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 moderately vegetated variant of semi-desert sagebrush with about 60 percent of the forage production from grasses, 15 percent forbs, and 15 percent woody plants, primarily from Wyoming big sagebrush (Artemisia tridentata spp. wyomingensis). The productivity would have been relatively higher than nearby non-gravelly (e.g. R034AY2ggUT Semi-desert Loam Ecological Site) because of the Inverse Texture Principle (Noy-Meir, 1973). In deserts and semi-deserts, finer textured soils are effectively drier and thus typically have lower production potential than coarser textured soils. The major grasses would have included a caespitose form of bluebunch wheatgrass (Pseudoroegneria spicata), slender wheatgrass (Elymus trachycaulus), Western wheatgrass (Pascopyrum smithii), Indian ricegrass (Achnatherum hymenoides), and needle-and-thread (Hesperostipa comata). Other grasses and grass-likes would have included prairie junegrass (Koeleria macrantha), bottlebrush squirreltail (Elymus elymoides), Sandberg bluegrass (Poa secunda), and thickspike wheatgrass (Elymus lanceolatus). Other associated woody species may have included yellow rabbitbrush (Chrysothamnus viscidiflorus), black sagebrush (Artemisia nova), 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 of these sites would have averaged approximately 400 to 700 pounds per acre. The fire return interval would have averaged approximately 20 to 25 years. The phases of this ESD 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 5 to 15 years post-fire (1.1a), followed by return to Wyoming big sagebrush dominance with a bunchgrass understory (1.3) 15 to 20 years post-fire (1.2a).
Community 1.1
Reference State
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 a caespitose form of bluebunch wheatgrass, and a scattering of 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 5 to 15 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 25 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 the length of time increased since last wildfire, (i.e. greater than 25 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 by removing the majority of the sagebrush and allowing the native perennial bunchgrass, 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 is considered 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 a caespitose form of bluebunch wheatgrass, and a scattering of 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 5 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 5 to 15 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 20 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 20 to 25 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 bunchgrasses, 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
Plant 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 Herbs State
It is possible to see a reduction in the super-dominance of sagebrush through prescribed grazing using sheep in fall months or, alternatively, following an outbreak of Aroga moth. Sheep will focus on sagebrush when no other forage is available, and Aroga moths are capable of killing off large stands of sagebrush. Reducing the sagebrush dominance could allow the native perennial grasses and forbs to re-establish in the following spring (4.1). While there has been some invasion of exotics, such as the mustards (primarily Descurainia spp. and Sisymbrium altissimun) and cheatgrass (Bromus tectorum) in this State, the examples of where they occur in Rich County are only for short periods of time unless the disturbance is continuous. This is because the Wasatch Formation from which these soils are derived had their nutrients depleted when subtropical forests of the Miocene occupied these parent materials. Persisting dominance of invasives such as cheatgrass, require the higher planes of soil nutrients available from younger, less-leached parent materials. This State can be maintained by deferring growing-season grazing in some years, but a return to intense growing-season grazing will reduce the resiliency of this State.
Community 4.1
Reduced Wyoming big sagebrush/ increased native perennial bunchgrasses & forbs
Community Phase 4.1: reduced Wyoming big sagebrush/ increased native perennial bunchgrasses & forbs
This plant community may have some decrease in Wyoming big sagebrush, but a noticeable increase in the native perennial understory.
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 tilling to maintain grass dominance and remove re-invaded shrubs.
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 several decades of fire suppression, which allows 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 a loss of understory species. This transition is triggered by heavy livestock utilization during the growing season of desirable understory species. It may be possible to restore this community (return to State 2) if accelerated soil erosion has not ensued.
Transition T3A and T3B
State 3 to 4
Transition T3a: from State 3 to State 4 (Wyoming Big Sagebrush Super-dominance State to Increased Herbs State)
Recent work by Woodland (2007) shows that the sagebrush dominance can be broken and, at minimum, the graminaceous understory can be enhanced if supplemental fall sheep grazing is employed. Recovery of the native perennial forb component will probably require simultaneous reseeding in conjunction with the supplemented sheep grazing during the fall when every plant except sagebrush is dormant.
Transition T3b: from State 3 to State 4 (Wyoming Big Sagebrush Super-dominance State to Increased Herbs State)
The transition from a Sagebrush Super-dominant State to an Increased Herb State can also take place following an outbreak of Aroga moth (Woodland 2007). This transition may be possible if accelerated soil erosion has not ensued.
Transition T3C
State 3 to 5
Transition T3c: 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.
