Ecological dynamics

It is impossible to determine in any quantitative detail the Historic Climax Plant Community (HCPC) 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, 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 and 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 least modified plant community would have been co-dominated by a mixture of grass and forb species (1.1), with slender wheatgrass (Elymus trachycaulus) and mule-ears (Wyethia amplexicaulis) as the primary species. 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 ESD document.

Community Phase 1.1: co-dominant grass-forb mixture/ scattered snowberry & other low shrubs
This plant community would have been characterized by a co-dominance of grass and forb species. Grasses would have included slender wheatgrass, mountain brome (Bromus marginatus), basin wildrye (Leymus cinereus), sheep fescue (Festuca ovina), Columbia needlegrass (Achnatherum nelsonii), and Letterman's needlegrass (Achnatherum lettermanii). Forb species would have included mule-ears, silvery lupine (Lupinus argenteus), showy goldeneye (Heliomeris multiflora), and western mountain aster (Symphyotrichum spathulatum) among others. Mountain snowberry (Symphoricarpos oreophilus) and low sagebrush (Artemisia arbuscula) would also have been scattered throughout the site.

Transition T1a: (State 1 to State 2)
The simultaneous introduction of exotic species, both plants and animals, possible extinctions of native flora and fauna, climate change, the advent of heavy continuous season long livestock grazing, and fire prevention 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.

State 2: Shrub Steppe State
State 2 is a description of the ecological site shortly following Euro-American settlement, which has been influenced by the introduction of several non-native plants and animals, possible extinctions of native species, and a different climate. Historic heavy continuous season long grazing by livestock and the prevention of wildfire also had a major impact on these sites creating a shrub steppe which should now be considered the present potential. Unpalatable species such as mule-ears and native woody species such as mountain snowberry, silver sagebrush (Artemisia cana), and low sagebrush increased while the palatable herbaceous species diminished.

Community Phase 2.1: snowberry & sagebrush increased/ palatable grasses & forbs depleted
This plant community is characterized by a relative increase in native woody species such as snowberry, low sagebrush, and silver sagebrush and unpalatable forbs, particularly mule-ears.

Transition T2a: (State 2 to State 3)
Mechanical disturbance of woody species and continued heavy livestock grazing during the growing season of grasses will cause a transition from State 2 to a perennial forb and annual grass-dominated state (State 3). The churning clay soils naturally favor herbs over woody species, thus shrubs are a temporary occupier of such sites. However both the mechanical and herbivory of interzonal grazing can trigger the shrubs which are moderately palatable, especially to sheep. Mule-ears is however, unpalatable to all animals and its massive root structure allows it to prevail under all treatments except deep plowing and/or herbicides. Reducing livestock grazing has little effect on reducing its competitive hold. The only potential restoration pathway requires massive tillage with subsequent herbicide and re-seeding efforts to convert these sites to perennial grasslands.

State 3: Perennial Forb & Annual Grass State
With continued impacts from heavy livestock grazing and mechanical, herbicidal, or fire removal of native shrubs, the native grass component will markedly decrease or be absent, shrubs will also be reduced to absence, but perennial forbs and annual grasses such as mule-ears, tarweed , (Madia glomerata) and cheatgrass (Bromus tectorum) will increase.

Community Phase 3.1: mule-ears/ tarweed/ annual grasses
This plant community is characterized by a suite of very grazing-tolerant herbaceous species such as mule-ears, tarweed, and cheatgrass.