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.
Utah juniper (Juniperus osteosperma) and singleleaf pinyon (Pinus monophylla) are the dominant tree species. 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).
Fire Ecology:
Infilling by younger trees increases canopy cover causing a decrease in understory perennial vegetation and an increase in bare ground. As pinyon and juniper trees increase in density so has their litter. Phenolic compounds of juniper scales can have an inhibitory effect on grass growth (Jameson 1970). Furthermore, infilling shifts stand level biomass from ground fuels to canopy fuels which has the potential to significantly impact fire behavior. The more tree dominated pinyon and juniper woodlands become, the less likely they are to burn under moderate conditions, resulting in infrequent high intensity fires (Gruell 1999, Miller et al. 2008). Additionally, as the understory vegetation declines in vigor and density with increased canopy the seed and propagules of the understory plant community also decrease significantly. The increase in bare ground allows for the invasion of non-native annual species such as cheatgrass and with intensive wildfire the potential for conversion to annual exotics is a serious threat (Tausch 1999, Miller et al. 2008). 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.
Four possible alternative stable states have been hypothesized for this ecological site. This site is similar to 028AY099NV developed in Nevada. The state and transition model and narratives used from site 099NV and applied to 308UT (Stringham et al. 2015). The Reference State contains four community phases, shrub/grass dominated, shrub dominated, grass 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 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. An Annual State may occur, but has not been documented. 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 this ecological site prior to European settlement. It was in a natural dynamic equilibrium with the historic biotic, abiotic, climatic factors on its ecological site in North America at the time of European immigration and settlement. The dominant aspect of the plant community is pinyon pine, Utah juniper, and black sagebrush or Wyoming big sagebrush. The composition by air-dry weight is approximately 15 percent trees, 35 percent perennial grasses, 10 percent forbs, and 40 percent shrubs.
Characteristics and indicators. This state will not include any non-native species in the plant community.
Community 1.1
Old growth trees/shrubs/perennial bunchgrasses
This community phase will have widely scattered old trees with a shrub/grass understory. The dominant visual aspect of the plant community is singleleaf pinyon/Utah juniper which make up about 15 percent of the canopy cover. Trees will be rounded or flat topped. Bluebunch wheatgrass and Indian ricegrass are the dominant understory.
Table 5. Annual production by plant type
| Plant type |
Low
(lb/acre) |
Representative value
(lb/acre) |
High
(lb/acre) |
| Grass/Grasslike |
120 |
280 |
380 |
| Tree |
75 |
175 |
238 |
| Shrub/Vine |
75 |
175 |
238 |
| Forb |
30 |
70 |
95 |
| Total |
300 |
700 |
951 |
Table 6. Ground cover
| Tree foliar cover |
15%
|
| Shrub/vine/liana foliar cover |
15-30%
|
| Grass/grasslike foliar cover |
10-25%
|
| Forb foliar cover |
3-5%
|
| 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 |
– |
– |
– |
– |
| >1 <= 2 |
– |
25-35% |
20-30% |
0-10% |
| >2 <= 4.5 |
– |
– |
– |
– |
| >4.5 <= 13 |
10-20% |
– |
– |
– |
| >13 <= 40 |
– |
– |
– |
– |
| >40 <= 80 |
– |
– |
– |
– |
| >80 <= 120 |
– |
– |
– |
– |
| >120 |
– |
– |
– |
– |
Community 1.2
Bluebunch wheatgrass/pinyon and juniper seedlings/shrubs
This community phase is characterized by a post-fire shrub and herbaceous community. Bluebunch wheatgrass and other perennial grasses dominate. Forbs may increase post-fire but will likely return to pre-burn levels within a few years. Singleleaf pinyon and Utah juniper seedlings up to 20 inches in height may be present. Black sagebrush or Wyoming big sagebrush may be present in unburned patches. Burned tree skeletons may be present; however, these have little or no effect on the understory vegetation.
Community 1.3
Pinyon and juniper, young trees/perennial bunchgrasses/shrubs
This community phase is characterized as an immature woodland with pinyon, juniper trees averaging over 4 feet in height. Pinyon and juniper canopy cover is between 10 to 20 percent. Tree crowns are typically cone- or pyramidal-shaped. Understory vegetation consists of smaller tree seedling and saplings, as well as perennial bunchgrasses and sagebrush.
Community 1.4
Pinyon and juniper multiple age classes/perennial bunchgrasses/shrubs (at-risk)
This phase is dominated by Utah juniper and singleleaf pinyon. The stand exhibits mixed age classes and canopy cover exceeds 20 percent. The density and vigor of the sagebrush and perennial bunchgrass understory is decreased. Bare ground areas are likely to increase. Mat-forming forbs may increase. This community is at risk of crossing a threshold; without proper management this phase will transition to the infilled woodland state 3. This community phase is typically described as early Phase II woodland (Miller et al. 2008).
Pathway 1.1a
Community 1.1 to 1.2
A high severity crown fire will eliminate or reduce the singleleaf pinyon and Utah juniper overstory and the shrub component. This allows the perennial bunchgrasses to increase.
Pathway 1.1b
Community 1.1 to 1.4
Time without disturbance such as fire, long-term drought, or disease will allow gradual infilling of the trees.
Pathway 1.2a
Community 1.2 to 1.3
Time without disturbance such as fire, long-term drought, or disease will allow for the gradual maturation of the singleleaf pinyon and Utah Juniper component. Sagebrush reestablishes. Excessive herbivory may also reduce perennial grass understory.
Pathway 1.3a
Community 1.3 to 1.1
Fire reduces or eliminates tree canopy, allowing perennial grasses to dominate the site.
Pathway 1.3b
Community 1.3 to 1.2
Time without disturbance such as fire, long-term drought, or disease will allow for the gradual maturation of singleleaf pinyon and Utah juniper. Infilling by younger trees continues.
Pathway 1.4a
Community 1.4 to 1.1
Low intensity fire, insect infestation, or disease kills individual trees within the stand reducing canopy cover to less than 20 percent. Over time young trees mature to replace and maintain the old-growth woodland. The sagebrush and perennial bunchgrass community increases in density and vigor.
Pathway 1.4b
Community 1.4 to 1.2
A high-severity crown fire will eliminate or reduce the singleleaf pinyon and Utah juniper overstory and the shrub component which will allow for the perennial bunchgrasses to dominate the site.
State 2
Current Potential State
This state is similar to the Reference State 1, with four general community phases: an old-growth woodland phase, a shrub-herbaceous phase, an immature tree phase, and an infilled tree phase. Ecological function has not changed; however the resiliency of the state has been reduced by the presence of non-native species. These non-natives, particularly cheatgrass, can be highly flammable and promote fire where historically fire had been infrequent. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These include the presence of all structural and functional groups, low fine fuel loads and retention of organic matter and nutrients. Positive feedbacks decrease ecosystem resilience and stability of the state. These include the nonnatives’ high seed output, persistent seed bank, rapid growth rate, ability to cross pollinate, and adaptations for seed dispersal. Fires within this community with the small amount of non-native annual species present are likely still small and patchy due to low fuel loads. This fire type will create a plant community mosaic that will include all/most of the following community phases within this state.
Characteristics and indicators. This state will be similar to the Reference state except it will have non-native species in the plant communities.
Community 2.1
Old growth singleleaf pinyon and Utah juniper/sagebrush/bluebunch wheatgrass
This phase is characterized by a widely dispersed old-growth Utah juniper and singleleaf pinyon trees with an understory of sagebrush and perennial bunchgrasses. The visual aspect is dominated by singleleaf pinyon and Utah juniper which make up 10 to 25 percent of the overstory canopy cover. Trees have reached maximal or near maximal heights for the site and many tree crowns may be flat- or round-topped. Bluebunch wheatgrass and Indian ricegrass are the most prevalent grasses in the understory. Sagebrush is the primary understory shrub. Forbs, such as arrowleaf balsamroot, are minor components. Ground fires within this community are infrequent occurring on average every 15 to 25 years. This fire type will create a plant community mosaic that will include all/most of the following community phases within this state. Annual non-native species are present in trace amounts.
Community 2.2
Bluebunch wheatgrass/pinyon and juniper seedlings/shrubs
This community phase is characterized by a post-fire shrub and herbaceous community. Bluebunch wheatgrass and other perennial grasses dominate. Forbs may increase post-fire but will likely return to pre-burn levels within a few years. Pinyon and juniper seedlings up to 20 inches in height may be present. Sagebrush may be present in unburned patches. Burned tree skeletons may be present; however, these have little or no effect on the understory vegetation. Annual non-native species generally respond well after fire and may be stable or increasing within the community.
Community 2.3
Pinyon and juniper young trees/perennial bunchgrasses/shrubs
This community phase is characterized by an immature woodland, with singleleaf pinyon and Utah juniper trees averaging over 4 feet in height. Tree canopy cover is between 10 to 20 percent. Tree crowns are typically cone- or pyramidal-shaped. Understory vegetation consists of smaller tree seedling and saplings, as well as perennial bunchgrasses and shrubs. Annual nonnative species are present.
Community 2.4
Pinyon and juniper multiple age classes/perennial bunchgrasses/shrubs (at-risk)
This phase is dominated by singleleaf pinyon and Utah juniper. The stand exhibits mixed age classes and canopy cover exceeds 20 percent. The density and vigor of the sagebrush and perennial bunchgrass understory is decreased. Bare ground areas are likely to increase. Mat-forming forbs may increase. Annual non-native species are present primarily under tree canopies. This community is at risk of crossing a threshold, without proper management this phase will transition to the Infilled Tree State 3. This community phase is typically described as early Phase II woodland (Miller et al. 2008).
Pathway 2.1a
Community 2.1 to 2.2
A high-severity crown fire will eliminate or reduce the singleleaf pinyon and Utah juniper overstory and the shrub component. This allows for the perennial bunchgrasses to dominate the site.
Pathway 2.1b
Community 2.1 to 2.4
Time without disturbance such as fire, long-term drought, or disease will allow for the gradual infilling of singleleaf pinyon and Utah juniper.
Pathway 2.2a
Community 2.2 to 2.3
Time without disturbance such as fire, long-term drought, or disease will allow for the gradual maturation of the singleleaf pinyon and Utah Juniper component. Sagebrush reestablishes. Excessive herbivory may also reduce perennial grass understory.
Pathway 2.3a
Community 2.3 to 2.1
Time without disturbance such as fire, long-term drought, or disease will allow for the gradual maturation of singleleaf pinyon and Utah juniper. Infilling by younger trees continues.
Pathway 2.3b
Community 2.3 to 2.2
Fire reduces or eliminates tree canopy, allowing perennial grasses to dominate the site.
Pathway 2.4a
Community 2.4 to 2.1
Low intensity fire, insect infestation, or disease kills individual trees within the stand reducing canopy cover to less than 20 percent. Over time young trees mature to replace and maintain the old-growth woodland. The sagebrush and perennial bunchgrass community increases in density and vigor. Annual non-natives present in trace amounts.
Pathway 2.4b
Community 2.4 to 2.2
A high-severity crown fire will eliminate or reduce the singleleaf pinyon and Utah juniper overstory and the shrub component which will allow for the perennial bunchgrasses to dominate the site. Annual non-native grasses typically respond positively to fire and may increase in the post-fire community.
State 3
Infilled Tree State
This state has two community phases that are characterized by the dominance of Utah juniper and singleleaf pinyon in the overstory. This state is identifiable by over 30 percent cover of Utah juniper and singleleaf pinyon. This stand exhibits a mixed age class. Older trees are at maximal height and upper crowns may be flat-topped or rounded. Younger trees are typically cone- or pyramidal shaped. Understory vegetation is sparse due to increasing shade and competition from trees.
Community 3.1
Pinyon and juniper/invasive annuals/native perennials and shrubs
Singleleaf pinyon and Utah juniper dominate the aspect. Understory vegetation is thinning. Perennial bunchgrasses are sparse and sagebrush skeletons are as common as live shrubs due to tree competition for soil water, overstory shading, and duff accumulation. Tree canopy cover is greater than 30 percent. Annual non-native species are present or co-dominate in the understory. Bare ground areas are prevalent. This community phase is typically described as a Phase II woodland (Miller et al. 2008).
Community 3.2
Pinyon and juniper/invasive annuals
Singleleaf pinyon and Utah juniper dominate the aspect. Tree canopy cover exceeds 30 percent and may be as high as 50 percent. Understory vegetation is sparse to absent. Perennial bunchgrasses, if present exist in the dripline or under the canopy of trees. Sagebrush skeletons may be present or absent. Mat-forming forbs or Sandberg’s bluegrass may dominate interspaces. Annual nonnative species are present and are typically found under the trees. Bare ground areas are large and interconnected. Soil redistribution may be extensive. This community phase is typically described as a Phase III woodland (Miller et al. 2008).
Pathway 3.1a
Community 3.1 to 3.2
Time without disturbance such as fire, long-term drought, or disease will allow for the gradual maturation of singleleaf pinyon and Utah juniper. Infilling by younger trees continues.
State 4
Seeded State
This community is characterized by the dominance of perennial non-native species such as crested wheatgrass (Agropyron cristatum). Wyoming big sagebrush or rabbitbrush may dominate the overstory. Annual non-native species may be present in the community.
Community 4.1
Introduced non-native bunchgrasses/native shrubs
Crested wheatgrass dominates the plant community with native shrubs. Annual non-native species may be present.
Transition T1A
State 1 to 2
Trigger: Introduction of non-native annual species
Slow variables: Over time the annual non-native plants will increase within the community.
Threshold: Any amount of introduced non-native species causes an immediate decrease in the resilience of the site. Annual non-native species cannot be easily removed from the system and have the potential to significantly alter disturbance regimes from their historic range of variation.
Transition T1B
State 1 to 3
Trigger: Time and a lack of disturbance allow trees to dominate site resources; may be coupled with inappropriate grazing management that favors shrub and tree dominance.
Slow variables: Over time the abundance and size of trees will increase.
Threshold: Juniper and pinyon canopy cover is greater than 30 percent. Little understory vegetation remains due to competition with trees for site resources.
Transition T2A
State 2 to 3
Trigger: Time and a lack of disturbance allow trees to dominate site resources; may be coupled with inappropriate grazing management that favors shrub and tree dominance.
Slow variables: Over time the abundance and size of trees will increase.
Threshold: Juniper and pinyon canopy cover is greater than 30 percent. Little understory vegetation remains due to competition with trees for site resources
Transition T2B
State 2 to 4
Mechanical treatment of trees.
Restoration pathway R4A
State 3 to 2
Manual or mechanical thinning of trees coupled with seeding. Probability of success is highest from community phase 3.1.
Transition T3A
State 3 to 4
Thinning of trees coupled with seeding. Success unlikely from phase 3.2.
