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 dominant plant communities found on these sites would have depended on the time since last wildfire and activity of pocket gophers (Thomomys spp.). The first phase immediately following wildfire (1.3a) would have been dominated by a mixture of native perennial forbs and grasses including tapertip hawksbeard (Crepis acuminata), arrowleaf balsamroot (Balsamorhiza sagittata), sticky purple geranium (Geranium viscosissimum), shortstem buckwheat (Eriogonum brevicaule), bluebunch wheatgrass (Pseudoroegneria spicata), slender wheatgrass (Elymus trachycaulus), and Letterman’s needlegrass (Achnatherum lettermanii) (1.1). When present, pocket gophers would have substantially reduced the forb component (1.1a) creating a grass-dominated phase (1.2). With increased time since the last wildfire (1.2a), mountain big sagebrush (Artemisia tridentata spp. vaseyana) would have ultimately regained its dominance on the site (1.3). Several other mountain shrub species would have also been present including antelope bitterbrush (Purshia tridentata) and mountain snowberry (Symphoricarpos oreophilus). 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
native perennial forbs and grasses
This plant community would have been dominated by a mixture of native perennial forbs and grasses following wildfire. Dominant forbs would have included tapertip hawksbeard, arrowleaf balsamroot, sticky purple geranium, and shortstem buckwheat. Grasses would have included bluebunch wheatgrass, slender wheatgrass, and Letterman’s needlegrass.
Table 5. Annual production by plant type
| Plant type |
Low
(lb/acre) |
Representative value
(lb/acre) |
High
(lb/acre) |
| Grass/Grasslike |
585 |
943 |
1138 |
| Shrub/Vine |
225 |
363 |
438 |
| Forb |
90 |
145 |
175 |
| Total |
900 |
1451 |
1751 |
Table 6. Ground cover
| Tree foliar cover |
0%
|
| Shrub/vine/liana foliar cover |
14-16%
|
| Grass/grasslike foliar cover |
44-46%
|
| Forb foliar cover |
9-11%
|
| Non-vascular plants |
0%
|
| Biological crusts |
0%
|
| Litter |
0%
|
| Surface fragments >0.25" and <=3" |
0%
|
| Surface fragments >3" |
0%
|
| Bedrock |
0%
|
| Water |
0%
|
| Bare ground |
0%
|
Table 7. Canopy structure (% cover)
| Height Above Ground (ft) |
Tree |
Shrub/Vine |
Grass/
Grasslike |
Forb |
| <0.5 |
– |
– |
– |
– |
| >0.5 <= 1 |
– |
– |
– |
9-11% |
| >1 <= 2 |
– |
– |
44-46% |
– |
| >2 <= 4.5 |
– |
14-16% |
– |
– |
| >4.5 <= 13 |
– |
– |
– |
– |
| >13 <= 40 |
– |
– |
– |
– |
| >40 <= 80 |
– |
– |
– |
– |
| >80 <= 120 |
– |
– |
– |
– |
| >120 |
– |
– |
– |
– |
Community 1.2
native perennial grasses
This plant community would have been grass-dominated following heavy utilization by pocket gophers. Dominant grasses would have been bluebunch wheatgrass, slender wheatgrass, and Letterman’s needlegrass.
Community 1.3
mountain big sagebrush dominated
Mountain big sagebrush would have re-established on the site following 20 to 30 years without fire. The perennial forbs would have returned as well, complementing the graminoid counterpart in the understory.
Pathway 1.1a
Community 1.1 to 1.2
If an outbreak of pocket gophers had occurred, the site would have temporarily become grass-dominated, as pocket gophers tend to consume only the freshly-rooted forb component.
Pathway 1.2a
Community 1.2 to 1.3
Absence of fire and removal of pocket gophers would have allowed both the mountain big sagebrush and the freshly-rooted forb components to return to the site.
Pathway 1.3a
Community 1.3 to 1.1
Wildfire would have removed the sagebrush, bringing the plant community back to an herbaceous phase.
State 2
Mountain Big Sagebrush/ Introduced Non-natives State
State 2 is identical 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 relative amount of shrubs, grasses, and forbs depends upon the length of time elapsed since the last wildfire and the presence of pocket gophers. Immediately following fire (2.3a), the site will be in a mixed forb-grass phase (2.1). If pocket gophers remove the forbs (2.1a), the site could become grass-dominated (2.2). Sagebrush will re-establish 20 to 30 years after fire (2.2a), becoming dominant while still retaining much of its mixed perennial herbaceous understory (2.3). Dominant grasses are western wheatgrass (Pascopyrum smithii), with slightly diminished bluebunch wheatgrass, slender wheatgrass, and Letterman’s needlegrass (compared to the Reference State). Forbs include tapertip hawksbeard, arrowleaf balsamroot, and sticky purple geranium, among others. A small component of non-native species may also occur. This State is maintained by periodic wildfire and 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 resiliency of this State can be maintained by reductions in livestock numbers and seasons of grazing, but heavy continued grazing during the growing season will negatively impact the resiliency of this State.
Community 2.1
native perennial forbs & grasses
This plant community is dominated by a mixture of native perennial forbs and grasses following wildfire. Dominant forbs include tapertip hawksbeard, arrowleaf balsamroot, sticky purple geranium, and shortstem buckwheat. Grasses include bluebunch wheatgrass, slender wheatgrass, and Letterman’s needlegrass.
Community 2.2
Native perennial grasses
This plant community will become a grass-dominated following heavy utilization by pocket gophers. Dominant grasses will be bluebunch wheatgrass, slender wheatgrass, and Letterman’s needlegrass.
Community 2.3
mountain big sagebrush dominated
Mountain big sagebrush will re-establish on the site following a period of 20 to 30 years without fire. The perennial forbs will return as well, complementing the graminoid counterpart in the understory.
Pathway 2.1a
Community 2.1 to 2.2
If an outbreak of pocket gophers occurs, the site will become grass-dominated, as pocket gophers tend to favor the freshly-rooted forb component.
Pathway 2.2a
Community 2.2 to 2.3
Absence of fire and removal of pocket gophers will allow both the mountain big sagebrush and forb components to return to the site
Pathway 2.3a
Community 2.3 to 2.1
Wildfire will remove the sagebrush, bringing the plant community back to an herbaceous phase.
State 3
Mountain Big Sagebrush Super-dominance State
In the absence of fire, and with continued heavy impacts from livestock grazing, the native herbaceous understory will markedly decrease, allowing the shrubs, mainly mountain big sagebrush, to become super-dominant and take over the site (3.1). The stability of this State is maintained by an abundance of mountain big sagebrush seed source and a lack of native perennial herb seed source. The paucity of the herbaceous understory may allow accelerated soil erosion to occur. The resiliency of this State can be maintained by reductions in livestock numbers and seasons of grazing, but heavy continued grazing during the growing season will negatively impact the resiliency of this State.
Community 3.1
tall dense mountain big sagebrush/ depauperate herbaceous understory
This plant community is characterized by a dramatic increase in mountain big sagebrush and a corresponding reduction in the perennial herbaceous understory.
State 4
Native Perennial Grasses State
Native perennial grasses such as western wheatgrass and Letterman’s needlegrass will temporarily dominate the site (4.1) if chemicals (e.g. 2, 4-D™) are used to reduce the shrub and forb components. This grassland can be sustained by re-application of chemical, re-seeding with native seed when necessary, and moderating the livestock grazing during the growing season of the grasses (4.1a). Continued heavy livestock grazing will negatively impact the resiliency of this State.
Community 4.1
increased perennial grasses/ scattered shrubs
This plant community is dominated by native perennial grasses such as western wheatgrass and Letterman’s needlegrass released from competition by the chemical reduction of mountain big sagebrush.
State 5
Mountain big sagebrush / Unpalatable forbs state
If heavy livestock grazing continues, the grasses will be depleted once again, allowing the sagebrush and unpalatable forbs to regain dominance. The approach to this transition is indicated by an increase in sagebrush seedlings, a loss of perennial grasses, and an increase in unpalatable forbs. This transition is triggered by heavy livestock grazing and fire exclusion.
Community 5.1
Mountain big sagebrush and unpalatable forbs increase.
With heavy continued season-long grazing perennial bunchgrass species such as bluebunch wheatgrass and slender wheatgrass will dramatically decrease. This will give the ecological advantage (space and soil moisture) for mountain big sagebrush and unpalatable forbs to dominate the site.
State 6
Yellow rabbitbrush State
Yellow rabbitbrush and some common disturbance-following herbaceous species such as houndstongue (Cynoglossum spp.), tarweed (Madia spp.), and mule-ears (Wyethia amplexicaulis) will increase following fire (6.1), whether prescribed or wild, and chemical removal of mountain big sagebrush. This State could be maintained by periodic fire.
Community 6.1
yellow rabbitbrush/ increased herbs
This plant community is dominated by yellow rabbitbrush and a suite of hearty herbaceous disturbance followers such as snakeweed (Gutierrezia spp.), houndstongue, tarweed, mule-ears, and knotweed (Polygonum spp.).
State 7
Utah Juniper Invaded State
If the suppression of wildfire continues, particularly during droughty periods, and neighboring stands of Utah juniper exist, juniper will eventually move into these sites. Mountain big sagebrush and other lower shrubs will still be present initially, but with time will be outcompeted by the invading juniper trees (7.1). This State is maintained by juniper outcompeting understory species and by accelerated soil erosion. A cool-season prescribed burn will serve to remove juniper temporarily, allowing the understory to recover.
Community 7.1
Utah juniper encroachment/ mountain big sagebrush and other low shrubs
This community has a scattering of Utah juniper that have moved in from adjacent sites. Mountain big sagebrush and other low shrubs such as yellow rabbitbrush, alderleaf mountain mahogany (Cercocarpus montanus), and plains pricklypear (Opuntia polyacantha), will also be present.
Transition T1A
State 1 to 2
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.
Transition T2A
State 2 to 3
Lack of fire and continued heavy livestock grazing during the growing season of grasses will cause a transition to the Mountain Big Sagebrush Super-dominance State. The approach to this transition is indicated by a loss of perennial grass understory and an increase in shrub component relative to grasses and forbs. Grasses will consist of a residual population occurring closely under larger shrubs. The trigger causing this transition is sustained heavy grazing over the growth season.
Restoration pathway R3A
State 3 to 2
The Mountain Big Sagebrush Super-dominance State can be returned to the Mountain Big Sagebrush/ Introduced Non-natives State by applying a cool-season prescribed fire to remove sagebrush. This needs to be followed by a deferment of livestock grazing and reseeding of desirable species.
Transition T3A
State 3 to 4
With the application of 2, 4-D™ it may be possible to reduce the shrub layer and allow the native perennial grasses to re-establish. This seems similar to Restoration Pathway R3a described below; however the difference is that this is produced by application of herbicides which also knock out many forbs.
Transition T3B
State 3 to 6
Wildfire or brush management, either by mechanical means or prescribed fire, will temporarily remove the mountain big sagebrush. However, an increase in yellow rabbitbrush (Chrysothamnus viscidiflorus) is expected in most circumstances. The herbaceous component will also increase after fire or brush beating. The approach to this transition is indicated by an increase in rabbitbrush seedlings. The transition is triggered by wildfire or mechanical removal of sagebrush accompanied by heavy grazing.
Transition T3C
State 3 to 7
With continued suppression of fire and heavy continuous livestock grazing, the site may slowly be invaded by Utah juniper (Juniperus osteosperma). The approach to this transition is indicated by the increasing presence of juniper seedlings. This transition is triggered by overgrazing and fire exclusion.
Transition T4A
State 4 to 5
If heavy livestock grazing continues, the grasses will be depleted once again, allowing the sagebrush and unpalatable forbs to regain dominance. The approach to this transition is indicated by an increase in sagebrush seedlings, a loss of perennial grasses, and an increase in unpalatable forbs. This transition is triggered by heavy livestock grazing and fire exclusion.
