Stony Foothills South Aspect bitterbrush
Scenario model
Current ecosystem state
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Management practices/drivers
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- Transition T1A More details
- Transition T2A More details
- Restoration pathway R3A More details
- Restoration pathway R4A More details
- Transition T4A More details
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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Description
State 1 represents shrub steppe with no invasive or exotic weed species. All the functional, structural groups are represented by one or more native species. Reference state Community Phases: 1.1 Reference Bluebunch wheatgrass – bitterbrush 1.2 Bunchgrass Bluebunch wheatgrass 1.3 Shrub Steppe Bitterbrush – bluebunch wheatgrass 1.4 Heavy Shrub Bitterbrush – needle and thread Communities 1.1, 1,2 and 1.3 can shift to the other two communities and back again. Dominate Reference State Species: Antelope bitterbrush – bluebunch wheatgrass At-risk Communities: • All communities in the reference state are at risk of moving to State 2. The seed source of cheatgrass is nearby and blowing onto most sites annually • Community Phases 1.1, 1.2 and 1.3 have high amounts of bluebunch wheatgrass cover and are at low risk of moving to State 3 • Community Phase 1.4 is at-risk because of low density for bluebunch wheatgrass. Community 1.4 should be seeded after fire • Any community with more than 40 percent bitterbrush cover • When fire kills the Idaho fescue plants, these sites should be seeded after fire • Community 1.4, and any site with low cover of bluebunch wheatgrass, and any site with moderate to heavy cover of cheatgrass should be seeded after fire.
Submodel
Description
State 2 represents invasion by annual grasses and is the gradation between Reference state and state 3. State 2 is shrub steppe with the inclusion of invasive annual grasses such as cheatgrass. The loss if soil biological crusts and annual grass seed blowing onto the site annually contributes to the annual grass invasion. All the native functional, structural groups are still represented by one or more species. This state can occur with or without bitterbrush. For communities 2.1, 2.2, and 2.3 the amount of cheatgrass is minor. Cheatgrass is more prominent in community 2.4. Once a community has been invaded by cheatgrass the chance of going back to State 1 is small. This state can occur with or without bitterbrush. Community Phases for state 2: Same four communities as for Reference state. Dominate State 2 Species: Bitterbrush, bluebunch wheatgrass Pathways within State 2: Same as for Reference state
Submodel
Description
State 3 represents communities dominated by invasive annual species and has crossed a biological threshold. Virtually all the native functional, structural groups are missing. This state can occur with or without shrubs. Important species can include cheatgrass, Japanese brome, medusahead, ventenata, mustard, prickly lettuce and diffuse knapweed. Community Phases for state 3: 3.1 Shrub – Annual Grass Bitterbrush – Annual bromes 3.2 Annual Grass Annual bromes Dominate state 3 Species: Annual grasses such as cheatgrass, with or without shrubs The main species can include Japanese brome, medusahead, ventenata, mustard, prickly lettuce and diffuse knapweed. This state can occur with or without shrubs.
Submodel
Description
State 4 represents a site that has been seeded to desirable grasses such as Secar Snake River wheatgrass, Sherman big bluegrass, crested wheatgrass or intermediate wheatgrass. The communities in State 4 are stable as long as they maintain 0.8 plant per square feet or greater of the desired grasses Dominate Species for State 4: Desirable seeded grass species with or without shrubs and legumes Community Phases for State 4: 4.1 Seeded Grass 4.2 Shrub – Seeded Grass
Submodel
Mechanism
Result: shift from Reference State to State 2 with a few annual grasses.
Ecological process: annual grass seeds blow onto the site awaiting an opportunity to colonize. Loss of soil biological crusts also contributes to the invasion be annual grasses.
Primary trigger: soil disturbances from rodent or badger activity provide great opportunity for invasive annual species. Fire, drought and grazing pressure can create holes in the plant community. Indicators: A few annual grasses have colonized the site.
Mechanism
Result: shift from State 2 with a few annuals to State 3 which is dominated by annual grasses. This transition occurs once the cover of bluebunch wheatgrass declines to less than 10% and invasive species cover is greater than 40%. Primary trigger: Grazing pressure (heavy grazing, season long grazing or frequent late spring grazing) causes low vigor and reduced cover of bluebunch wheatgrass. Initially both needleandthread and the annual grasses increase. As the grazing pressure continues, needleandthread will also decrease. Secondary trigger: repeated fire which is not a common occurrence in MLRA 8. Ecological process: With consistent defoliation pressures bluebunch wheatgrass and needleandthread experience poor plant vigor to such a degree that grass roots begin to die. So, bunchgrasses have shrinking crowns and some mortality. This gives invasive annual grasses opportunity to expand its cover to a position of dominance. Indicators: Significant decline in vigor and cover of one or more of the dominant reference state species – bluebunch wheatgrass, bitterbrush. Increasing cover of annual grasses. Increasing canopy gaps between bluebunch wheatgrass plants.
Mechanism
Equipment limitations from surface rock and rock in the profile will cause issues and some treatment options may not be feasible on some sites. R3A Result: shift from State 3 dominated by annual grasses to State 4 seeded grasses. This restoration transition is not likely to occur without significant time and inputs for weed control, seedbed preparation, seeding operation and post-seeding management & weed control. Two years of weed control, 1-2 years of deferment post-seeding, and proper grazing management afterward.
Mechanism
Result: Shift from State 3 back to State 2. This restoration transition does not occur without a significant commitment of time & resource inputs to restore ecological processes, native bunchgrasses, bitterbrush and native forb species. Attention needs to be paid to each step of the process: weed control, seedbed preparation, seeding and planting operations and post-seeding management.
Shifting from State 3 to State 4: If the goal is to restore back to a native plant community, State 3 must first be shifted to State 4. It will take two years or longer to kill annual species and to exhaust the seedbank of invasive species. Site will then need to be seeded to perennial species such as crested wheatgrass to restore soil properties before native species can survive and thrive on site. The seeded species rebuild some of the basic soil properties including increased soil organic matter, increased soil moisture, and likely would also require the soil’s pore spaces, bulk density and soil microorganisms to return before the native species that used to survive in this ecological site can return. The site would also need several years of no significant fires and proper grazing management as well. See narrative for R3A transition above.
Shifting from State 4 to State 2: This assumes that the shift from State 3 to State 4 has been successful. Introduced grasses must be killed before seeding native species. The seeding of native species should occur in two steps: (1) a seeding of native bunchgrasses so that broadleaf weeds may be controlled, (2) a re-introduction of sagebrush and native forbs. The site would also need several years of no significant fires and proper grazing management as well to ensure plant establishment and vigor. Shrubs and native forbs should not be planted until broadleaf weeds have been controlled.
Mechanism
Transition from State 4 seeded grass to State 3 annual grasses. This transition occurs when the desirable seeded grasses become minor to the dominant annual grasses.
Primary trigger: grazing pressure on the seeded grasses reduce the vigor and density of key bunchgrass species. Ecological process: the unraveling of the seeded grass community begins with weakened vigor and less cover of the seeded grasses. Invasive annual grasses colonize the site and become more and more common with the loss of each bunchgrass.
Ecological process: consistent defoliation pressure causes weakened vigor, roots dying and less cover for the seeded grasses. Invasive annual grasses colonize the site and become more and more common with the loss of each bunchgrass plant. Indicators: shrinking crowns and mortality of desirable species, increasing caps gaps between seeded plants, increasing cover by annual grasses.
Model keys
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