Semi-desert Dense Clay (Low and/ or Early sagebrush/ Rhizomatous wheatgrass)
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
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Transition T1A
The simultaneous introduction of exotic species, both plants and animals, and extinctions of native flora and fauna, along with climate change
More details -
Transition T2A
Sustained heavy grazing during the growing season
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 prior to Euro-American settlement but 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 Reference State for this site would have been a sagebrush dominated semi-desert state, where low sagebrush (Artemisia arbuscula ssp. arbuscula) would have been dominant on upper slopes, especially windswept tops of slopes with shallower profiles, and early sagebrush (Artemisia arbuscula ssp. longiloba) would have been dominant on lower slopes with deeper clay soils. Minor amounts of bud sagebrush (Picrothamnus desertorum) would have been a likely companion in both circumstances. Mixtures of these three sagebrushes occurred in between. The entire ecological site was characterized by dense clay derived from alluviation of Mesozoic age rock. Soils on this site crack deeply with drought, which tends to disfavor shrubs and favor fibrous grass roots. The balance between bunchgrasses and rhizomatous grasses also would have varied with slope position and soil depth, where bunchgrasses would have been found on steeper, shallower sites, while rhizomatous grasses would have been found on deeper soils of lower slopes (Noy-Meir, 1973). 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. Herbs in this state have a later phenology. State 2 is a description of the ecological site shortly following Euro-American settlement, and is characterized by a denser sagebrush stand with a warm season herbaceous understory.
Submodel
Description
Heavy year-round grazing, mainly by sheep, resulted in a super-dominance of low or early sagebrush. The herbaceous understory was effectively nonexistent. The effective aridity of the Semi-desert Dense Clay ecological site makes it a poor prospect for management toward greater forage productivity. Furthermore, accelerated soil erosion from tillage could create problems further down the watershed. We suggest trials of small scale manipulations that are monitored closely for observation of biological responses and soil erosion.
Submodel
Mechanism
Transition T1a: from State 1 to State 2 (Reference State to Low &/or Early Sagebrush/
Rhizomatous Wheatgrass/ Introduced Herb State)
The simultaneous introduction of exotic species, both plants and animals, and extinctions of native flora and fauna, along with climate change, causes State 1 to transition to State 2, which is the current potential. Reversal of such historic changes (i.e. a return pathway) back to State 1 is not practical. Livestock grazers typically favored spring grazing, and with the diminution of the cool season grasses, the next best use of green forage occurred later in the growing season. As a result, after heavy spring livestock grazing, bunchgrasses could not compete with the rhizomatous species and shrubs.
Mechanism
Transition T2a: from State 2 to State 3 (Low &/or Early Sagebrush/ Rhizomatous Wheatgrass/ Introduced Herb State to Sagebrush Super-dominance State)
Expansion to year-around use (T2), especially with use of itinerant sheep will lead to reduction of the rhizomatous wheatgrasses and sagebrush super-dominance (State 3). The approach to this transition is indicated by a loss of perennial grass understory, an increase in shrub component relative to grasses, and soil loss. Sustained heavy grazing during the growing season will trigger the transition. A restoration pathway is impracticable due to lack of grass seed source and soil loss.
Model keys
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