Calcareous Loam
Scenario model
Current ecosystem state
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Management practices/drivers
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- Transition T1 More details
- Restoration pathway R1 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 a native community with no invasive or exotic weed species. Calcareous Loam ecological site has low species diversity with winterfat, Sandberg bluegrass and not much else.
Reference State Community Phases:
Reference Community Winterfat – Sandberg bluegrass
Dominate Reference State Species:
Winterfat, Sandberg bluegrass
At-risk Communities:
• Any Calcareous Loam community is at risk when Sandberg bluegrass cover is declining and cheatgrass or broadleaf weeds have colonized the site. The seed source of invasive species is nearby and blowing onto most sites annually
Description
State 2 Narrative:
State 2 represents plant communities that have crossed a threshold to an altered state. Invasive species have colonized the site and have become dominant.
Community Phases for State 2:
Invasive annual grass / broadleaf weeds – half shrub – shrub
Dominate State 2 Species:
Annual grasses and broadleaf weeds dominate the understory. Winterfat persists in the overstory.
Mechanism
Transitions from State to State
T1 Result: transition from Reference State to State 2 Annual Invasive Species.
Primary Trigger: under heavy grazing pressure winterfat plants become hedged but persist remarkably well. Then Sandberg bluegrass becomes heavily grazed but does not fare well and invasive species invade.
Secondary Trigger: high moisture year that causes a micro-flush of cheatgrass
Ecological process: with consistent defoliation pressure winterfat plants become hedged while Sandberg bluegrass plants decline with poor vigor, shrinking crowns and mortality.
Colonization by invasive species: a high moisture year that causes a micro-flush of cheatgrass and broadleaf weeds and is the principle means of colonization. Most sites in the Reference State receive invasive weed seed annually. This seed is waiting for enough moisture to germinate and to 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 invasive species. In normal and dry years invasive species are all but nonexistent.
Expansion of invasive species: as Sandberg bluegrass continue to decline invasive species become co-dominant and then dominant. It is the declining Sandberg bluegrass cover that ensures invasive species will colonize successfully and expand.
Indicators: The occurrence of invasive species on sites where they had been absent. Declining cover and increasing distance between Sandberg bluegrass plants.
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.