Ecological dynamics
These plant communities may not represent every possibility, but they are the most prevalent and repeatable plant communities. As more data is collected, some of these plant communities may be revised or removed and new ones may be added. None of these plant communities should necessarily be thought of as the “desired plant community”. According to the USDA NRCS National Range and Pasture Handbook, the desired plant community will be determined by the decision makers and will meet minimum quality criteria established by the NRCS. The main purpose for including any description of a plant community here is to capture the current knowledge and experience at the time of this revision.
The Upland Loam (Wyoming Big Sagebrush) ecological site is dominated by perennial deep rooted cool season bunchgrasses and deep-rooted shrubs. Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) is the dominant shrub and the perennial bunchgrasses that are co-dominant with the shrubs include bluebunch wheatgrass (Pseudorogenaria spicata) and Indian ricegrass (Achnatherum hymenoides). These species generally have somewhat shallower root systems than the shrubs, but root densities are often as high as or higher than those of shrubs in the upper 0.5 m but taper off more rapidly than shrubs. General differences in root depth distributions between grasses and shrubs result in resource partitioning in these shrub/grass systems.
Utah juniper (Juniperus osteosperma) and singleleaf pinyon (Pinus monophylla) may be present on this site due to the proximity of the pinyon/juniper zone. This site is vulnerable to an increase in both pinyon and juniper trees without disturbances that keep the tree densities lower (i.e. fire). Singleleaf pinyon and Utah juniper may dominate the site if there is time without disturbances and eventually out-compete mountain big sagebrush for water and sunlight, severely reducing both the shrub and herbaceous understory (Miller et al. 2000, Lett and Knapp 2005). Bluegrasses may remain underneath trees on north-facing slopes. The potential for soil erosion increases as the Utah juniper woodland matures and the understory plant community cover declines (Pierson et al. 2010).
This ecological site has low resilience to disturbance and low resistance to invasion (Miller et al. 2015). Resilience increases with elevation, aspect, increased precipitation, and increased nutrient availability. Long-term disturbance response may be influenced by small differences in landscape topography. Concave areas receive run-in from adjacent landscapes and consequently retain more moisture to support the growth of deep-rooted perennial grasses (i.e. bluebunch wheatgrass) whereas convex areas where runoff occurs are slightly less resilient and may have more shallow-rooted perennial grasses. North slopes are also more resilient than south slopes because lower soil surface temperatures operate to keep moisture content higher on northern exposures.
Fire Ecology:
Wyoming big sagebrush is killed by fire, and does not resprout (Miller et al. 2013). Plant community composition after a fire is influenced by what plants were present before the fire and their densities (Miller et al. 2013). Typically, plants that are tolerant to fire will return after the fire (this also will depend on the severity of the fire). Bluebunch wheatgrass is tolerant of fire and can reestablish to pre-fire densities within 3 years. If the density of deep-rooted perennial grasses is low before the fire, they will be low after the fire (Miller et al. 2013). Wyoming big sagebrush may never recover to pre-burn canopy cover (Miller et al. 2013). Recovery of big sagebrush is limited in the presence of cheatgrass either before or after fire (Miller et al. 2013).
The introduction of annual weedy species, like cheatgrass, may cause an increase in fire frequency and eventually lead to an annual dominated community (Miller et al. 2013). Infilling by singleleaf pinyon and Utah juniper may also occur with an extended fire return interval. Without fire or changes in management, pinyon and juniper will dominate the site and Bonneville big sagebrush will be severely reduced. The herbaceous understory will typically be reduced. The potential for soil erosion increases as the juniper woodland matures and the understory plant community cover declines. Catastrophic wildfire in juniper controlled sites may lead to an annual weed dominated site.
Livestock/Wildlife Grazing Interpretations:
Overgrazing leads to an increase in sagebrush and a decline in understory plants like bluebunch wheatgrass. Squirreltail will increase temporarily with further degradation. Invasion of annual weedy forbs and cheatgrass could occur with further grazing degradation, leading to a decline in squirreltail and an increase in bare ground. Wetter sites are more resistant to degradation and may end up having sagebrush and Sandberg bluegrass dominate the site. A combination of overgrazing and prolonged drought may lead to soil redistribution, increased bare ground and a loss in plant production. Bluebunch wheatgrass is moderately grazing tolerant but is very sensitive to defoliation during the active growth period (Blaisdell and Pechanec 1949, Laycock 1967, Anderson and Scherzinger 1975). Sandberg bluegrass may slow reestablishment of deeper rooted bunchgrass, increase under grazing pressure (Tisdale and Hironaka 1981) and is capable of co-existing with cheatgrass. Reduced bunchgrass vigor or density provides an opportunity for Sandberg bluegrass expansion and/or cheatgrass and other invasive species to occupy interspaces, leading to increased fire frequency and potentially an annual plant community. Depending on the season of use, the grazer and site conditions, either Sandberg bluegrass or cheatgrass may become the dominant understory with inappropriate grazing management. For example, Daubenmire (1970) found that heavy sheep grazing favors Sandberg bluegrass, while heavy cattle grazing favors cheatgrass.
Six possible alternative stable states have been identified for this ecological site. The Reference State contains three community phases, shrub/grass dominated, shrub dominated, and a fire tolerant phase. The primary drivers in this state are fire, drought, and/or insect of disease. The Current Potential State is like the Reference State; however, non-native species have been introduced in the system which alters the resilience and resistance of the state. The Shrub State occurs with time and lack of disturbance and/or inappropriate grazing management. The Annual State occurs after large fires or multiple fires that promote annual invasive species dominance over native shrubs and grasses. The Tree State occurs when there has been sufficient time for junipers and/or pinyon trees to increase in density and dominate the site dynamics. The Seeded State occurs with management with seeding of deep rooted perennial bunchgrasses. Specific community phases and transitions will be described in the narratives below.
State 1
Reference State
The Reference State includes the plant communities that were best adapted to the unique combination of factors associated with the ecological site. It is assumed that this site was in dynamic equilibrium with the historic biotic, abiotic, climatic factors in North America at the time of European immigration and settlement. This dominant aspect of the plant community is Wyoming big sagebrush and bluebunch wheatgrass. The community is made up of 65 percent grass, 15 percent forbs, and 20 percent shrubs based on dry weight. The community phases are interrelated and dependent on weather patterns and events as well as fire frequency and intensity. The fire frequency should be around 35 to 55 years. Any set of events that force the plant community out of this pattern can push it over a threshold and into another state (i.e. introduction of annual non-native plants).
Characteristics and indicators. This state does not have non-native species in the plant community.
Community 1.1
Wyoming big sagebrush/Perennial Cool Season Grasses ≥ Forbs ≥ Other Shrubs
The plant community is represented with 55 percent grasses, 10 percent forbs, and 35 percent shrubs. The dominant shrub is Wyoming big sagebrush. The dominant grass is bluebunch wheatgrass and the dominant forb is arrowleaf balsamroot (Balsamorhiza sagittata). This community typically has between 10 to 15 percent bare ground.
Table 5. Annual production by plant type
| Plant type |
Low
(lb/acre) |
Representative value
(lb/acre) |
High
(lb/acre) |
| Grass/Grasslike |
310 |
650 |
700 |
| Shrub/Vine |
250 |
475 |
490 |
| Forb |
90 |
100 |
110 |
| Total |
650 |
1225 |
1300 |
Table 6. Canopy structure (% cover)
| Height Above Ground (ft) |
Tree |
Shrub/Vine |
Grass/
Grasslike |
Forb |
| <0.5 |
– |
0% |
0% |
0% |
| >0.5 <= 1 |
– |
0% |
5-10% |
5-10% |
| >1 <= 2 |
– |
1-5% |
15-30% |
1-5% |
| >2 <= 4.5 |
– |
10-20% |
0-5% |
0% |
| >4.5 <= 13 |
– |
– |
– |
– |
| >13 <= 40 |
– |
– |
– |
– |
| >40 <= 80 |
– |
– |
– |
– |
| >80 <= 120 |
– |
– |
– |
– |
| >120 |
– |
– |
– |
– |
Community 1.2
Wyoming big sagebrush = Perennial Cool Season grasses ≥ Forbs ≥ Other Shrubs
The plant community occurs when there is a time between disturbance. Shrubs increase in this community phase and grasses decrease. The community composition is 45 percent grasses, 10 percent forbs, and 45 percent shrubs.
Community 1.3
Perennial Cool Season Grasses ≥ Forbs ≥ Fire Tolerant Shrubs
Wyoming big sagebrush has been removed and perennial cool season grasses dominate. Some fire tolerant shrubs may also be part of the community. The community composition is 75 percent grasses, 10 percent forbs, and 15 percent fire tolerant shrubs. There will also be about 15 to 25 percent bare ground.
Pathway 1.1a
Community 1.1 to 1.2
Time without catastrophic event. This was probably dependent on a specific chain of climatic events.
Pathway 1.1b
Community 1.1 to 1.3
Fire, insects, prolonged drought, and/or pathogens that kills and/or reduces the dominant shrub overstory. Fire is the most effective of these disturbances.
Pathway 1.2a
Community 1.2 to 1.3
Fire, insects, prolonged drought, and/or pathogens that kills and/or reduces the dominant shrub overstory. Fire is the most effective of these disturbances.
Pathway 1.3a
Community 1.3 to 1.1
Time without catastrophic event. This was probably dependent on a specific chain of climatic events.
State 2
Current Potential State
The Current Potential State (CPS) includes the biotic communities that would become established on the ecological site if all successional sequences were completed without interferences by humans under the present environmental conditions. Natural disturbances are inherent in its development. The CPS state may include acclimatized, naturalized or invasive nonnative species. There is no known way to effectively remove these plants from the site once they have become established. The level of occurrence of these plants in the CPS is such that careful management can prevent their domination of the site. This site is irreversibly changed. Plant communities within the CPS state may be managed and used for various purposes without significant alteration in plant community composition or production. It includes all the plant communities that exist in the Reference State with the inclusion of species that are non-native to this ESD.
These scenarios are very interrelated and dependent on weather patterns and events as well as fire frequency and intensity. The fire frequency should be around 30 to 55 years. Any set of events that are strong enough to force the plant community out of this pattern can push it over a threshold and push it into another state.
Characteristics and indicators. This state is similar to the Reference State except it includes non-native species in the plant community.
Community 2.1
Wyoming big sagebrush ≥ Perennial Cool Season Grass ≥ Forbs ≥ Other Native Shrubs ≥ Non-Native Species
This community is represented with 55 percent grasses, 10 percent forbs, and 35 percent shrubs. The dominant shrub is Wyoming big sagebrush. The dominant grass is bluebunch wheatgrass and the dominant forb is arrowleaf balsamroot. This community will have between 15 to 25 percent bare ground. This community will have notable amounts of non-native species.
Community 2.2
Wyoming big sagebrush = Perennial Cool Season Grasses ≥ Forbs ≥ Non-Native Species
This plant community occurs when there has been sufficient time between disturbances. Wyoming sagebrush increases and the understory decreases. The community composition is 45 percent grasses, 10 percent forbs, and 45 percent shrubs. This community typically has between 20 to 30 percent bare ground. This community will also have notable amounts of non-native species.
Community 2.3
Perennial Cool Season Grasses ≥ Forbs ≥ Fire Tolerant Shrubs ≥ Non-Native Species
Figure 6. R028AY309UT State 2 phase 2.3 Bluebunch wheatgrass
This community occurs when a fire moves through the site eliminating the Wyoming big sagebrush and other shrubs. The community composition is 75 percent grasses, 10 percent forbs, and 15 percent fire tolerant shrubs. This community will have 15 to 25 percent bare ground. This community will have notable amounts of non-native species.
Pathway 2.1a
Community 2.1 to 2.2
Time without catastrophic event. This was probably dependent on a specific chain of climatic events.
Pathway 2.1b
Community 2.1 to 2.3
Fire, insects, prolonged drought, and/or pathogens that kills and/or reduces the dominant shrub overstory. Also overgrazing with or without drought over a prolonged period of time fire and/or overgrazing are the most common of these disturbances.
Pathway 2.2a
Community 2.2 to 2.3
Fire, insects, prolonged drought, and/or pathogens that kills and/or reduces the dominant shrub overstory. Also overgrazing with or without drought over a prolonged period of time fire and/or overgrazing are the most common of these disturbances
Pathway 2.3a
Community 2.3 to 2.1
Time without catastrophic event. This was probably dependent on a specific chain of climatic events.
State 3
Utah Juniper Invasion State
The Utah Juniper Invasion State has only two described plant communities, but many variations of the represented ones are present. This state occurs when lack of disturbance, typically fire, has allowed Utah juniper and pinyon to establish and increase on the site. The Utah juniper increases and uses more resources. The juniper will eventually suppresses the shrub and grass understory. Shrubs are typically the first plants to decrease and may be found in small amounts or be absent in the community. The transition to tree dominated increases the probability of non-native annual dominance in the understory as those annual species can utilize the bare space between trees. This state may also accelerate soil erosion as the understory decreases leaving more bare ground susceptible to erosion. This state is persistent until the right conditions occur for a large wildfire. Mechanical tree removal may also occur to reduce tree cover.
Characteristics and indicators. This state will have a noticeable presence of Utah juniper in the plant community.
Community 3.1
Utah juniper Wyoming big sagebrush Native Grasses & Forbs Non-Native Invasive Annuals
Figure 7. R028AY309UT State 3 Phase 3.1 Juniper Invasion
This community has a strong overstory of Utah juniper with some One-seed pinyon but still has an
understory similar to community 2.1. The community will have around 20 to 35% bare ground. Fire could potentially reset the community back to the Current Potential State.
Community 3.2
Utah Juniper Invasive Annuals
This community is present when around 95% of the native plants have been removed from the plant community and only pinyon and juniper with a sparse understory of invasive annuals are left on the site. This community will have around 45 to 85% bare ground. If any native plants are found in the community it will be very few Sandberg bluegrass.
Pathway 3.1a
Community 3.1 to 3.2
Overgrazing with or without drought over a prolonged period of time.
Pathway 3.2a
Community 3.2 to 3.1
Fire; insects; prolonged drought; pathogens that reduce the dominant shrub overstory. Fire is the most effective of these disturbances.
State 4
Yellow rabbitbrush/invasive annuals = native perennials
The Yellow rabbitbrush/invasive annuals = native perennials state occurs when fire removes the non-fire tolerant shrubs like big sagebrush. Overgrazing can and often does enhance the effect of fire. Other things like drought can also lead toward this condition. The dominant visual aspect of this community are annual grasses (mainly cheatgrass brome) and yellow rabbitbrush. The plant community composition is 35 percent cheatgrass brome, 10 percent forbs, and 45 percent fire tolerant shrubs with 90 percent of the shrub component being yellow rabbitbrush with 10 percent native perennials. If the site continues along the above described path it will deteriorate to an annual plant community.
Characteristics and indicators. This state is dominated by shrubs other than Wyoming big sagebrush, such as rabbitbrush and broom snakeweed.
Community 4.1
Yellow rabbitbrush ≥ Invasive Annuals = Native perennials
This plant community consists of about 40 percent non-native annual grass, 40 percent yellow rabbitbrush, 8 percent other fire tolerant shrubs, 10 percent forbs, and 2 percent native perennials. A continued short fire cycle (8 to 10 years) allows this community to persist. This community has about 20 to 35 percent bare ground.
Community 4.2
Invasive Annuals
The community composition is 85 percent invasive annals, 5 percent forbs, and 5 percent native perennials with few shrubs. This community will have 25 to 40 percent bare ground.
Pathway 4.1a
Community 4.1 to 4.2
Increased fire frequency (3 to 5 years) and intensity without follow-up management. Overgrazing can create conditions that enhance this pathway.
Pathway 4.2a
Community 4.2 to 4.1
Time and management of grazing alone or along with other disturbances where human and/or naturalized introduction of native and/or introduced perennial plant species takes place.
State 5
Invasive Annual Grass State
The Invasive Annual Grass State occurs when this site is overgrazed and then burned and not seeded or has a failed seeding. The dominant aspect of the plant community is cheatgrass brome and yellow rabbitbrush. The community will usually be made up of 75 percent non-native annual grasses, 10 percent forbs (introduced or native), and 10 percent yellow rabbitbrush with minor components of other shrubs. The fire frequency in this state is 4 to 8 years.
Characteristics and indicators. This state will be dominated by invasive annual plants.
Community 5.1
Invasive Annuals = Native Perennial Grasses & Forbs ≥ Few Fire Tolerant Shrubs
This plant community consists of approximately 43 percent non-native annual grasses, 32 percent native perennials, 10 percent forbs (both native and introduced), 8 percent yellow rabbitbrush, 2 percent other fire tolerant shrubs, and 5 percent other annual grasses. A continued short fire cycle (8 – 10 years) is what is needed to make this community continue along this path. This community will have around 20 to 35 percent bare ground.
Community 5.2
Invasive Annuals
Figure 8. R028AY309UT State 5 Phase 5.2 Cheatgrass brome
This plant community consists of approximately 85 percent invasive annuals (predominately cheatgrass brome), 5 percent forbs, 5 percent native perennials, and a small component of other species. This community will have around 25 to 40 percent bare ground.
Pathway 5.1a
Community 5.1 to 5.2
Overgrazing and/or other types of disturbances that cause destruction of the perennial plants over a long period of time.
Pathway 5.2a
Community 5.2 to 5.1
Time without disturbance and/or improved management of grazing coupled with climatic events that allow native plants to establish on the site.
State 6
Seeded Range State
The Seeded Range State exists when the site is cultivated and/or burned and planted to introduced and/or in some situations native grasses with or with-out forbs and shrubs.
Characteristics and indicators. Non-native bunchgrasses and forbs dominate the plant community.
Community 6.1
Introduced Perennial Plants
The plant community consists of introduced grasses and may include introduced forbs and/or shrubs. In some situations native grasses and native forbs and/or native shrubs. Or the community could be a combination of both introduced and native plants. These plantings are often as productive as the site in the Current Potential State.
Community 6.2
Native Shrubs = Introduced Perennial Plants
This plant community occurs when management and weather conditions create the kind of episodic situation that allows Wyoming big sagebrush and other native plant species to move back onto the site.
Pathway 6.1a
Community 6.1 to 6.2
Time without catastrophic event. This was probably dependent on a specific chain of climatic events.
Pathway 6.2a
Community 6.2 to 6.1
Time and management of grazing alone or along with other disturbances where human intervention takes place to move the community back.
Transition T1a
State 1 to 2
Introduction of non-native species into the ecosystem.
Transition T1b
State 1 to 3
Introduction of Utah juniper along with the introduction of non-native species into the ecosystem. Along with prolonged drought, overgrazing, extreme lengthening of the fire interval frequency. This takes place when the sagebrush canopy increases and destroys the perennial grass and forb under story and the fire frequency is increased from 50 to 60 years to 70 to 90 years and the introduction of Utah juniper with pinyon in areas where seed for these species are available.
Transition T2a
State 2 to 3
Prolonged drought, overgrazing, extreme lengthening of the fire interval frequency. This takes place when the sagebrush canopy gets so heavy that it destroys the perennial grass and forb under story and the fire frequency is increased from 50 to 60 years to 70 to 90 years and the introduction of Utah juniper with pinyon in areas where the seed for these species are available.
Transition T2b
State 2 to 4
Overgrazing and/or increase of fire frequency over a long period, between 8 and 12 years between fires.
Transition T2c
State 2 to 5
Overgrazing and/or increase of fire frequency over a long period, between 4 and 8 years between fires.
Transition T2d
State 2 to 6
Human caused disturbance (mechanical treatment and seeding; chemical treatment and seeding. etc.)
Transition T3a
State 3 to 4
Continued overgrazing and increase of fire frequency over a very prolonged period. (8 to 12 year fire frequency interval)
Transition T3b
State 3 to 6
Human caused disturbance (mechanical treatment and seeding; chemical treatment and seeding. etc.)
Transition T4a
State 4 to 5
Time without catastrophic event and/or with management of grazing and often energy inputs. The community phase 4.2 will be self-sustaining if the fire frequency remains 3 to 5 years. This will continue unless a large amount of energy is injected into the system and management is changed..
Transition T4b
State 4 to 6
Human caused disturbance (mechanical treatment and seeding; chemical treatment and seeding. etc.)
Transition T5a
State 5 to 6
Human caused disturbance (mechanical treatment and seeding; chemical treatment and seeding etc.)
Restoration pathway R6a
State 6 to 2
Time with proper management that favors the native plants as they establish on site. This may take over 30 years. The time frame depends on management and on the precipitation amounts.
| Prescribed Grazing |
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| Grazing Management Plan - Applied |
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