbs and shrubs), and push the community into one dominated by invasive annuals.
Mechanism
The unusual event of extreme wildfire and intense winds will move the Seeded Range State to a completely unvegetated and eroded state. If vegetation cover is low and winds are high, resident soils may continue to erode and upwind soils may move to create dune environments. Seed establishment is not possible under these conditions thus creating a positive feedback that is difficult to reverse.
Mechanism
Depending on the degree plant-soil feedbacks have changed (see: Community Phase 4.1), the potential to transition the Invasive Annuals State to a seeded range state may be practicable if the species selected for seeding are known to tolerate the “invader-cultured soil” (Grant and Paschke 2012, Newhall et al. 2004), provided a favorable climate and appropriate grazing practices are imposed. “Greenstripping” with forage kochia to facilitate the establishment of persistent vegetation and fire-breaks has been successfully employed as well (Monaco et al. 2003). Regardless of the land treatment, the landscape setting including the juxtaposition of particular landforms and soil properties should be considered carefully. Depending on the spatial extent and connectivity of the disturbance, land treatments can have variable impacts on aeolian sediment fluxes (i.e. wind erosion), particularly in areas with persistent high winds and fragile soils (Miller et al. 2012). For example, upwind soil and vegetation conditions are important factors when predicting and mitigating potential downwind erosion dynamics (Miller et al. 2012).
Mechanism
The unusual event of extreme wildfire and intense winds will move the Invasive Annuals State to a completely unvegetated and eroded state. If there is no vegetation cover and winds are high, resident soils will continue to erode, or in some cases other soils can be blown in creating dune environments. Seed establishment is not possible under these conditions thus creating a positive feedback that is difficult to reverse.
Mechanism
It may be possible to transition the Eroded State to a seeded range state, provided the seeded species are capable of surviving in these extremely harsh conditions (Newhall et al. 2004), the area receives enough precipitation, and careful consideration is made to the landscape setting (i.e. juxtaposition of certain landforms and soil properties) (Miller et al. 2012). The spatial extent and connectivity of land treatments, particularly in areas with high winds and fragile soils, can directly influence aeolian sediment flux through saltation. Upwind soil and vegetation conditions are important factors when predicting and mitigating potential downwind erosion dynamics (Miller et al. 2012). Arranging drill rows perpendicularly to prevailing winds, installing fences to catch sediments, and limiting grazing disturbances would be important mitigation measures to reduce erosion. Herbicides should be used with caution, as the cover of exotic annual plants can provide protection for perennial seedlings as they re-establish.
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