Shallow Droughty (Swdr) LRU 43A-A
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
- Transition T1A More details
- Transition T1B More details
- Restoration pathway R2A More details
- Transition T2A More details
- Restoration pathway R3A More details
- Restoration pathway R3B 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
This state is characterized by cool-season bunchgrasses and is represented by two communities that differ mainly in the percent composition of bluebunch wheatgrass and needleandthread (Hesperostipa comata). Shrubs and forbs are a minor component in this state.
Submodel
Description
This state is characterized by having < 10% bluebunch wheatgrass and < 50% canopy cover. It is represented by two communities that differ in the percent composition of needleandthread and/or Idaho fescue, production, and soil degradation. Production in this state is considerably lower than in the Taller Bunchgrass State (1). Some native plants tend to increase under prolonged drought and/or heavy grazing practices. A few of these species may include needleandthread, Sandberg bluegrass, western yarrow, scarlet globemallow, hairy goldenaster, and fringed sagewort.
Submodel
Mechanism
The Taller Bunchgrass State (1) transitions to the Altered Bunchgrass State (2) if plant canopy cover declines to < 50% and bluebunch wheatgrass decreases to below 10% by dry weight. The trigger for this transition is the loss of taller bunchgrasses, which creates open spots of bare soil. Soil erosion is accompanied by decreased soil fertility driving the transitions to the Altered Bunchgrass State (2). There are several key factors signaling the approach of transition T1A: increases in soil physical crusting, decreases in cover of cryptogamic crusts, decreases in soil surface aggregate stability, and/or evidence of erosion, including water flow patterns, development of plant pedestals, and litter movement. The driver for this transition is improper grazing management and/or long-term drought leading to a decrease in bluebunch wheatgrass composition to < 10%.
Mechanism
Regardless of grazing management, without some form of weed management (chemical, mechanical, or biological control), the Taller Bunchgrass State (1) can transition to the Invaded State (3) if aggressive invasive species, such as spotted knapweed and cheatgrass are introduced, even if the herbaceous component of the reference community is thriving. Healthy plant communities are most resilient to invasives. Long-term stress conditions for native species (e.g., overgrazing, drought, and fire) accelerate the process. If populations of invasive species reach critical levels, the site transitions to the Invaded State (3). The driver for this transition is the presence of aggressive invasive species.
Mechanism
The Altered Bunchgrass State (2) has lost soil or vegetation attributes to the point that recovery to the Taller Bunchgrass State (1) will require reclamation efforts such as soil rebuilding, intensive mechanical treatments, and/or revegetation. The drivers for this restoration pathway are reclamation efforts and proper grazing management. The trigger is restoration efforts.
Mechanism
Invasive species can occupy the Altered Bunchgrass State (2) and drive it to the Invaded State (3). The Altered Bunchgrass State is at risk of this transition, if invasive propagules are present. The driver for this transition is the presence of critical population levels (> 25%) of invasive species. The trigger is the presence of propagules of invasive species.
Mechanism
Restoration of the Invaded State (3) to the Taller Bunchgrass State (1) requires substantial energy input. The drivers for this restoration pathway are removal of invasive species, restoration of native bunchgrass species, ongoing management of invasives, and proper grazing management. Without maintenance, invasive species are likely to return (probably rapidly) because of the presence of propagules in the soil and increase in soil disturbance. The drivers for this reclamation pathway are treatments to reduce or remove invasive/noxious species in combination with favorable growing conditions. The trigger is invasive species control.
Mechanism
If invasive species are removed without sufficient remnant populations of reference community species (particularly bluebunch wheatgrass), the Invaded State (3) is likely to return to the Altered Bunchgrass State (2) instead of the Taller Bunchgrass State (1). The driver for the reclamation pathway is weed management without reseeding. The trigger is invasive species control.
Model keys
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