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 1870’s 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 1860’s, 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 as the proportion of browse 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 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 the 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 (in the files of the State Range Conservationist) and the familiarity of rangeland relict areas where they exist. The least modified plant community (1.1) would have been a caespitose bluebunch wheatgrass (Pseudoroegneria spicata) dominated grassland with scattered perennial forbs such as buckwheat (Eriogonum spp.), fleabane (Erigeron spp.), beardtongue (Penstemon spp.), locoweed (Astragalus spp.), wild onion (Allium spp.), and western yarrow (Achillea millefolium). Other common grasses would have included needle and thread (Hesperostipa comata), Indian ricegrass (Achnatherum hymenoides), and bluegrasses (Poa spp.) Shrubs such as Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and Utah juniper (Juniperus osteosperma) would have been found on the rockiest microsites where fine fuel production was least (1.2) and thus the chances of fires reaching them low (1.1a). With fire, these woody dominated patches would have returned to the grassland-dominated phase (1.2a). 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
Caespitose Bluebunch Wheatgrass/ Perennial forbs
Community Phase 1.1: Caespitose Bluebunch Wheatgrass/ Perennial forbs
This is a sparsely vegetated grassland dominated by a caespitose form of bluebunch wheatgrass and assorted perennial forbs.
Community 1.2
Utah juniper/ Wyoming Big Sagebrush/ Sparse Perennial Forbs
Community Phase 1.2: Utah juniper/ Wyoming Big Sagebrush/ Sparse Perennial Forbs
This is a sparsely vegetated juniper savanna.
Pathway CP 1.1A
Community 1.1 to 1.2
Community Pathway 1.1a:
As time lengthens since the last wildfire, Wyoming big sagebrush and Utah juniper slowly begin to re-invade the site.
Pathway CP 1.2A
Community 1.2 to 1.1
Community Pathway 1.2a:
Wildfire would have caused the return to an herbaceous dominated phase, where bluebunch wheatgrass would be the dominant species. Perennial forbs would have included various species of buckwheat, fleabane, beardtongue, locoweed, wild onion, and western yarrow. Other common grasses would have included needle and thread and Indian ricegrass.
State 2
Utah Juniper/ Wyoming Big Sagebrush/ Depauperate Understory/ Introduced Non-natives State
State 2 is a description of the ecological site shortly following Euro-American settlement, and is considered the current potential for this site. This site was heavily utilized by livestock (first by horses and cattle, then later by sheep) almost year around (Parson 1996). Because of the close proximity of these areas to home ranches, livestock were grazed very early in the spring with some feeding and calving/lambing due to the largely southern exposures and excessive drainage to keep the animals out of mud. Especially heavy utilization during the spring quickly led to the loss of bluebunch wheatgrass and other palatable companions such as needle and thread, Indian ricegrass, and the bluegrasses (Stoddart 1940). This heavy grazing diminished the fine fuels, which, along with directed fire suppression, led to the expansion of brush first and later the juniper trees. A small component of introduced annuals were also present, but not yet dominant.
Community 2.1
Utah Juniper/ Wyoming Big Sagebrush/ Depauperate Understory/ Introduced Non-natives State
Community Phase 2.1: Depauperate Native Perennial Grasses & Forbs
This phase occurs if early, intense grazing started in phase 1.1.
Community 2.2
Wyoming Big Sagebrush Increasing/ Native Perennial Grasses & Forbs Decreasing
Community Phase 2.2: Wyoming Big Sagebrush Increasing/ Native Perennial Grasses & Forbs Decreasing
This phase occurs if early, intense, grazing started in phase 1.2.
Community 2.3
Utah Juniper Increasing/ Wyoming Big Sagebrush/ Depauperate Native Perennial Grasses & Forbs
Community Phase 2.3: Utah Juniper Increasing/ Wyoming Big Sagebrush/ Depauperate Native Perennial Grasses & Forbs
In this phase, woody plants prevail because of consumption of herbs by livestock and lack of burning.
Pathway CP 2.1A
Community 2.1 to 2.2
Community Pathway 2.1a:
Fire suppression, followed by heavy continuous season-long grazing
Pathway CP 2.2A
Community 2.2 to 2.3
Community Pathway 2.2a:
Fire suppression, simultaneous with heavy continuous season-long grazing
Pathway CP 2.3A
Community 2.3 to 2.1
Community Pathway 2.3a:
Wildfire will temporarily remove the woody plants and return the site to an herbaceous dominated phase.
State 3
Utah Juniper/ Yellow Rabbitbrush/ Invasive Annuals & Biennials State
This state is dominated by the less palatable woody plants and invasive annuals, mainly cheatgrass (Bromus tectorum), and biennials including tall tumble mustard (Sisymbrium altissimum) and tansy mustard (Descurainia spp.). Because of the steep, rocky character of this site, there are few options available to try and reverse these trends. Simply reducing grazing pressure will only result in a buildup in fuels. The potential for even more noxious plants such as Dyer’s woad (Isatis tinctoria) and knapweed (Centaurea spp.) is high. The prevention of wildfires and limiting grazing can help maintain state resiliency in the phase. Alternatively, recurring fire after a short period of recovery will reduce state resiliency.
Community 3.1
Cheatgrass & Biennial Mustards Dominant
Community Phase 3.1: Cheatgrass & Biennial Mustards Dominant
Within the first 3 to 5 years following wildfire, invasive annuals and biennial forbs will dominate the site.
Community 3.2
Yellow Rabbitbrush/ Cheatgrass & Biennial Mustards
Community Phase 3.2 Yellow Rabbitbrush/ Cheatgrass & Biennial Mustards
Approximately 5 to 15 years post fire, yellow rabbitbrush will begin to re-establish. Cheatgrass and assorted biennial mustards still characterize the understory component.
Community 3.3
Utah juniper Increasing/ Yellow Rabbitbrush/ Cheatgrass & Biennial Mustards
Community Phase 3.3: Utah juniper Increasing/ Yellow Rabbitbrush/ Cheatgrass & Biennial Mustards
Utah juniper will begin to re-establish and ultimately dominate the site as the time since last fire increases. Yellow rabbitbrush and cheatgrass are likely to be the primary understory species.
Pathway CP 3.1A
Community 3.1 to 3.2
Community Pathway 3.1a:
As the time since last fire increases, and heavy continuous season-long grazing ensues, woody species such as yellow rabbitbrush will begin to re-establish.
Pathway CP 3.2A
Community 3.2 to 3.3
Community Pathway 3.2a:
A lack of fire for more than 15 years combined with continued heavy season-long grazing will allow for re-establishment of juniper.
Pathway CP 3.3A
Community 3.3 to 3.1
Community Pathway 3.3a:
Wildfire will temporarily remove the woody plants and return the site to an herbaceous dominated phase, which will be dominated by cheatgrass or other biennial species.
Transition T1A
State 1 to 2
Transition T1a: from State 1 to State 2 (Reference State to Utah Juniper/ Wyoming Big Sagebrush/ Depauperate Understory/ 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, causes State 1 to transition to State 2.
Transition T2A
State 2 to 3
Transition T2a: from State 2 to State 3 (Utah Juniper/ Wyoming Big Sagebrush/ Depauperate Understory/ Introduced Non-natives State to Utah Juniper/ Yellow Rabbitbrush/ Invasive Annuals & Biennials State)
Although the number of livestock, and their timing of use, began to be restricted on BLM land after 1934, heavy utilization by livestock continued on private and state lands. The dominance of woody plants continued to develop. In part due to this increase in browse material, mule deer numbers greatly increased during the 1950 to 1970s. This ESD is a major part of the winter range of mule deer migrating from their summer range in Wyoming to northeast Utah. Despite many special hunts, many deer spend their winters on this ESD. Deer utilize on sagebrush in the winter and native perennial herbs in the early spring. This additional grazing impact pushes the vegetation to State 3. A key indicator of this transition is the build up of fuel. Wildfire will trigger this transition.
