Natural Resources
Conservation Service
Scenario model
Current ecosystem state
Select a state
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 reference state has three general community phases; a perennial grass dominant phase, a shrub-grass dominant phase and a shrub dominant phase. State dynamics are maintained by interactions between climatic patterns and disturbance regimes. 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. Plant community phase changes are primarily driven by fire, periodic drought and/or insect or disease attack.
Submodel
State 2
Current Potential
Current Potential
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) and has the same three general community phases. Ecological function 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 non-natives high seed output, persistent seed bank, rapid growth rate, ability to cross pollinate and adaptations for seed dispersal.
Submodel
State 3
Shrub State
Shrub State
Description
This state has two general community phases: a shrub phase with an annual non-native understory and a non-native annual dominated phase. This state has crossed a biotic threshold and site processes (soil hydrology, nutrient cycling, and energy capture) are being controlled by the shrub component of the plant community. Perennial bunchgrasses may or may not be present in trace amounts. The herbaceous understory is dominated by annual non-native species such as cheatgrass and mustards. Resiliency has declined and further degradation from fire facilitates a cheatgrass and sprouting shrub plant community. The fire return interval has shortened due to the dominance of cheatgrass in the understory and is a driver in site dynamics. Sagebrush may be eliminated by continued fire. Spiny hopsage and ephedra may resprout if grazing is controlled and drought does not occur following fire. Negative feedbacks enhance ecosystem resilience and contribute to stability of this state. These include the persistent seedbank and competitive ability of cheatgrass.
Submodel
State 4
Annual State
Annual State
Description
This state has crossed both a biotic and abiotic threshold. Annual invasive weeds, primarily cheatgrass and mustard, dominate the plant community. Sprouting shrubs may be present in trace amounts; sagebrush is missing. Ecological processes are controlled by the annual weed 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.
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. Non-native invasive 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: Inadequate rest and recovery from winter and spring defoliation and/or prolonged drought. Slow variables: long term decrease in grass density and reduced native species (shrub and grass) recruitment rates. Increased reproduction of non-native species. Threshold: loss of deep-rooted perennial bunchgrasses changes nutrient cycling and nutrient redistribution; thus reducing soil organic matter.
Mechanism
Trigger: Multiple stand replacing fires eliminates sagebrush and severely damages spiny hopsage. Typically occurs in the hot season. Slow variables: Increased reproduction and cover of non-native invasive annuals. Threshold: Loss of deep-rooted perennial bunchgrasses reduces infiltration and increases runoff; this leads to reduced soil organic matter and soil moisture. The natural fire regime is also modified (changes in intensity, size and spatial variability of fires).
Mechanism
Trigger: Multiple fires within a 10 to 20 year timeframe Slow Variables: Increased reproduction, cover and density of non-native annuals Threshold: Modified fire regime (changes in frequency, intensity, size and spatial variability of fire). Changes in plant community composition and spatial variability of vegetation (loss of perennial bunchgrasses and sagebrush).
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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