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 just 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/or 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. Before Euro-American settlement, this would have been a sparsely vegetated variant of semi-desert sagebrush with about 40 percent of the forage production from grasses, 10 percent from forbs, and 50 percent from woody plants, primarily from Wyoming big sagebrush (Artemisia tridentata spp. wyomingensis). The productivity would have been relatively lower than nearby sites (e.g. R034AY2llUT Semi-desert Gravel Ecological Site) because of the Inverse Texture Principle (Noy-Meir, 1973). The major grasses would have included the caespitose form of bluebunch wheatgrass (Pseudoroegneria spicata), Western wheatgrass (Pascopyrum smithii), needle-and-thread (Hesperostipa comata), Indian ricegrass (Achnatherum hymenoides), prairie junegrass (Koeleria macrantha), and bottlebrush squirreltail (Elymus elymoides). Other associated woody species may have included yellow rabbitbrush (Chrysothamnus viscidiflorus), and winterfat (Krascheninnikovia lanata). 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. Total annual forage production would have been about 350 to 400 pounds per acre on flat to moderately sloping uplands. The fire return interval would have been on average approximately 40-50 years. The phases of this State would have depended on the time since last fire, starting with a bluebunch wheatgrass-dominated site (1.1) immediately following fire (1.3a, 1.2b), with yellow rabbitbrush becoming temporarily dominant 30 to 40 years post fire (1.2), followed by return to Wyoming Big sagebrush dominance with bunchgrass understory (1.3) 40 to 50 years post fire (1.2a).
Community 1.1
Bluebunch wheatgrass/ Scattered Wyoming big sagebrush
Community Phase 1.1: Bluebunch wheatgrass/ Scattered Wyoming big sagebrush
This plant community would have been characterized by the temporary dominance of assorted native perennial bunchgrasses, primarily the caespitose form of bluebunch wheatgrass, with scattered Wyoming big sagebrush. Dominant grasses would have included Western wheatgrass, needle-and-thread, Indian ricegrass, prairie junegrass, and bottlebrush squirreltail. This community would have existed for approximately the first decade following fire.
Community 1.2
Yellow rabbitbrush/ Wyoming big sagebrush increasing
Community Phase 1.2: Yellow rabbitbrush/ Wyoming big sagebrush increasing
This plant community would have existed approximately 30 to 40 years post wildfire, and would have had yellow rabbitbrush as the dominant species, with a slight increase in Wyoming big sagebrush.
Community 1.3
Wyoming big sagebrush dominant/ bluebunch wheatgrass & other native perennial bunchgrasses
Community Phase 1.3: Wyoming big sagebrush dominant/ bluebunch wheatgrass & other native perennial bunchgrasses
The balance between Wyoming big sagebrush and bluebunch wheatgrass would have returned following at least a 40 year period since the last wildfire. Other native perennial bunchgrasses such as Western wheatgrass, needle-and-thread, Indian ricegrass, prairie junegrass, and bottlebrush squirreltail would have also been present.
Pathway CP 1.1A
Community 1.1 to 1.2
Community Pathway 1.1a:
As time increased since the last wildfire, yellow rabbitbrush and Wyoming big sagebrush would have increased.
Pathway CP 1.2B
Community 1.2 to 1.1
Community Pathway 1.2b:
Wildfire would have reset the successional clock back to a graminoid dominated site, temporarily removing most of shrubs.
Pathway CP 1.2A
Community 1.2 to 1.3
Community Pathway 1.2a:
As length of time increased since the last wildfire, (i.e. greater than 40 years) the balance between Wyoming big sagebrush and bluebunch wheatgrass would have slowly returned.
Pathway CP 1.3A
Community 1.3 to 1.1
Community Pathway 1.3a
Wildfire would have reset the successional clock back to a graminoid dominated site, removing the majority of the sagebrush and allowing the native perennial bunchgrasses, mainly bluebunch wheatgrass, to increase and be temporarily dominant.
State 2
Wyoming Big Sagebrush/ Caespitose Bluebunch Wheatgrass/ 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 immediately following Euro-American settlement, and can be regarded as the current potential for this site. The phases of this State vary between a bluebunch wheatgrass dominated phase (2.1), to a yellow rabbitbrush/ Wyoming big sagebrush invaded phase (2.2), to a Wyoming big sagebrush with bluebunch wheatgrass understory phase (2.3), which develop according to the time since last wildfire (2.3a or 2.2b, 2.1a, 2.2a, respectively). This State is maintained by periodic wildfire, which reduces the sagebrush component, and a productive understory capable of providing a seed source for native herbaceous species. The resiliency of this state is reduced by lack of occasional wildfire and loss of native seed source. Moderate levels of growing-season livestock utilization will allow this State to maintain its resiliency, but excessive levels of growing-season livestock utilization will reduce its resiliency.
Community 2.1
Bluebunch wheatgrass/ Scattered Wyoming big sagebrush
Community Phase 2.1: Bluebunch wheatgrass/ Scattered Wyoming big sagebrush
This plant community is characterized by the temporary dominance of assorted native perennial bunchgrasses, primarily the caespitose form of bluebunch wheatgrass, and scattered Wyoming big sagebrush. Dominant grasses include Western wheatgrass, needle-and-thread, Indian ricegrass, prairie junegrass, and bottlebrush squirreltail. This community is typically found to occur within the first 10 years following wildfire.
Community 2.2
Yellow rabbitbrush/ Wyoming big sagebrush increasing
Community Phase 2.2: Yellow rabbitbrush/ Wyoming big sagebrush increasing
This plant community is typical approximately 30 to 40 years post wildfire, where yellow rabbitbrush is the current dominant species, and with a slight increase in Wyoming big sagebrush.
Community 2.3
Wyoming big sagebrush dominant/ Bluebunch wheatgrass & other native perennial bunchgrasses
Community Phase 2.3: Wyoming big sagebrush dominant/ Bluebunch wheatgrass & other native perennial bunchgrasses
The balance between Wyoming big sagebrush and bluebunch wheatgrass will return following at least a 40 year period since the last wildfire. Other native perennial bunchgrasses such as Western wheatgrass, needle-and-thread, Indian ricegrass, prairie junegrass, and bottlebrush squirreltail will also be present.
Pathway CP 2.1A
Community 2.1 to 2.2
Community Pathway 2.1a:
As time increases since the last wildfire, yellow rabbitbrush and Wyoming big sagebrush will increase.
Pathway CP 2.2B
Community 2.2 to 2.1
Community Pathway 2.2b:
Wildfire will reset the successional clock back to a graminoid dominated site, temporarily removing most of shrubs.
Pathway CP 2.2A
Community 2.2 to 2.3
Community Pathway 2.2a:
After approximately 40-50 years since the last wildfire, a balance between Wyoming big sagebrush and bluebunch wheatgrass will return.
Pathway CP 2.3A
Community 2.3 to 2.1
Community Pathway 2.3a
Wildfire will reset the successional clock back to a graminoid dominated site, removing the majority of the sagebrush and allowing the native perennial bunchgrass, mainly bluebunch wheatgrass, to increase and be temporarily dominant.
State 3
Wyoming Big Sagebrush Super-dominance State
The plant community that characterizes this state is a tall, dense stand of Wyoming big sagebrush with a diminished understory. The Wyoming big sagebrush will remain super-dominant as wildfire continues to be suppressed, and with heavy unrestricted grazing of livestock. The chance of wildfire has diminished due to lack of fine fuels. This State is maintained by the continuation of fire suppression and heavy livestock grazing.
Community 3.1
Wyoming big sagebrush super-dominance
Community Phase 3.1: Wyoming big sagebrush super-dominance
This plant community is dominated by tall, dense Wyoming big sagebrush that have increased at the expense of associated understory species.
State 4
Increased Invasives/ Wyoming Big Sagebrush State
Where livestock grazing has been reduced, there may be a build up of introduced annuals during years of heavy spring precipitation. The unusually wet climate can have a two-fold effect, where in some cases, soils can became anoxic; if this is followed by subsequent Aroga moth outbreak, much of the sagebrush can be killed. In other cases, an increased fine fuel loads can increase the chance of wildfire, which has the same effect of removing the sagebrush. The phases of this State pass through a period of short-term dominance by annuals (4.1), followed by a yellow rabbitbrush and native herb phase (4.2), and the eventual return of Wyoming big sagebrush with a sparser understory (4.3). Some introduced grasses that may be present in this state are Kentucky bluegrass (Poa pratensis), Bulbous bluegrass (Poa bulbosa), and smooth brome (Bromus inermis). Resiliency of this state is maintained by fire and reduced livestock grazing. As root-sprouters, yellow rabbitbrush, rhizomatous wheatgrasses, and invasive species are effective following disturbance, particularly fire. These species can out-compete fire and grazing-intolerant species. Heavy growing-season grazing will reduce site resiliency.
Community 4.1
Increased Invasives/ Wyoming Big Sagebrush State
Community Phase 4.1: Invasive annuals (mustards & cheatgrass)
Mustards and cheatgrass tend to invade after a hot, complete burn through a sagebrush community having a diminished understory component.
Community 4.2
Yellow rabbitbrush/ Native herbaceous perennials
Community Phase 4.2: Yellow rabbitbrush/ Native herbaceous perennials
This community is dominated by yellow rabbitbrush and native herbaceous perennials.
Community 4.3
Wyoming big sagebrush/ Sparse mixed understory
Community Phase 4.3: Wyoming big sagebrush/ Sparse mixed understory
This community is dominated by Wyoming big sagebrush and has a sparse mix of understory species.
Pathway CP 4.1A
Community 4.1 to 4.2
Community Pathway 4.1a:
Community Phase 4.1 will move towards Community Phase 4.2 after 10-15 years as invasive annuals are replaced by (re-sprouting) rabbitbrush and herbaceous perennials if fire does not return to the site, and with light livestock grazing.
Pathway CP 4.2B
Community 4.2 to 4.1
Community Pathway 4.2b:
A hot fire will convert Community Phase 4.2 into an invasive annuals-dominated site (4.1). Community Phase 4.1 can be effectively maintained if fire re-occurs every 2-3 years.
Pathway CP 4.2A
Community 4.2 to 4.3
Community Pathway 4.2a:
Community Phase 4.2 will move towards Community Phase 4.3 as Wyoming big sagebrush re-invades the site and a more diverse understory develops in the absence of fire, and with light livestock grazing.
Pathway CP 4.3A
Community 4.3 to 4.1
Community Pathway 4.3a:
A cool wildfire will reduce the sagebrush component (or set back its re-invasion of the site), allow for (re-sprouting) yellow rabbitbrush to dominate, and reduce understory (herbaceous) species diversity.
Pathway CP 4.3B
Community 4.3 to 4.2
Community Pathway 4.3b:
A hot wildfire will remove sagebrush and allow invasive annuals to dominate the site.
State 5
Crested Wheatgrass State
Crested wheatgrass (5.1) will be found on sites where it has been planted to provide a higher level of productivity. To keep the shrubs from re-invading, it may be necessary to follow up with additional chemical or mechanical treatment (5.1a). This resiliency of this State can be maintained by moderate livestock grazing, but excessive livestock grazing will reduce its resiliency.
Community 5.1
Crested wheatgrass
Community Phase 5.1: crested wheatgrass
This plant community is characterized by a crested wheatgrass monoculture.
Community Pathway 5.1a:
Maintenance of this state requires retreatment of the brush using chemicals or plowing to maintain grass dominance and remove re-invaded shrubs.
State 6
Wyoming Big Sagebrush/ Native Grass State
The state is achieved following a prescribed grazing regime where sheep are used during fall months (with nutrient supplementation) with the intention of reducing the shrub component to allow re-growth of native grasses (Woodland, 2008). This state can be maintained by continuing fall sheep grazing only over several years. A return to growing-season grazing too soon (before establishment of a productive native perennial grass understory) will reduce the resiliency of this State.
Community 6.1
Reduced Wyoming big sagebrush/ increased native perennial grasses/ short occupancy of cheatgrass
Community Phase 6.1: Reduced Wyoming big sagebrush/ increased native perennial grasses/ short occupancy of cheatgrass
This plant community is characterized by Wyoming big sagebrush with native perennial grass understory.
Transition T1A
State 1 to 2
Transition T1a: from State 1 to State 2 (Reference State to Wyoming Big Sagebrush/ Caespitose Bluebunch Wheatgrass/ 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 (Wyoming Big Sagebrush/ Caespitose Bluebunch Wheatgrass/ Introduced Non-natives State to Wyoming Big Sagebrush Super-dominance State)
The major driving factors behind this transition include a period of fire suppression following Euro-American settlement, allowing the sagebrush component to increase in age, height, and density. This, combined with heavy, near year-around grazing by cattle and horses, results in a diminishment of the graminoids. Subsequent use by sheep results in further loss of the native forb component. The approach to this transition is indicated by an increase in sagebrush dominance, a decrease in graminoids and/or forbs, and a reduction in microphytic soil crust. This transition is triggered by heavy season-long livestock grazing. A return to State 2 is unlikely if the seed sources of desirable understory species are depleted and/or accelerated soil erosion has ensued.
Transition T3A
State 3 to 4
Transition T3a: from State 3 to State 4 (Wyoming Big Sagebrush Super-dominance State to Increased Invasives/ Wyoming Big Sagebrush State)
The combined effect of reduced grazing followed by an unusually wet climate can create an environment where sagebrush is temporarily killed off by either: 1) the presence of anoxic soils followed by an Aroga moth outbreak (or other pathogen), or 2) wildfire carried by a buildup of fine fuels developed in response to the increased moisture. The approach to this transition is indicated by an increase in the abundance of invasive species. A return from State 4 to State 3 may be possible with long-term protection of the site from both grazing and wildfire.
Transition T3B
State 3 to 5
Transition T3b: from State 3 to State 5 (Wyoming Big Sagebrush Super-dominance State to Crested Wheatgrass State)
Land managers unhappy with diminished herbage production in State 3 can opt for mechanical or chemical removal of shrubs and seeding with crested wheatgrass. This requires, however, occasional reduction of re-invading brush by chemical or mechanical means.
Transition T3C
State 3 to 6
Transition T3c: from State 3 to State 6 (Wyoming Big Sagebrush Super-dominance State to Wyoming Big Sagebrush/ Native Grass State)
A cheaper alternative to improved forage production from State 3 is possible with supplemental fall sheep grazing to reduce sagebrush dominance and release of understory species (Woodland, 2007). Cheatgrass has a short period of temporary importance under Rich County conditions (Woodland 2007).
Transition T4A
State 4 to 5
Transition T4a: from State 4 to State 5 (Increased Invasives/ Wyoming Big Sagebrush State to Crested Wheatgrass State)
The Increased Invasives/ Wyoming Big Sagebrush State will transition to the Crested Wheatgrass State following brush management through chemical or mechanical means, and later plow and cropping into a crested wheatgrass monoculture.
Transition T4B
State 4 to 6
Transition T4b: from State 4 to State 6 (Increased Invasives/ Wyoming Big Sagebrush State to Wyoming Big Sagebrush/ Native Grass State)
The Increased Invasives/ Wyoming Big Sagebrush State can transition to the Wyoming Big Sagebrush/ Native Grass State if soils are mostly intact and seeds of desirable species are trampled into the soil during fall sheep use of the site. This strategy is risky; the desired outcome may not be achieved.
Transition T5A
State 5 to 6
Brush control and plowing of crested wheatgrass stand
