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. Pre-settlement fire return intervals of 20 to 30 years tended to favor the native bunchgrasses. Under such conditions, the native plant community would have been characterized by mixed bunchgrasses and basin big sagebrush (Artemisia tridentata ssp. tridentata) (2.1). The major grasses would have included basin wildrye (Leymus cinereus), rhizomatous bluebunch wheatgrass (Pseudoroegneria spicata), bottlebrush squirreltail (Elymus elymoides), native bluegrasses (Poa secunda, Poa fendleriana), and thickspike wheatgrass (Elymus lanceolatus). Other associated woody species may have included yellow rabbitbrush (Chrysothamnus viscidiflorus) 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.
Community 1.1
Reference State
Community Phase 1.1: basin big sagebrush/ mixed bunchgrasses
The least modified plant community within the Reference State (1.1) would have been characterized by an assortment of native bunchgrasses and basin big sagebrush. Dominant grasses would have included basin wildrye, rhizomatous bluebunch wheatgrass, bottlebrush squirreltail, Poa spp., and thickspike wheatgrass.
Community 1.2
Basin big sagebrush increasing/ mixed bunchgrasses
Community Phase 1.2: basin big sagebrush increasing/ mixed bunchgrasses
Basin big sagebrush would have increased in density as long as the community had not experienced wildfire. The native bunchgrass understory would have maintained its diversity.
Pathway CP 1.1A
Community 1.1 to 1.2
Community Pathway 1.1a
Sites that experienced an absence of fire would have had an increase in basin big sagebrush along with the associated native bunchgrasses.
Pathway CP 1.2A
Community 1.2 to 1.1
Community Pathway 1.2a
Wildfire would shift the plant community back towards one dominated by mixed bunchgrasses and basin big sagebrush (2.1).
State 2
Basin Big Sagebrush/ Mixed Bunchgrass/ 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 shortly following Euro-American settlement. This State can be regarded as the current potential. The range in plant communities within this State is characterized by the relative amount of bunchgrass present, which is primarily associated with the time since last fire. With more recent fires and prescribed grazing (2.2a) the plant community would be dominated by mixed bunchgrasses and basin big sagebrush (2.1). In the absence of fire and with protection from livestock grazing (2.1a), the plant community would shift to a more basin big sagebrush dominated site, but would still have remnants of the native bunchgrass understory (2.2).
Resiliency of this State is maintained by the availability of native seed sources for both the mixed bunchgrasses and basin big sagebrush, and by wildfire. This site responds well to cool season fire and more moderate non-growing season grazing regimes provided that the seed sources for the mixed bunchgrasses are present. A pre-settlement fire return interval of 20-30 years favored the grasses. Without fire, bunchgrass diversity and production may diminish, while sagebrush may increase and ultimately outcompete the native bunchgrasses. This shift in plant community composition puts this State at greater risk in the event of a hot summer or fall fire; further degradation could occur if grazing were to be initiated immediately following such a fire. Hotter fires followed by heavy grazing could cause the replacement of the basin big sagebrush component with fire-tolerant species such as yellow rabbitbrush and rhizomatous wheatgrasses.
Community 2.1
Mixed bunchgrasses/ basin big sagebrush
Community Phase 2.1: Mixed bunchgrasses/ basin big sagebrush
This plant community (2.1) is characterized by a slight dominance of a mix of native bunchgrasses and basin big sagebrush. Grass species would include: basin wildrye, rhizomatous bluebunch wheatgrass, bottlebrush squirreltail, and Poa spp.
Community 2.2
Basin big sagebrush increasing/ mixed bunchgrasses
Community Phase 2.2: basin big sagebrush increasing/ mixed bunchgrasses
This plant community (2.2) is characterized by a slight dominance of basin big sagebrush and a native bunchgrass understory.
Pathway CP 2.1A
Community 2.1 to 2.2
Community Pathway 2.1a
Sites that have experienced very limited to no grazing and an absence of fire will have a slight dominance of basin big sagebrush along with the associated native bunchgrasses.
Pathway CP 2.2A
Community 2.2 to 2.1
Community Pathway 2.2a
A cool spring wildfire followed by prescribed grazing would shift the plant community back towards one dominated by mixed bunchgrasses and basin big sagebrush (2.1).
State 3
Basin Big Sagebrush/ Rhizomatous Wheatgrass State
State 3: Basin Big Sagebrush/ Rhizomatous Wheatgrass State
Sites where heavy continuous season-long grazing has taken place in the absence of fire will develop into a basin big sagebrush-dominated plant community accompanied by rhizomatous bluebunch and western wheatgrasses. Resiliency of this State is maintained by the absence of fire and heavy grazing during the growing season for grasses, which removes grazing-intolerant grass species (bunchgrasses) and leaves only grazing-tolerant grasses and sagebrush. The dominance of basin big sagebrush and lack of native bunchgrasses places this State at risk in the event of a hot summer or fall fire.
Community 3.1
Basin Big Sagebrush/ Rhizomatous Wheatgrass State
Community Phase 3.1: basin big sagebrush/ rhizomatous wheatgrass
This plant community (3.1) is characterized by a dominance of basin big sagebrush and rhizomatous wheatgrasses (predominantly Western wheatgrass).
State 4
Yellow Rabbitbrush/ Rhizomatous Wheatgrass State
Yellow rabbitbrush and rhizomatous wheatgrass will be found on sites that have experienced both heavy continuous season-long grazing and frequent wildfire disturbances. This is the most commonly found current State. The resiliency of this State is maintained by the ability of root-sprouting species (yellow rabbitbrush and rhizomatous wheatgrasses) to successfully establish after fire and out-compete other fire and grazing-intolerant species.
Community 4.1
Yellow Rabbitbrush/ Rhizomatous Wheatgrass State
Community Phase 4.1: yellow rabbitbrush/ rhizomatous wheatgrass
This plant community (4.1) is characterized by a dominance of yellow rabbitbrush and rhizomatous bluebunch and western wheatgrass.
Transition T1A
State 1 to 2
Transition T1a: from State 1 to State 2 (Reference State to Basin Big Sagebrush/ Mixed Bunchgrass/ 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, 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 (Basin Big Sagebrush/ Mixed Bunchgrass/ Introduced Non-natives State to Basin Big Sagebrush/ Rhizomatous Wheatgrass State)
The Mixed Bunchgrass/ Basin Big Sagebrush/ Introduced Non-natives State will transition to the Basin Big Sagebrush/ Rhizomatous Wheatgrass State in the absence of fire or with heavy grazing during the growing season of grasses, removing grazing intolerant species. The approach to this transition is indicated by an increase in basin big sagebrush cover, height, and age relative to grasses. Long periods (several decades) without fire and/or heavy grazing, especially during the growing season of grasses, will trigger the transition.
Transition T2B
State 2 to 4
Transition T2b: from State 2 to State 4 (Basin Big Sagebrush/ Mixed Bunchgrass/ Introduced Non-natives State to Yellow Rabbitbrush/ Rhizomatous Wheatgrass State)
The Mixed Bunchgrass/ Basin Big Sagebrush/ Introduced Herb State transition to the Yellow Rabbitbrush/ Rhizomatous Wheatgrass State is triggered by a relatively hot (stand-replacing) wildfire followed by heavy growing season grazing disturbances which remove remaining (post-fire) grazing intolerant grass species. The approach to this transition is indicated by an increase in basin big sagebrush cover, height, and age relative to grasses.
Restoration pathway R3A
State 3 to 2
Restoration Pathway R3a: from State 3 to State 2 (Basin Big Sagebrush/ Rhizomatous Wheatgrass State to Mixed Bunchgrass/ Basin Big Sagebrush/ Introduced Non-natives State)
It may be possible using a combination of brush management (e.g. chemicals, low tillage, mechanical methods via Lawson soil aerator, or prescribed fire), prescribed grazing, and reseeding with native bunchgrasses to restore this plant community to conditions associated with the Basin Big Sagebrush/ Mixed Bunchgrass/ Introduced Herb State (State 2).
Transition T3A
State 3 to 4
Transition 3a: from State 3 to State 4 (Basin Big Sagebrush/Rhizomatous Wheatgrass State to Yellow Rabbitbrush/ Rhizomatous Wheatgrass State)
The Basin Big Sagebrush/Rhizomatous Wheatgrass State transition to the Yellow Rabbitbrush/Rhizomatous Wheatgrass State is triggered by a hot (stand-replacing) wildfire or brush management techniques (e.g. chemical, mechanical, fire), followed by heavy grazing during growing season of the grasses in close temporal proximity. The approach to this transition is indicated by an increase in basin big sagebrush cover, height, and age, and by an increase in the continuity of understory fuels.
Restoration pathway R4A
State 4 to 2
Restoration Pathway R4a: from State 4 to State 2 (Yellow Rabbitbrush/ Rhizomatous Wheatgrass State to Basin Big Sagebrush/ Mixed Bunchgrass/ Introduced Herb State)
It may be possible using a combination of brush management (e.g. using chemicals), inter-seeding with native bunchgrasses, and prescribed grazing to restore this plant community to conditions associated with the Basin Big Sagebrush/ Mixed Bunchgrass/ Introduced Non-natives State if accelerated soil erosion or soil tillage has not taken place. Tillage eliminates the native perennial forbs, some of which are very difficult to replace because their seed is either very expensive or unavailable.
