Ecological dynamics
The Reference Plant Community is dominated by Idaho fescue, bluebunch wheatgrass and mountain big sagebrush. Subdominant species include basin big sagebrush, antelope bitterbrush and Sandberg bluegrass. Total annual production is 1400 lbs/acre in a normal year, 1600 lbs/acre in a favorable year, and 1200 lbs/acre in a unfavorable year. Structurally, shallow rooted bunchgrasses are dominant, followed by shrubs, and perennial forbs. The dominant visual aspect of this site is sagebrush with mixed grasses. Composition by weight is approximately 80 percent grasses, 5 percent forbs and 15 percent shrubs.
Herbivory has historically occurred on the site at low levels of utilization. Native herbivores include pronghorn antelope, elk, mule deer, sage grouse, lagomorphs and rodents. Livestock grazing has become prevalent across this site. Overutilization of resources due to grazing (from livestock, wildlife, and feral horses) can degrade the site and decrease forage availability and quality. This will lead to a decrease in perennial bunch grasses and an increase of invasive species (Williamson, 2020). Annual and perennial invasive species compete with desirable plants for moisture and nutrients.
Wildfire frequency across this site has historically been low. Sagebrush evolved with low intensity wildfire that left a mosaic of burned and unburned patches (Baker, 2006). Annual species such as cheatgrass and medusahead can be troublesome invaders on this site after wildfire, preventing perennial grass and shrub re-establishment. Invasive, annual plant communities increase wildfire frequency and intensity (Haubensak, 2009). This could cause the dominate shrub population to shift away from scabland sagebrush to a shrub population with quicker establishment.
High annual precipitation will increase the total plant production. Higher wildfire frequency following annual plant production can be expected due to a larger fuel load (Pilliod, 2017). Extended periods of drought significantly impact this site because of the grasses and shrubs that depend on annual moisture and the shallow soil. Extended drought reduces the vigor of perennial grasses and shrubs, while extreme drought may cause plant mortality. Extreme drought could also cause a state change that will favor bunch grasses over shrubs. Runoff potential following large precipitation events is high. Decreased infiltration, increased runoff, and increased erosion often occur when sagebrush is removed by frequent wildfires (Williams, 2018).
State 1
Reference State
The Reference State is a representative of the natural range of variability under pristine conditions. State dynamics are maintained by interactions between climatic patterns and disturbance regimes. 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. Plant community phase changes are primarily driven by fire, periodic drought and/or insect or disease attack.
Community 1.1
This community phase is characteristic of a mid-seral plant community and is dominated by sagebrush and native perennial grasses.
Potential vegetative composition by weight is about 80 percent grasses, 5 percent forbs and 15 percent shrubs. Total vegetative cover averages 60 to 70 percent.
Table 5. Annual production by plant type
| Plant type |
Low
(kg/hectare) |
Representative value
(kg/hectare) |
High
(kg/hectare) |
| Grass/Grasslike |
1076 |
1255 |
1435 |
| Shrub/Vine |
202 |
235 |
269 |
| Forb |
67 |
78 |
90 |
| Total |
1345 |
1568 |
1794 |
Community 1.2
This community phase is characterized by a post-disturbance, early seral, plant community. Sagebrush and other shrubs are reduced, or patchy. Perennial bunchgrasses and forbs dominate the visual aspect of the plant community.
Disturbance tolerant shrubs will sprout from the root-crown following low and medium intensity wildfire and may begin to dominate the plant community 2 to 5 years post-disturbance.
Community 1.3
Absence of disturbance allows sagebrush to mature and dominate the plant community. Perennial bunchgrasses and forbs are reduced in both vigor and productivity due to competition for light, moisture and nutrient resources.
Pathway 1.1a
Community 1.1 to 1.2
Wildfire.
Low severity wildfire creates a sagebrush/grass mosaic; higher intensity wildfires significantly reduce sagebrush cover and lead to early seral community dominated by grasses and forbs.
Frequency and intensity of wildfire is primarily driven by cover and amount of herbaceous vegetation. Under the reference state conditions, wildfire return intervals are estimated to be between 20 and 50 years.
Pathway 1.1b
Community 1.1 to 1.3
Time, absence of disturbance, and natural regeneration over time allows sagebrush to dominate site resources. This community phase pathway may be coupled with drought and/or herbivory further reducing herbaceous understory.
Pathway 1.2a
Community 1.2 to 1.1
Time, absence of disturbance and natural regeneration over time allows sagebrush to recover. Recovery of sagebrush depends on the availability of a local seed source (patches of mature shrubs) as well as precipitation patterns favorable for germination and seedling recruitment. Sagebrush seedlings are susceptible to less than favorable conditions for several years. Completion of this community phase pathways may take decades.
Pathway 1.3a
Community 1.3 to 1.1
Low intensity, patchy wildfire or insect infestation would reduce sagebrush overstory creating a mosaic on the landscape. Perennial bunchgrasses and forbs dominate disturbed patches due to an increase in light, moisture and nutrient resources.
Pathway 1.3b
Community 1.3 to 1.2
Widespread wildfire removes sagebrush and allows perennial bunchgrasses and forbs to dominate.
State 2
Current Potential
This state is similar to the Reference State 1.0. Ecological function has not changed, however the resiliency of the state has been reduced by the presence of invasive weeds. This state has the same three general community phases. These non-natives can be highly flammable, and can 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 non-natives’ high seed output, persistent seed bank, rapid growth rate, ability to cross pollinate and adaptations for seed dispersal.
Management would be to maintain high diversity of desired species to promote organic matter inputs and prevent the dispersal and seed production of the non-native invasive species.
Community 2.1
This community phase is similar to the Reference State Community Phase 1.1, with the presence of non-native species in trace amounts.
Resilience management. The presence of non-native annuals has reduced site resilience. Management actions should focus on maintaining the presence of all functional and structural groups and minimizing wildfire and soil disturbing practices.
Community 2.2
This community phase is characteristic of a post-disturbance, early seral community where annual non-native species are present. Perennial bunchgrasses and forbs recover rapidly following wildfire. Annual non-native species are stable or increasing within the community. Disturbance tolerant shrubs typically recover 2 to 5 years post wildfire and may dominate the sites for many years.
Community 2.3
This community phase is characterized by decadent sagebrush, reduced perennial bunchgrass and increasing bare ground. Annual non-natives species are stable or increasing due to lack of competition from perennial bunchgrasses. Shallow-rooted bunchgrasses may increase and become co-dominate with remaining deep-rooted bunchgrasses.
Pathway 2.1a
Community 2.1 to 2.2
Wildfire reduces the shrub overstory and allows for perennial bunchgrasses to dominate the site. Wildfire may be patchy, resulting in a mosaic pattern with patches of mature sagebrush remaining. Annual non-native species are likely to increase after wildfire.
Pathway 2.1b
Community 2.1 to 2.3
Time and lack of disturbance allows for sagebrush to increase and become decadent. Mature sagebrush is controlling the spatial and temporal distribution of moisture, nutrient and light resources. Native perennial bunchgrasses are reduced due to competition for these resources. Non-native annuals are stable to increasing.
Pathway 2.1a
Community 2.2 to 2.1
Time, lack of disturbance and natural regeneration of sagebrush. The establishment of sagebrush depends on presence of seed source and favorable weather patterns. It may take decades for sagebrush to recover to pre-disturbance levels.
Pathway 2.3a
Community 2.3 to 2.1
Low intensity wildfire, insect infestation, or brush management with minimal soil disturbance reduces sagebrush overstory and releases herbaceous understory.
Pathway 2.3b
Community 2.3 to 2.2
Wildfire reduces or eliminates the overstory of sagebrush and allows for the understory perennial grasses and forbs to increase. Annual non-native species respond well to wildfire and may increase post-burn.
State 3
Annual State
Annual non-natives dominated site productivity and site resources. The dominance of non-native annuals control the spatial and temporal distribution of soil moisture, soil nutrients and energy resources. Remaining patches of sagebrush and/or perennial bunchgrass suffer from increased competition and narrowed fire return intervals.
Characteristics and indicators. This state experiences frequent fire due to increased cover and continuity of fine fuels. Fire is frequent enough to prevent the recovery of long-lived native perennials like sagebrush. Disturbance tolerant shrubs may be present or increasing depending on time since disturbance.
Community 3.1
This community phase in dominated by annual non-native grasses and shallow-rooted perennial grasses. Sprouting shrubs may also be common. Patches of mature sagebrush may or may not be present.
Community 3.2
This community phase is characteristic of a post-wildfire community where annual non-natives are controlling site resources. Depending on season and/or intensity of fire the visually aspect of the site in dominated annual non-natives and bare ground. Site may be experiencing soil loss.
Resilience management. This community phases is high susceptible to frequent and repeated wildfire. Best management practices prevent sites from reaching this community phase. Management options are extremely limited.
Pathway 3.1a
Community 3.1 to 3.2
Fire reduces or eliminates the overstory shrubs and shallow-rooted perennials and allows for annual non-natives to increase
Pathway 3.2a
Community 3.2 to 3.1
Time and lack of fire allows for sagebrush and other shrubs to establish. Probability of sagebrush establishment is very unlikely and dependent on a near-by seed source from unburned patches of sagebrush.
Transition T1
State 1 to 2
Trigger: Introduction of annual non-native species
Slow variable: Over time the annual non-native plants 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 T3
State 2 to 3
Trigger: Repeated, widespread, and severe wildfire.
Slow variables: Increased production and cover of non-native annual species over time.
Threshold: Loss of deep-rooted perennial bunchgrasses and shrubs truncates, spatially and temporally, nutrient capture and cycling within the community.
Restoration pathway R2
State 3 to 2
Seeding with native species followed by prescribed grazing
Minimize soil disturbance and maximize non-native annual plant biomass removal during early spring. Combine prescribed grazing with seeding of native species. Continue to protect site from wildfire.
