Sands
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
- Transition T1 More details
- Restoration pathway R1 More details
- Restoration pathway T2 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 Narrative:
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.
The Reference Community 1.1 is native grass - shrub dominated by needle and thread, Indian ricegrass, sagebrush, or bitterbrush. Native forbs are also present.
Fire eliminates the shrubs, so Community 1.2 is a grassland community. Community 1.3 is heavy shrub-grass.
Reference State Community Phases:
1.1 Reference Sagebrush/bitterbrush – needle and thread – Indian ricegrass
At-risk Communities:
• Community 1.3 is most at risk of transitioning to State 3
• All communities are at risk when native bunchgrass density falls to 10 percent and cheatgrass has colonized the site.
Submodel
Description
State 2 Narrative:
State 2 represents sites dominated by invasive annual species and have crossed a biological threshold. As Reference State begins to unravel the dominant bunchgrasses decline while invasive grasses become more and more prominent. Virtually all the native functional, structural groups are missing in State 2.
Community Phases for State 2:
2.1 Sagebrush – Annual Grass
2.2 Rabbitbrush – Annual Grass
Dominate State 2 Species:
Annual grasses such as cheatgrass, sagebrush and rabbitbrush. Other species can include mustard, prickly lettuce, Russian thistle and diffuse knapweed.
Pathways within State 2
2.1a Result: shift from sagebrush-cheatgrass community to rabbitbrush-cheatgrass community.
Primary Trigger: moderate severity fire
Ecological Process: fire sensitive shrubs (sagebrush and bitterbrush) are killed by the fire. Rabbitbrush expands via sprouting and new seedlings while cheatgrass expands by seedlings.
Description
State 3 Narrative:
State 3 represents a site that has been seeded to grasses such as Siberian wheatgrass, crested wheatgrass and Secar Snake River wheatgrass. State 3 is stable if 0.8 plant per square foot or greater of the desired bunchgrasses is maintained.
Dominate Species for State 3:
Desirable seeded grass species with or without legumes
Community Phases for State 4:
3.1 Seeded Grass
3.2 Shrub Grass
Pathways within State 3
3.1a Result: shift from seeded grass community to shrub-seeded grass community.
Primary Trigger: grazing pressure to desirable seeded grasses
Ecological Process: consistent defoliation pressure to seeded grasses results in poor vigor, shrinking crowns and plant mortality. Shrubs increase to occupy the niche space vacated by the seeded grasses.
Mechanism
T1 Result: shift from Reference State to State 2 which is dominated by annuals and shrubs. This transition occurs once the cover of needle and thread and Indian ricegrass declines to less than 10 percent and invasive species cover is greater than 40 percent.
Primary Trigger: soil disturbances (rodents, badgers) create openings or opportunities in the community or a high moisture year causes a micro-burst of cheatgrass and is the principle means of colonization.
Secondary Trigger: Repeated fire does the same thing. In Washington, chronic season-long grazing caused more acres of State 2 than repeated fire. Repeated fire is a much more common event in south Central Washington.
Ecological process.
1. Colonization: annually cheatgrass seed blows onto most Reference State sites. This seed is waiting for opportunity to germinate and compete with the native species for space, light and moisture. When the right year happens even pristine communities in the Reference State are susceptible to colonization by cheatgrass.
2. Dominance by annuals: the unraveling of the native plant community begins with weakened vigor and less cover of the dominant bunchgrasses, or the sudden loss of a major species such as Indian ricegrass. The invasive annual grasses in make a dramatic increase to dominate the community.
Consistent defoliation pressure causes low vigor and reduced cover of Indian ricegrass and needle and thread. Initially needle and thread and the annual grasses increase while Indian ricegrass declines. As the defoliation pressure continues, needle and thread also decreases allowing the annual grasses to become dominate. Grazing pressure is defined as heavy grazing, season long grazing or frequent late spring grazing.
Indicators: The occurrence of annual grasses on sites where they had been absent. Decreasing vigor and cover of needle and thread and Indian ricegrass and increasing cover of invasive annual species. Increasing distance between perennial species. Decreasing soil organic matter, soil water retention, limited water infiltration and percolation in the soil profile.
Mechanism
Recovery
R1 Result: shift from State 2 dominated by annual grasses to State 3 seeded 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 requires 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 inch is desired). Proper grazing management is essential to maintain the stand post-seeding. Siberian wheatgrass, crested wheatgrass, Secar Snake River wheatgrass, thickspike wheatgrass and Sherman big bluegrass may be seeded.
The actual transition occurs when the seeded species have successfully established and are outcompeting the annual species for cover and dominance of resources.
Mechanism
T2 Result: Transition from State 3 seeded grass to State 2 annual grasses. This transition occurs when the desirable seeded grasses become minor to the dominant annual grasses.
Ecological process: consistent defoliation pressure to the seeded grasses results in poor vigor, shrinking crowns and plant mortality. At the seeded grass community unravels, invasive annual grasses colonize the site and become more and more common with the loss of each bunchgrass.
Primary trigger: grazing pressure on the seeded grasses reduce the vigor and density of key bunchgrass species.
Indicators: shrinking crowns and mortality of desirable species, increasing caps gaps between perennial species, increasing cover by annual grasses.
Model keys
Briefcase
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Ecological site groups
Major Land Resource Areas
The Ecosystem Dynamics Interpretive Tool is an information system framework developed by the USDA-ARS Jornada Experimental Range, USDA Natural Resources Conservation Service, and New Mexico State University.