Overflow (Ov) LRU 01 Subset B
Scenario model
Current ecosystem state
Select a state
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
Select a state
Description
The Reference State of this ecological site consists of two (2) potential plant communities: the Decreaser Bunchgrass Community and the At Risk Community. These are described below but are generally characterized by a mid-statured, cool-season grass community with limited shrub production. Community 1.1 is dominated by basin wildrye, rough fescue, and green needlegrass and is considered the reference, while Community 1.2 has a codominance of decreaser and increaser bunchgrasses with an increase in big sagebrush. These communities may meld into each other due to the varying conditions that occur in Southwest Montana, particularly during dry cycles.
Submodel
Description
State 2, Rhizomatous State, has been altered by long-term unmanaged, heavy grazing. In this State, drought conditions may speed the departure from reference.
Submodel
Description
Heavy disturbance has allowed for bare ground and invasive species to dominate the site. Native plants may persist, but dominance has been transferred to non-native grasses and forbs. Hydrologic function is nearly lost as runoff increases. Site stability is greatly reduced from the Reference State due to reduced soil organic matter and a subsequent change in soil microbiota.
This is a terminal state, and restoration to reference cannot be obtained without great expenditure of energy and finances. The resulting community of attempted restoration will not have the same hydrology and functional/structural groups expressed in Reference. Often, an attempted restoration will still contain invasive species at a level at which they will likely return to the Invaded State.
Submodel
Mechanism
The Reference State (1) transitions to the Rhizomatous State (2) if tall and mid-statured bunchgrasses decrease to below 20 percent or if bare ground cover increases beyond 10 percent. The driver for this transition is the loss of taller bunchgrasses, which creates open areas in the plant canopy with bare soil. Soil erosion reduces soil fertility, which drives transitions to the Altered State. There are several other key factors signaling the approach of transition T1A: increases in soil physical crusting, an increase in rhizomatous grasses, 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 trigger for this transition is improper grazing management and/or long-term drought, leading to a decrease in basin wildrye composition to less than 10 percent and a reduction in total plant canopy cover.
Mechanism
Rapid invasion of the Reference State is often a result of repeated heavy disturbance from non-managed grazing (often combined with prolonged drought), stressing native bunchgrasses. Seeds of non-native grasses and forbs readily germinated in the bare ground between bunchgrass culms.
Mechanism
The Rhizomatous State (2) has lost soil or vegetation attributes to the point that recovery to the Reference State (1) will require reclamation efforts such as soil rebuilding, intensive mechanical and cultural treatments, and/or revegetation (via seeding or sprig planting in the case of basin wildrye). Examples of mechanical treatment may be brush control, while cultural treatments may include prescribed grazing, targeted brush browsing, or prescribed burning. Low intensity prescribed fires to reduce competitive increaser plants as well as reduce the potential Kentucky bluegrass invasion. A low-intensity fire will also reduce big sagebrush densities. In areas with the potential for annual grass infestations, fire should be carefully planned or avoided. The drivers for this restoration pathway are reclamation efforts along with proper grazing management.
Mechanism
With continued disturbance, the Rhizomatous State can deteriorate, losing the majority of the native bunchgrasses as well as reducing the native rhizomatous grasses. Non-managed grazing is the driver of this transition. Limited impacts from prolonged drought may influence this transition as well. Disturbance-adapted non-native species compete for limited resources, reducing the vigor of native species. Bare ground between Kentucky bluegrass tillers significantly increases. This transition results in significantly reduced site stability as well as an increased risk of runoff. This combination may be expressed in headcutting during brief runoff events.
Mechanism
Restoration of the Invaded State (3) to the Reference State (1) requires substantial energy input. The drivers for the restoration pathway are the removal of invasive species, restoration of native bunchgrass species, persistent management of invasive species, and proper grazing management. Without continued control, invasive species are likely to return (probably rapidly) due to the presence of seeds and/or other viable material in the soil and management-related practices that increase soil disturbance. If invaded by conifer encroachment, treatment depends on the condition of the rangeland.
Sites invaded by Kentucky bluegrass and smooth brome (Bromus inermus) have been successfully restored by prescribed fire and herbicide treatments (Matt A. Bahm et al. 2011). Prescribed fire of Kentucky bluegrass invaded sites has shown to temporarily increase runoff; however, one year post-fire treatment of Kentucky bluegrass, infiltration rates increased (Gerhard 2019).
Sites that have transitioned from the Rhizomatous State (2) to the Invaded State (3) may be severely lacking in soil and vegetative properties that will allow for restoration to the Reference State. Hydrologic function damage may be irreversible, especially with accelerated gully erosion.
Mechanism
If invasive species are removed before remnant populations of bunchgrass are drastically reduced, the Invaded State (3) can revert to the Rhizomatous state. The driver for the reclamation pathway is weed management without reseeding. Continued Integrated Pest Management (IPM) will be required as many of the invasive species that can occupy the Invaded State have extended dormant seed life. The trigger is invasive species control.
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.