LOAMY 8-10 P.Z.
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
- Restoration pathway R3A More details
- Transition T3A More details
- Transition T3B More details
- Transition T4A More details
- Transition T5A 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 a representative of the natural range of variability under pristine conditions. The reference state has three general community phases: a shrub-grass dominant phase, a perennial 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
Description
State 2 This state is similar to the Reference State (1) and the same three community phases occur. Ecological function has not changed, however the resiliency of the state has been reduced by the presence of non-native invasive species (5-15% by weight). Low frequency and low intensity disturbances favor the grass-dominant and grass-shrub mixture phases but the presence of non-natives is favored if frequency and severity of disturbances change from historic conditions. Prescribed grazing and infrequent fire (50-100 year return interval) maintain state dynamics. Prescribed grazing and/or release from drought may reverse declines in Thurber’s needlegrass and Indian ricegrass production.
Submodel
Description
State 3 has two community phases. One phase is a dense overstory of decadent Wyoming big sagebrush and an understory of Sandberg's bluegrass, a shallow-rooted cool season perennial bunchgrass. The second community phase is dominated by Sandberg’s bluegrass with non-native annuals in the plant community. A trace of deep-rooted perennial bunchgrasses remains in the plant community. Non-native annual grasses and forbs are abundant in the understory. A biotic threshold has been crossed and site resiliency has been reduced with the loss of the deep rooted perennial bunchgrasses. Feedbacks contributing to the stability of this state include the loss of structural and functional groups (deep-rooted perennial bunchgrasses and shrub seedlings), resulting in decreased herbaceous production and reduced organic matter inputs. Changes in infiltration and runoff rates contribute to reduced soil moisture availability thereby reducing reproductive potential of native species.
Description
State 4 has two community phases. One phase is dominated by non-native annual species, primarily cheatgrass, halogeton, Russian thistle, fiddleneck, and annual mustards. Sandberg's bluegrass and squirreltail may also occur. The second community phase is dominated by fire tolerant shrubs and non-native annuals. An abiotic threshold has been crossed and state dynamics are now driven by fire and time. The length of time between fires creates two potential community phases with broom snakeweed and rabbitbrush increasing with fire return intervals >10 years. This alternative stable state is persistent due to strong feedbacks, including presence of non-natives; competition from non-native species for soil moisture and nutrients prevent germination and establishment of native species. Fine-fuel loading supports a modified fire regime too narrow for the successful establishment of Wyoming big sagebrush and favors an increase of non-native invasive annuals. Biogeochemical cycling is altered by 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.
Description
The seeded state that has three community phases; a grass dominated phase, a shrub-grass co-dominated phase and a shrub phase. The seeded species may be native or non-native. Annual non-native species may also be present. Following wildfire, range plantings help to stabilize the soil surface, reduce erosion and provide competition for non-native annuals. Seeded species may include native and non-native species. Annual non-natives may be present. Typically there is an overall lack of native perennial forbs. However, some seeded forbs, like western yarrow (Achillea millefolium), may do quite well. Feedbacks contributing to the stability of this state include competitive ability and vigor of seed species. Seeded perennial grasses reduce the availability of critical resources to non-native annuals, reducing fire frequency.
Mechanism
Trigger: This transition is caused by the introduction of non-native annual weeds; such as cheatgrass, Russian thistle (Salsola iberica), medusahead, or stork’s bill (Erodium spp.) dominate the understory.
Slow variables: Over time the annual non-native plants will increase within the community decreasing organic matter inputs from deep-rooted perennial bunchgrasses resulting in reductions in soil water availability for perennial bunchgrasses.
Threshold: Any amount of introduced non-native species causes an immediate decrease in the resilience of the site. 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: Inappropriate, long-term grazing of perennial bunchgrasses during growing season would favor shrubs and initiate transition to Community Phase 3.1. Fire would cause a transition to Community Phase 3.2.
Slow variables: Long term decrease in deep-rooted perennial grass density resulting in a decrease in organic matter inputs and subsequent soil water decline.
Threshold: Loss of deep-rooted perennial bunchgrasses changes spatial and temporal nutrient cycling and redistribution, and reduces soil organic matter.
Mechanism
Trigger: Fire or a failed range seeding leads to plant community phase 4.1. Inappropriate grazing management that favors shrubs in the presence of non-native annual species leads to community phase 4.2.
Slow variables: Increased production and cover of non-native annual species.
Threshold: Cheatgrass or other non-native annuals dominate understory.
Mechanism
Trigger: Fire or inappropriate grazing management can eliminate the bottlebrush squirreltail understory and transition to community phase 4.1 or 4.2.
Slow variable: Increased seed production and cover of annual non-native species.
Threshold: Increased, continuous fine fuels modify the fire regime by changing intensity, size and spatial variability of fires. Changes in plant community composition and spatial variability of vegetation due to the loss of perennial bunchgrasses and sagebrush truncate energy capture and impact the nutrient cycling and distribution.
Model keys
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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.