Loamy Bottom
Scenario model
Current ecosystem state
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Management practices/drivers
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- Transition T1A More details
- Restoration pathway R2A More details
- Restoration pathway R2B More details
- Transition T3A 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 sagebrush steppe with none to minor amounts of invasive or exotic weed species. All the functional, structural groups have one or more native species. Refer to the Ecological Dynamics section where the variations of Loamy Bottom are discussed. The Reference State discussion below is for basin wildrye – sagebrush, the largest of the variations. Reference State Community Phases: 1.1 Basin Wildrye and Sagebrush, 1.2 Basin Wildrye, and 1.3 Heavy Sagebrush and Basin Wildrye
Dominant Reference State Species: Basin wildrye, Basin and/or Wyoming big sagebrush At-risk Communities: • All communities in the reference state are at risk of invasion by exotic species. Annual or biennial weeds and annual grass seeds blow onto most sites annually • Community Phase 1.3, the heavy sagebrush community, has the highest risk of moving to State 2 which is dominated by invasive weeds or annual grasses • Any Loamy Bottom community with high sagebrush cover and low cover of basin wildrye will also have invasive weeds, and thus, no longer be in the Reference State • To seed or not to seed is the question after a fire. Community 1.3 should be seeded to basin wildrye to minimize weed infestation. Any site with low cover of basin wildrye and any site with low to moderate cover of weeds should be seeded after a fire. State 2 and Community 3.2 should also be seeded
Submodel
Description
State 2 represents invasive species communities that have crossed a biological threshold. Virtually all the native functional, structural groups are missing. This state can occur with or without sagebrush. Community Phases for State 2: Can have several variations: 1. Invasive annual or biennial weeds (mustard, prickly lettuce, perennial pepperweed) 1. Invasive annual grasses (annual bromes, medusahead) 2. Sagebrush with invasive weeds or annual grasses Dominate State 2 Species: Invasive weeds: mustard, prickly lettuce, perennial pepperweed, knapweeds Invasive annual grasses: annual bromes, cheatgrass, medusahead, ventenata with sagebrush and rabbitbrush
Submodel
Description
State 3 represents a site that has been seeded to desirable grasses such as basin wildrye or intermediate wheatgrass. Community 3.1 remains stable with 0.8 plants per square foot or greater of mid-sized bunchgrasses or with a full stand of basin wildrye. Community Phases for State 3: 3.1 Seeded Grasses 3.2 Shrub, Invasive Weeds, and Seeded Grasses
Submodel
Mechanism
Result: Shift from Reference State (native shrub steppe with no invasive species) to State 2 which is dominated by invasive weeds or annual grasses. The pathway from State 1 to State 2 occurs as Community 1.3 declines until it crosses the biological threshold. This transition occurs once the cover of basin wildrye drops to 5% and invasive species cover is at least 40%. Primary Trigger: grazing pressure (heavy grazing, season-long grazing, or late spring grazing) to basin wildrye. Secondary Trigger: Frequent fires or one severe fire can have the same effect. Also, several years of drought can put the basin wildrye in decline. Ecological process: with consistent defoliation pressure basin wildrye and other bunchgrass have low vigor, shrinking crowns and mortality. Weed seeds from invasive species blow onto the site or are carried in with runoff water. On most sites weed seeds are waiting for an opportunity to colonize. As basin wildrye cover declines invasive species increase accordingly. Over time the invasive species expand to a position of dominance. Indicators: Decreasing cover of basin wildrye and increasing cover of invasive species. Increasing canopy gaps between native perennial species. Decreasing soil organic matter, soil water retention, limited water infiltration and percolation in the soil profile.
Mechanism
Result: Shift from invasive species in State 2 back to Reference State. This restoration transition does not occur without a significant commitment of time & resource inputs to restore ecological processes, native bunchgrasses, sagebrush and native forb species. TWO OPTIONS: Option#1: Step 1 seed to introduced grasses; Step 2 seed to native species Step 1 shifting from State 2 to State 3: It will take two years or longer to kill annual species and to exhaust the seedbank of invasive weed seed. Site will then need to be seeded to introduced 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, improved pore spaces and increased soil moisture within the soil profile. The site would also need several years of no significant fires and proper grazing management as well. See narrative for R1 recovery above. Step 2 shifting from State 3 to State 1: This assumes that the shift from State 2 to State 3 has been successful. Introduced grasses and any remaining weeds must be killed while maintaining soil structure to ensure a proper seedbed (cloddy, a little rough and trashy to provide safe sites for the seed). A pulverized dust mulch must be avoided at all costs. The seeding of native species could occur in two steps: (1) first year, use a grass seed mix to duplicate the Reference Community (mostly basin wildrye with other native bunchgrasses) so that broadleaf weeds may be controlled, and (2) second year re-introduce sagebrush and native forbs. Plugs may be used for sagebrush and native forbs rather than seed. Post-seeding the site would also need several years with no significant fires and proper grazing management as well to ensure plant establishment and vigor. Option #2: seed directly to native species Take two years or more to kill weeds and to exhaust the weed seedbank while maintaining soil structure. As in Option 1 above, the seeding of native species could occur in two steps: (1) first year, use a grass seed mix to duplicate the Reference Community (mostly basin wildrye with other native bunchgrasses) so that broadleaf weeds may be controlled, and (2) second year re-introduce sagebrush and native forbs. Plugs may be used for sagebrush and native forbs rather than seed. Post-seeding the site would also need several years with no significant fires and proper grazing management as well to ensure plant establishment and vigor.
Mechanism
Transition from State 2 (a community dominated by invasive annual species) to State 3 seeded grasses (basin wildrye or to introduced grasses). This restoration transition does not occur without significant time and inputs to control weeds, prepare a seedbed, seed desirable species, and post-seeding weed control and management. This can require a commitment of two years or more for weed control. Care must be taken to maintain soil structure so that the seedbed has many safe-sites for the seed. Seed placement must be managed to achieve seed-soil contact at very shallow depth (about 1/8-1/4 inch is desired). Proper grazing management is essential to maintain the stand post-seeding. Basin wildrye and intermediate wheatgrass are highly adapted to the Loamy Bottom ecological site. The actual transition occurs when the seeded species have successfully established and are outcompeting the annual species for cover and dominance of resources.
Mechanism
Result: Shift from State 3 (seeded grasses) to State 2 which dominated by invasive weeds or annual grasses. Primary Trigger: grazing pressure (heavy grazing, season long grazing, or frequent late spring grazing) to seeded grasses. Secondary Trigger: Frequent fires or a severe fire that burn out plant crowns of native species and give competitive advantage to the invasive species. This transition occurs when chronic heavy grazing has removed too much of the perennial bunchgrass cover allowing invasive annual species to colonize the site. As this continues the competitive advantage goes to the exotic species which are opportunistic and take most of the site’s resources. Ecological process: with consistent defoliation pressure seeded grasses have low vigor, shrinking crowns and mortality. Weed seeds from invasive species blow onto the site or are carried in with runoff water. On most sites weed seeds are waiting for an opportunity to colonize. As the cover of seeded grass declines invasive species increase accordingly. Over time the invasive species expand to a position of dominance. Indicators: shrinking crowns and mortality of desirable species, increasing gaps between perennial species, and increasing cover by invasive annual species.
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