Semi-desert Saline Well-Drained Terraces (Indian ricegrass/ Greasewood)
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
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Transition T1A
Introduction of exotic species, both plants and animals, and possible extinctions of native flora and fauna, along with climate change
More details -
Transition T2A
Heavy continuous season-long grazing and partial erosional loss of the upper part of the soil profile
More details -
Transition T2B
Extreme down-cutting and channelization of arroyos
More details -
No transition or restoration pathway between the selected states has been described
Target ecosystem state
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Description
The Reference State is a description of this ecological site just prior to Euro-American settlement but long after the arrival of Native Americans. The description of the Reference State was determined by NRCS Soil Survey Type Site Location information and familiarity with rangeland relict areas where they exist. The plant community (1.1) within the Reference State would have been co-dominated by Indian ricegrass (Achnatherum hymenoides) and greasewood (Sarcobatus vermiculatus). Other perennial grasses such as Western wheatgrass (Pascopyrum smithii) and basin wildrye (Leymus cinereus) would also have been common. A more complete list of species by lifeform for the Reference State is available in the accompanying tables in the “Plant Community Composition by Weight and Percentage” section of this document.
Submodel
Description
State 2 is very similar to State 1 in form and function, with the exception of the presence of non-native plants and animals, possible extinctions of native species, and a different climate.
State 2 is a description of the ecological site shortly following Euro-American settlement. This state can be regarded as the current potential. The least modified plant community (2.1) is co-dominated by Indian ricegrass and greasewood. Other perennial grasses such as Western wheatgrass and basin wildrye may also be common. The relative cover of the perennial grasses may be reduced with heavy grazing by livestock (2.1a) resulting in a greasewood-dominated phase (2.2). Provided there is some remaining perennial grass seed source and compaction from livestock has not occurred, these sites may return to a co-dominant plant community of native perennial grasses and greasewood (2.1) after the pressure from livestock has been minimized (2.2a).
With the proper balance between shrub and perennial grass cover, the site will be resilient to moderate to light grazing effects. The resiliency of this state is maintained by ground cover, provided by both grasses and leaf litter, which helps maintain soil stability and retention of water at the site. Reduction of perennial grass cover puts this state at risk for further degradation due to lack of soil stabilization and reduction soil moisture retention.
Protection from heavy grazing may prevent loss of the understory component and soil compaction, both of which make the site more susceptible to down-cutting of gullies. Severe channelization, or where erosional movement of fines covering sands and gravels in the soil subsurface allow for better drainage, could lead to a permanent lowering of the water table. This change in hydrologic regime will result in decreasing the salinity of surface soils, thus allowing the invasion of Wyoming big sagebrush (Artemisia tridentata spp. wyomingensis) into what was otherwise a chenopod-dominated (greasewood) shrubland rooted in saltier surface fines.
Submodel
Description
Greasewood and Gardner’s saltbush (Atriplex gardneri) are found on sites where heavy continuous season-long grazing and some soil erosion have occurred. Site resiliency (resistance to change) is maintained by the absence of perennial grass seed source and partial soil surface loss, preventing the re-establishment of the understory component.
Submodel
Description
Where extreme down-cutting and channelization of these saline terraces has taken place, the water table will drop allowing glycophytic (not salinity tolerant) species such as Wyoming big sagebrush to move in and occupy the site in addition to the deeply tap-rooted greasewood. The resiliency (resistance to change) of this state is maintained by a lower water table and the associated change in soil chemistry (reduction is soil surface salts), which allows the establishment of Wyoming big sagebrush. The lack of native perennial grasses is maintained by the lack or depletion of seed source for those species.
Submodel
Mechanism
Transition T1a: from State 1 to State 2 (Reference State to Indian Ricegrass/ Greasewood/ Introduced Non-natives State)
The simultaneous introduction of exotic species, both plants and animals, and possible extinctions of native flora and fauna, along with climate change, has caused State 1 to transition to State 2. Reversal of such historic changes (i.e. a return pathway) back to State 1 is not practical.
Mechanism
Transition T2a: from State 2 to State 3 (Indian Ricegrass/ Greasewood/ Introduced Non-natives State to Greasewood/Gardner’s Saltbush State)
The Indian Ricegrass/ Greasewood/ Introduced Non-natives State will transition to the Greasewood/ Gardner’s Saltbush State following heavy continuous season-long grazing and partial erosional loss of the upper part of the soil profile. The approach to this transition is indicated by a loss of perennial understory grass, an increase in the shrub component relative to grasses, in increase in bare soil, and/or soil loss. Sustained heavy grazing, especially during the growth season for grasses, will trigger the transition. Restoration (return to State 2) is impracticable due to the lack of native perennial grass seed source and partial soil loss.
Mechanism
Transition T2b: from State 2 to State 4 (Indian Ricegrass/ Greasewood/ Introduced Non-natives State to Wyoming Big Sagebrush/ Greasewood State)
The Indian Ricegrass/ Greasewood/ Introduced Non-natives State will transition to the Wyoming Big Sagebrush/ Greasewood State following extreme down-cutting and channelization of arroyos. The approach to this transition is indicated by a loss of the perennial grass understory and by soil compaction (evidenced by the presence of terracettes and mounded micro-relief around shrubs, with depressions between shrubs). The combined effect of sustained heavy grazing and soil compaction over time, coupled with a sudden flash flood event (or a sudden flash flood event alone), will trigger the transition. Restoration (return to State 2) is impracticable due to severe soil erosion and changes in soil chemistry, and due to the lack of native perennial grass seed source.
Model keys
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