Natural Resources
Conservation Service
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
- Transition T1A More details
- Transition T2A More details
- Transition T2B 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
Select a state
Description
The reference state is representative of the natural range of variability under pristine conditions. The visual aspect of the plant community is dominated by an evergreen shrub community. State dynamics are maintained by interactions between climatic patterns and disturbance regimes. Plant community phase changes are primarily driven by fire, periodic drought and insect or disease attack.
Submodel
Description
This state is characterized by the presence of non-native invasive species in the understory. This state is similar to the Reference State (1). Ecological function (soil hydrology, nutrient cycling, energy capture) has not changed, however the resiliency of the state has been reduced by the presence of invasive weeds. Prescribed grazing and infrequent fire maintains state dynamics. These non-natives are highly flammable and can promote wildfire where fires historically have been infrequent. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These include the presence of all structural and functional groups, low fine fuel loads and retention of organic matter and nutrients. Positive feedbacks decrease ecosystem resilience and stability of the state. These include cheatgrass’s high seed output, persistent seed bank, rapid growth rate, ability to cross pollinate and adaptations for seed dispersal.
Submodel
Description
This state is characterized by a by sparse overstory of shrubs and an understory of non-native annuals in the plant community primarily; cheatgrass, mustard, halogeton and Russian thistle. Sprouting shrubs are present in trace amounts. Negative feedbacks contributing to the stability of this state include the persistence of non-natives and competition from non-natives for soil moisture and nutrients preventing recruitment of native species. Fine fuels provided by non-native annuals support a fire regime too frequent for the successful establishment of woody native perennials and favor an increase in non-native annuals. Fire occurs often enough in this state to preclude the establishment of rabbitbrush, fourwing saltbush or dominance of sprouting shrubs. Biogeochemical cycling is altered by the dominance of cheatgrass modifying the soil environment. Cheatgrass monocultures have low VAM fungal populations, increasing the difficulty of reestablishing sagebrush and native bunchgrasses that require these mycorrhizae.
Submodel
Description
This state is characterized by active soil movement. Annual non-native species, including cheatgrass, mustards and Russian thistle, dominate the plant community. Sprouting shrubs may be present in trace amounts. Ecological processes are controlled by the non-native annual community during the spring growing season and by the physical process of wind movement of soil after the annual plant cover has senesced. In extremely degraded sites wind erosion of soil may progress to dune formation or flattening (depending on landscape position) and near elimination of the annual plant community. Negative feedbacks contributing to the stability of this state include the persistence of non-natives and competition from non-natives for soil moisture and nutrients prevent recruitment of native species. Fine fuels provided by non-native annuals support a fire regime too frequent for the successful establishment of sagebrush and favor an increase in non-native invasive annuals.
Submodel
Mechanism
Trigger: introduction of non-native annual species. Slow variables: Changes in the kinds of animals and their grazing patterns, drought and/or changes in fire history that altered recruitment rates of native species. Threshold: Reduction in deep-rooted herbaceous understory reduces productivity, changes nutrient cycling and soil stability. Annual non-native species cannot be easily removed from the system and have the potential to significantly alter disturbance regimes from their historic range of variation.
Mechanism
Trigger: Multiple stand replacing fires to severely damage spiny hopsage and other fire tolerant shrubs. Typically occurs in the hot season. Slow variables: Increased reproduction and cover of non-native invasive annuals. Threshold: Loss of deep-rooted perennial bunchgrasses reduced infiltration and increases runoff; this leads to reduced soil organic matter and soil moisture. Modified fire regime (changes in intensity, size and spatial variability of fires).
Mechanism
Trigger: Inadequate rest and recovery from growing season defoliation and/or prolonged drought. Slow variables: Long term decrease in grass density and reduced native species (shrub and grass) recruitment rates. Threshold: Loss of deep-rooted perennial bunchgrasses changes nutrient cycling and nutrient redistribution; thus reducing soil organic matter.
Mechanism
Trigger: Frequent, repeated stand replacing fires Slow Variables: Loss of perennial bunchgrasses and native shrubs, increased reproduction, cover and density of non-native annuals and increased bare ground Threshold: Modified fire regime (changes in frequency, intensity, size and spatial variability of fire). Permanent changes in plant community composition and spatial variability of vegetation (loss of perennial bunchgrasses and shrubs).
Model keys
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Ecological sites
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.
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