Ecological dynamics

It is impossible to determine in any quantitative detail the reference state 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. 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. In the 1860’s, Europeans brought cattle and horses to the area, grazing large numbers of them on unfenced parcels year-long. 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 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.

Plant Community Narratives:
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. The dominant shrub would have been subalpine sagebrush (Artemisia spiciformis) (Shultz 2006). A lush perennial understory would have been composed of grasses including slender wheatgrass (Elymus trachycaulus), spike fescue (Leucopoa kingii), Columbia needlegrass (Achnatherum nelsonii), and nodding brome (Bromus anomalus). Forbs would have included sticky purple geranium (Geranium viscosissimum), Fendler’s meadow-rue (Thalictrum fendleri), Nevada pea (Lathyrus lanszwertii), and sulphur-flower buckwheat (Eriogonum umbellatum var. umbellatum) among many others. A more complete list of species by lifeform for the Reference State is available in accompanying tables in the “Plant Community Composition by Weight and Percentage” section of this document. The time elapsed since last wildfire would have been the driving factor behind the relative abundance of shrubs relative to the associated understory. Following a recent wildfire (1.2a), an herbaceous dominant phase would have been found (1.1). As the time since last fire increased (1.1a), the shrub component would have increased (1.2).

Community Phase 1.1: scattered subalpine sagebrush with diverse & abundant herbs
This plant community would have been a sagebrush-steppe where the herbaceous component would have been slightly greater than the shrub component. The dominant herbaceous species would have included slender wheatgrass, spike fescue, Columbia needlegrass, nodding brome, sticky purple geranium, Fendler’s meadowrue, Nevada pea, and sulphur-flower buckwheat, along with a scattering of subalpine sagebrush.

Community Pathway 1.1a:
As the length of time elapsed since the last fire lengthened the shrubs would have increased relative to the herbs.

Community Phase 1.2: subalpine sagebrush-steppe with diverse with increasing shrub dominance
This phase would have been characterized by a greater proportion of subalpine sagebrush relative to the herbs.

Community Pathway 1.2a:
Wildfire would temporarily reduce the shrub dominance allowing the native perennial grasses and forbs to dominate.

Transition T1a: from State 1 to State 2 (Reference State to subalpine Sagebrush/ Introduced Non-natives State)
The simultaneous introduction of exotic species, both plants and animals, possible extinctions of native flora and fauna, and 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, but because this plant community is particularly resilient, it may be possible to achieve a plant community that is almost identical to the Reference State.

State 2: subalpine Sagebrush/ 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 some 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 primary shrub is subalpine sagebrush. The native perennial herbs are slightly reduced due to impacts from heavy seasonal grazing, but the species would likely still include those present in the Reference State (State 1). A small component of non-native introduced annuals are now also present including Douglas’ knotweed (Polygonum douglasii), mountain tarweed (Madia glomerata), and Kentucky bluegrass (Poa pratensis). The resiliency of this State is maintained by a healthy, productive, and diverse plant community that can provide native seed sources and promotes soil stability, water infiltration, and soil moisture retention. The maintenance this State will be encouraged by a reduction in livestock grazing pressure. Conversely, continued heavy livestock grazing during the growing season will negatively impact the resiliency of this State.

Community Phase 2.1: subalpine sagebrush/diminished native perennial herbs/introduced annuals
The primary plant community in State 2 is a subalpine sagebrush-dominated site with a slightly diminished native perennial herbaceous understory. Species include slender wheatgrass, spike fescue, Columbia needlegrass, nodding brome, sticky purple geranium, Fendler’s meadow-rue, Nevada pea, and sulphur-flower buckwheat; however several introduced annual species occur as well.

Transition T2a: from State 2 to State 3 (subalpine Sagebrush/ Introduced Non-natives State to subalpine Sagebrush Super-dominance State)
Prolonged lack of fire and heavy continuous season long grazing (which occurred at many sites particularly between the 1860s and the 1950s), creates a shrub-dominated site where introduced annuals begin to replace the native herbaceous species. The approach to this transition is indicated by an increase in size, age class, and density of sagebrush and by a reduction in the understory. The trigger causing this transition is heavy growing season livestock grazing. If seed sources for desirable native species are still present, it may be possible to avoid or reverse this transition with a reduction in growing season livestock grazing.

State 3: subalpine Sagebrush Super-dominance State:
subalpine sagebrush has grown denser and taller in areas that have received nearly a century-long period of heavy livestock grazing during growing season of herbs and where fire has been suppressed (T2a). Introduced annuals such as common dandelion (Taraxacum officinale), mountain tarweed, and Douglas’ knotweed have become abundant in the understory. The stability of this less desirable State is maintained by the lack of a healthy, productive and diverse herb component capable of providing native seed source and soil moisture retention. Heavy growth-season livestock grazing will negatively impact the resiliency of this State.

Community Phase 3.1: tall & dense subalpine sagebrush/ diminished native perennial herbs/ Increasing introduced annuals
This plant community is characterized subalpine sagebrush dominance. The native perennial herbs have nearly been grazed out while several grazing-tolerant annual species have been introduced.

Transition T3a: from State 3 to State 4 (subalpine Sagebrush Super-dominance State to Managed Herbaceous State
Depending on the desired outcome and provided adequate native perennial species are still present, a the establishment of a native herbaceous community is possible through brush removal using either chemical means (i.e. 2,4-D) or prescribed fire, followed by a period of grazing deferment for at least one year, and moderate grazing thereafter.

Transition T3b: from State 3 to State 5 (subalpine Sagebrush Super-dominance State to Introduced Grassland State
On sites with lowered productivity and reduced native species, some have opted to till and re-seed with an introduced species such as orchardgrass (Dactylis glomerata), or Kentucky bluegrass (Poa pratensis) to increase forage production potential. Smooth brome (Bromus inermis) may have also been seeded to control soil erosion.

State 4: Managed Herbaceous State:
This state is dominated by native perennial herbs, either pure grasses or mixed forbs and grasses (4.1). If shrubs are removed by chemical means, the forb component will also be removed leaving only the native perennial grasses. If prescribed fire is used to remove shrubs, this will provide an equal opportunity for both grasses and forbs to respond. If keeping the shrubs back is desirable, then re-treatment using fire or chemicals may be necessary (4.1a). The resiliency of this State will be maintained by reductions in livestock grazing. Accelerated soil erosion will reduce the resiliency of this State.

Community Phase 4.1: native perennial grasses or herb dominance
This plant community is dominated by purely grasses or a mixture of native perennial forbs and grasses following brush removal by either chemical or prescribed fire, respectively.

Community Pathway 4.1a:
Re-treatment of brush by either chemical means or prescribed fire may be necessary to maintain this herbaceous State.

State 5: Introduced Grassland State:
This State is dominated by introduced grasses such as ‘Sherman’ big bluegrass (a variety of Poa ampla), smooth brome, or orchardgrass.

Community Phase 5.1: introduced grasses
Introduced grasses are dominant in this plant community.

Community Pathway 5.1a:
Re-treatment of brush by either chemical or mechanical means will be required to maintain a grass-dominated State.