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 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
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 major influences during the Reference State would have been time since the last fire, Aroga moth, or snow mold outbreak. Thus three phases have been proposed to reflect these influences on resetting the successional clock. The basin big sagebrush (Artemisia tridentata ssp. tridentata) dominated community type with rich herb understory (1.1) would have been the most common phase found 10 to 30 years following the last fire. In this community, both cover- and production-based dominance would have been primarily from basin big sagebrush, but with a relatively rich understory of perennial herbs. The dominant grasses would have been the rhizomatous variant of bluebunch wheatgrass (Pseudoroegneria spicata) and western wheatgrass (Pascopyrum smithii). Other grasses would have included the small bluegrasses (Poa spp.) and bottlebrush squirreltail (Elymus elymoides). The dominant forbs would have likely been an assortment of buckwheats (Erigonum spp.), biscuitroots (Lomatium spp.), fleabanes (Erigeron spp.), granite prickly phlox (Linanthus pungens) and milkvetch (Astragalus spp.). 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. A recent fire, Aroga moth, or snowmold outbreak would have created a pathway (1.1a) toward temporary bunchgrass dominance (1.2). Freedom from fire, insect, or pathogens for 4 to 5 decades (1.1c) would have lead (1.1) to a phase where tall, dense sagebrush dominated (1.3). A burn (1.3a) of mature sagebrush stands would also have resulted in a bunchgrass-dominated phase (1.2). The patchiness of these natural disturbances would have created a mosaic of all three phases across the landscape where this ESD occurred.
Community 1.1
Basin big sagebrush/ abundant herbaceous understory
Community Phase 1.1: basin big sagebrush/ abundant herbaceous understory
This community was characterized by the co-dominance of shrubs, primarily basin big sagebrush, and native perennial herbs. Productivity would have been dependent upon the moisture availability in the vadose (above the water table) zone.
Community 1.2
Native perennial bunchgrass
Community Phase 1.2: native perennial bunchgrass
This was a temporary grassland variant of this plant community, dominated by the caespitose form of bluebunch wheatgrass. This community would have occurred shortly following wildfire or a sagebrush-killing pathogen outbreak, and would have existed for approximately a decade.
Community 1.3
Tall dense basin big sagebrush
Community Phase 1.3: tall dense basin big sagebrush
This community would have been characterized by a dense, tall stand of basin big sagebrush with a slightly diminished understory component.
Pathway 1.1A
Community 1.1 to 1.2
Community Pathway 1.1a
Wildfire would have temporarily created a grassland variant of the plant community.
Community Pathway 1.1b
Unusually wet periods (e.g. El Nino Southern Oscillation) would have caused temporary soil anoxia, killing the sagebrush. Similar effects would have occurred from the outbreak of Aroga moth or snow mold. This would have temporarily created a grassland variant of this plant community.
Pathway 1.1B
Community 1.1 to 1.3
Community Pathway 1.1c
Forty or more years without fire or other natural disturbances would have promoted an increase in basin big sagebrush, creating a taller, denser stand.
Pathway 1.2A
Community 1.2 to 1.1
Community Pathway 1.2a
Sagebrush would have begun to re-establish after a period of approximately 10 years after a return to a normal climate (temperatures and precipitation) and without wildfire.
Pathway 1.3A
Community 1.3 to 1.2
Community Pathway 1.3a
Wildfire would have removed the shrub component, allowing the perennial herbaceous component to regain temporary dominance.
State 2
Super-dominant Basin Big Sagebrush
State 2 is similar to Phase 1.3 of State 1 except some exotic species of both plants and animals have been introduced. Native Americans, along with their horses and burning practices, have been eliminated and climate has become warmer and the atmosphere enriched with carbon dioxide and sources of atmospheric nitrogen and sulphur. State 2 is thus a description of vegetation on this site shortly following Euro-American settlement. This state can be regarded as the current potential. The least modified plant community in State 2 is a basin big sagebrush dominated type with a less productive herbaceous understory (2.1), and with minor amounts of exotic annuals and biennials present.
The reason for the diminished understory is historic unrestricted year round livestock grazing, first by cattle and later by sheep (Parson 1996). Opening of the interspaces between the shrubs has often resulted in wind moving the fine soil particles into coppice dunes under the larger shrubs, creating mounded micro-relief and patchier nutrient reserves. This long period of pronounced removal of the herbaceous component also resulted in lengthening the fire-free interval, allowing both height and density of the sagebrush to increase more than occurred in the Reference State.
Reductions in seasons of use and intensity of livestock grazing have brought little change in this vegetation type because of the super-dominance of sagebrush and its longevity. In fact, rest from livestock use could allow for the buildup of finer, more continuous fuels, especially following wet winters and springs.
Community 2.1
Tall dense basin big sagebrush/ diminished understory
Community Phase 2.1: tall dense basin big sagebrush/ diminished understory
This phase is characterized by having tall, dense basin big sagebrush, a diminished understory, the presence of minor amounts of exotic annuals and biennials, and possibly mounded micro-relief.
State 3
Introduced Annuals & Biennials
State 3 is characterized by the dominance of several fire-prone species including cheatgrass and mustards. When fire return intervals are frequent (approximately 3 to 10 years) (3.2a) invasive annual species such as cheatgrass and mustards will predominate (3.1). Longer intervals (approximately 10 to 50 years) between fire events (3.1a) will result in a plant community dominated by biennial forbs (3.2). There is little evidence for the return of the native grasses or forbs in State 3, even if all livestock grazing is removed for decades.
Community 3.1
Invasive annuals dominant
Community Phase 3.1: invasive annuals dominant
This plant community will develop where fire return intervals are frequent. Annual species such as tall tumble mustard (Sisymbrium altissimum), cheatgrass, and Russian thistle (Salsola tragus) predominate.
Community 3.2
Biennials dominant
Community Phase 3.2: biennials dominant
This plant community will develop when intervals between fires are longer, allowing biennial species to become established. Species may include hound’s tongue (Cynoglossum spp.) and Dyer’s woad (Isatis tinctoria).
Pathway 3.1A
Community 3.1 to 3.2
Community Pathway 3.1a
Less frequent wildfire will promote a biennial forb-dominated plant community.
Pathway 3.2A
Community 3.2 to 3.1
Community Pathway 3.2a
More frequent wildfire will maintain an invasive annuals-dominated plant.
State 4
Crested Wheatgrass
State 4 is dominated by crested wheatgrass. Eventually, State 4 will be re-invaded, first by rabbitbrushes (Chrysothamnus spp.), and then whichever sagebrush has the greatest seed dispersal. Thus, if the maintenance of grass production is desired in State 4, it will require re-treatment of the brush either mechanically, chemically, or with fire (4.1a). Moderate livestock grazing will help maintain the resiliency of this state, but heavy livestock grazing will reduce its resiliency. There is little evidence for the return of the native grasses or forbs in States 3 or 4, even if all livestock grazing is removed for decades.
Community 4.1
Crested Wheatgrass State
Community Phase 4.1: crested wheatgrass
This plant community was artificially created by tilling and seeding of crested wheatgrass to increase forage for livestock.
Community Pathway 4.1a
Periodic retreatment using chemicals or mechanical means will be required to prevent woody encroachment of the crested wheatgrass seeding.
Transition T1A
State 1 to 2
Transition T1a: from State 1 to State 2 (Reference State to Super-Dominant Basin Big Sagebrush 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. In addition to these historic changes, the advent of heavy continuous year-round grazing by livestock further contributed to this transition. 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 (Super-dominant Basin Big Sagebrush State to Introduced Annuals & Biennials State)
Rest from livestock use allows the buildup of finer fuels including cheatgrass (Bromus tectorum) and mustards (Brassica, Descurainia, and/or other spp.) which could come to dominate (State 3) following wildfire (T2a).
Transition T2B
State 2 to 4
Transition T2b: from State 2 to State 4 (Super-dominant Basin Big Sagebrush State to Crested Wheatgrass State)
Because of national demands for red meat production following World War II, many of the areas in State 2 were tilled and seeded to crested wheatgrass to increase forage for livestock.
Transition T3A
State 3 to 4
Transition T3a: from State 3 to State 4 (Introduced Annuals & Biennials State to Crested Wheatgrass State)
Similarly to the impoverished sites in State 2, because of national demands for red meat production following World War II, many of the areas in State 3 were also tilled and seeded to crested wheatgrass (T3a) to increase forage for livestock, especially in areas which re-burned frequently.
