Ecological dynamics
It is impossible to determine in any quantitative detail the Reference Plant Community for this ecological site because of the lack of direct historical documentation preceding all human influence. In some areas, the earliest reports of dominant plants include the cadastral survey conducted by the General Land Office, which began in the late 19th century for this area (Galatowitsch 1990). However, up to the 1870s the Shoshone Indians, prevalent in northern Utah and neighboring states, grazed horses and set fires to alter the vegetation for their needs (Parson 1996). In the 1860s, Europeans brought cattle and horses to the area, grazing large numbers of them on unfenced parcels year-long (Parson 1996). Itinerant and local sheep flocks followed, largely replacing cattle as the browse component increased.
Below is a State and Transition Model diagram to illustrate the “phases” (common plant communities), and “states” (aggregations of those plant communities) that can occur on the site. Differences between phases and states depend primarily upon observations of a range of disturbance histories in areas where this ESD is represented. These situations include grazing gradients to water sources, fence-line contrasts, patches with differing dates of fire, herbicide treatment, tillage, etc. Reference State 1 illustrates the common plant communities that probably existed immediately prior to European settlement.
The major successional pathways within states, (“community pathways”) are indicated by arrows between phases. “Transitions” are indicated by arrows between states. The drivers of these changes are indicated in codes decipherable by referring to the legend at the bottom of the page and by reading the detailed narratives that follow the diagram. The transition between Reference State 1 and State 2 is considered irreversible because of the naturalization of exotic species of both flora and fauna, possible extinction of native species, and climate change. There may have also been accelerated soil erosion.
When available, monitoring data (of various types) were employed to validate more subjective inferences made in this diagram. See the complete files in the office of the State Range Conservationist for more details.
The plant communities shown in this State and Transition Model may not represent every possibility, but are probably the most prevalent and recurring plant communities. As more monitoring data are collected, some phases or states may be revised, removed, and new ones may be added. None of these plant communities should necessarily be thought of as “Desired Plant Communities.” According to the USDA NRCS National Range & Pasture Handbook (USDA-NRCS 2003), Desired Plant Communities (DPC’s) will be determined by the decision-makers and will meet minimum quality criteria established by the NRCS. The main purpose for including descriptions of a plant community is to capture the current knowledge at the time of this revision.
State 1
Reference State
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.
Community 1.1
Indian ricegrass & other perennial grasses/ Greasewood
Community Phase 1.1: Indian ricegrass & other perennial grasses/ Greasewood
This plant community (1.1) would have been characterized by a co-dominance of Indian ricegrass and greasewood. Other perennial grasses such as Western wheatgrass and basin wildrye would have been common as well.
State 2
Indian Ricegrass/ Greasewood/ Introduced Non-natives State
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.
Community 2.1
Indian Ricegrass/ Greasewood/ Introduced Non-natives State
Community Phase 2.1: Indian ricegrass & other perennial grasses/ Greasewood
This plant community (2.1) is characterized by a co-dominance of Indian ricegrass and greasewood. Other perennial grasses such as Western wheatgrass and basin wildrye are also common.
Pathway CP 2.1A
Community 2.1 to 2.2
Community Pathway 2.1a
Heavy continuous season-long grazing by livestock will reduce the perennial grass component, shifting the community towards greasewood dominance and expansion of introduced exotics such as burningbush (Kochia scoparia), prickly Russian thistle (Salsola tragus) and saltlover (Halogeton glomeratus).
Pathway CP 2.2A
Community 2.2 to 2.1
Community Pathway 2.2a
A release from livestock grazing pressure will allow the perennial grasses to re-establish and bring the plant community back to a co-dominance of Indian ricegrass & greasewood (2.1).
State 3
Greasewood/ Gardner’s Saltbush State
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.
Community 3.1
Greasewood/ Gardner’s Saltbush State
Community Phase 3.1: Greasewood/Gardner’s saltbush
This plant community (3.1) is characterized by a co-dominance of greasewood and Gardner’s saltbush.
State 4
Wyoming Big Sagebrush/ Greasewood State
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.
Community 4.1
Wyoming Big Sagebrush/ Greasewood State
Community Phase 4.1: Wyoming big sagebrush/ greasewood
This plant community (4.1) is characterized by a co-dominance of Wyoming big sagebrush and greasewood.
Transition T1A
State 1 to 2
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.
Transition T2A
State 2 to 3
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.
Transition T2B
State 2 to 4
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.
