Sandy Loam
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
- Transition 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 dominated by Wyoming sagebrush, needle and thread and bluebunch wheatgrass. Native forbs are also present.
Reference State Community Phases:
1.1 Reference Wyoming sagebrush – Needle and thread / Indian ricegrass
Dominate Reference State Species: Wyoming sagebrush, needle and thread, bluebunch wheatgrass
At-risk Communities:
All communities in the reference state are at risk on invasion by cheatgrass. Cheatgrass seeds blow onto most sites annually.
Community 1.3 Heavy Sagebrush is more at risk of shifting into State 2 than the other Reference State communities.
Submodel
Description
State 2 Narrative:
State 2 represents sites dominated by invasive annual species and has crossed a biological threshold. As Reference State 1 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:
2.2 Annual Grass: Cheatgrass
Dominate State 2 Species:
Annual grasses such as cheatgrass, the main species can include mustard, Russian thistle, prickly lettuce and diffuse knapweed.
Pathways within State 2
2.1a Result: shift from sagebrush-cheatgrass community to cheatgrass community
Primary trigger: moderate severity fire kills sagebrush.
Ecological process: death of sagebrush releases resources and niche space. Cheatgrass expands cover to the point of dominance.
Description
State 3 Narrative:
State 3 represents a site that has been seeded to desirable grasses such as needle and thread, Indian ricegrass, Secar Snake River wheatgrass, Sherman big bluegrass, or Siberian wheatgrass. State 4 is stable if 0.8 plants 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 3:
3.1 Seeded Grass
Submodel
Mechanism
T1 Result: transition from Reference State to State 2 which is dominated by annual grasses. This transition occurs once the cover of needle and thread and bluebunch wheatgrass decline to less than 10 percent and invasive species cover is greater than 40 percent.
Primary Trigger: heavy grazing pressure (heavy grazing intensity, season long grazing and frequent late spring grazing) results in declining bunchgrasses and invasion by invasive annual grasses.
Ecological process: consistent defoliation pressure to bluebunch wheatgrass and other native bunchgrasses results in poor vigor, shrinking crowns and mortality. The unraveling of the native plant community begins with a decline in bluebunch wheatgrass, while both needle and thread and sagebrush increase. As the grazing pressure continues, needle and thread will also decrease allowing the annual grasses to colonize and then become dominate.
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. 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
Indicators: The occurrence of annual grasses on sites where there has been none. Decreasing vigor and cover of needle and thread and bluebunch wheatgrass 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 desirable 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.
Needle and thread, Indian ricegrass, Secar Snake River wheatgrass, thickspike wheatgrass, Sherman big bluegrass, Sandberg bluegrass, and intermediate wheatgrass are typical species seeded on Sandy Loam 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
T2 Result: Transition from State 3 seeded grasses to State 2 annual grasses. This transition occurs when the desirable seeded grasses become minor to the dominant annual grasses. This shift can happen with or without sagebrush.
Primary Trigger: grazing pressure on the seeded grasses reduce the vigor and density of key bunchgrass species.
Ecological process: consistent defoliation pressure to desirable seeded grasses results in poor vigor, shrinking crowns and plant mortality. As the unraveling of the seeded grass community continues invasive annual grasses colonize the site and become more and more common with the loss of each bunchgrass.
Indicators: shrinking crowns and mortality of desirable species, increasing caps gaps between perennial species, increasing cover by annual grasses.
Model keys
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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.