Thin Claypan (TCp) LRU 01 Subset A
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
- Transition T1C More details
- Restoration pathway R2A More details
- Transition T2A More details
- Transition T2B More details
- Transition T3A More details
- Restoration pathway R4A More details
- Restoration pathway R4B More details
- Restoration pathway R4C 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 consists of two Plant Communities. The first is dominated by deep-rooted bunchgrasses, shrubs, and rhizomatous grasses. The second is co-dominated by bunchgrasses and rhizomatous grasses. These communities regularly interchange in response to varying climatic conditions and minor disturbances.
The Reference State exists where grazing by livestock and wildlife has historically been light to moderate and grazing events have been short. This reduces the opportunity for grazing regrowth and maintains.
Submodel
Description
This state is characterized by having less than 10 percent bluebunch wheatgrass by dry weight. It is represented by one (1) community. Production in this state can be similar to that in the Reference State (1). Some native plants tend to increase under prolonged drought and heavy grazing practices. A few of these species may include western wheatgrass, needle and thread, Sandberg bluegrass, scarlet globemallow, hairy goldenaster, and fringed sagewort.
Submodel
Description
Shortgrass-Shrub State lacks midstatured bunchgrasses. Western wheatgrass, blue grama, Sandberg bluegrass, and prairie Junegrass are dominant grasses. Increaser shrubs like broom snakeweed and prickly pear cactus are almost as productive as larger sagebrush shrubs. Most shrub species are heavily hedged. This state will be treated as a terminal one (e.g., restoration will likely be impossible or unsuccessful and require major energy inputs).
Submodel
Description
The Invaded State is identified as being in the exponential growth phase of invader abundance where control is a priority. Dominance (or relative dominance) of noxious or invasive species reduces species diversity, forage production, wildlife habitat, and site protection. A level of 10 percent invasive species composition by dry weight indicates that a substantial energy input will be required to create a shift to the grassland state (herbicide, mechanical treatment), even with a return to proper grazing management or favorable growing conditions. Prescriptive grazing can be used to manage invasive species. In some instances, carefully targeted grazing (sometimes in combination with other treatments) can reduce or maintain the species composition of invasive species.
Submodel
Mechanism
The Reference State (1) transitions to the Rhizomatous Grass State (2) if bluebunch wheatgrass, by dry weight, decreases to below 15 percent or if bare ground cover is increased beyond 35 percent. The driver for this transition is loss of taller bunchgrasses, which creates open areas in the plant canopy with bare soil. Soil erosion results in decreased soil fertility, driving transitions to the Rhizomatous Grass State. There are several other 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 trigger for this transition is improper grazing management and/or long-term drought leading to a decrease in bluebunch wheatgrass composition to less than 15 percent and reduction in total plant canopy cover.
Mechanism
The Reference State (1) transitions to the Shortgrass-Shrub State (3) when Bluebunch wheatgrass is removed from the plant community and needle and thread is subdominant to short statured bunchgrasses such as Sandberg bluegrass. The trigger for this transition is loss of taller bunchgrasses, which creates open spaces with bare soil. Soil erosion results in decreased soil fertility, driving transitions to the Shortgrass-Shrub State. There are several other key factors signaling the approach of transition T1B: 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, intense or repeated fires, and/or heavy human disturbance. Rapid transition is generally realized where livestock are confined to small pastures for long periods of time.
Mechanism
Healthy plant communities are most resistant to invasion however, regardless of grazing management, without some form of active weed management (chemical, mechanical, or biological control) and without prevention the Reference State (1) can transition to the Invaded State (4) in the presence of aggressive invasive species such as spotted knapweed, leafy spurge, and cheatgrass. The Central Rocky Mountain Valleys tend to resists invasion of cheatgrass however repeated heavy grazing or intense human activities can open the interspaces of the bunchgrass community and allow for encroachment. Long-term stress conditions for native species (e.g., overgrazing, drought, and fire) accelerate this transition. If populations of invasive species reach critical levels, the site transitions to the Invaded State. The trigger for this transition is the presence of aggressive invasive species. Species composition by dry weight of invasive species approaches 10 percent.
Mechanism
The Rhizomatous Grass State (2) has lost soil or vegetation attributes to the point that recovery to the Reference State (1) may require reclamation efforts such as soil rebuilding, intensive mechanical and cultural treatments, and/or revegetation. Examples of mechanical treatment may be brush control while cultural treatments may include prescribed grazing, targeted brush browsing, or prescribed burning. Prescribed grazing tactics may include a rest or deferred season rotation with light or moderate grazing intensity. Low intensity prescribed fires to reduce competitive increaser plants such as needle-and-thread and Sandberg bluegrass. A low intensity fire will also reduce Wyoming big sagebrush densities. In areas with potential of annual grass infestation, fire should be carefully planned or avoided. The drivers for this restoration pathway are reclamation efforts along with proper grazing management.
Mechanism
As improper grazing management continues vigor of bunch grasses will decrease, and the shorter grasses and shrubs will increase towards the Shortgrass-Shrub State (3). Prolonged drought will provide a competitive advantage to shrubs allowing them to become codominant with grasses. Shrub canopy will increase. Key transition factors: increase of native shrub canopy cover; reduction in bunchgrass production; decrease in total plant canopy cover and production; increases in mean bare patch size; increases in soil crusting; decreases in cover of cryptobiotic crusts; decreases in soil aggregate stability; and/or evidence of erosion including water flow patterns and litter movement.
Mechanism
Invasive species can occupy the Rhizomatous Grass State (2) and drive it to the Invaded State (4). The Rhizomatous Grass State is at risk if invasive seeds and/or other viable material are present. The driver for this transition is more than 10 percent dry weight of invasive species. The trigger is the presence of seeds and/or other viable material of invasive species.
Mechanism
Invasive species can occupy the Shortgrass-Shrub State (3) and drive it to the Invaded State (4). The Shortgrass-Shrub State is at risk of this transition occurring if invasive seeds or viable material are present. The driver for this transition is presence of critical population levels of invasive species. The trigger is the presence of seeds or viable material of invasive species. This state has sufficient bare ground that the transition could occur simply due to presence or introduction of invasive seeds or viable material. This is particularly true of aggressive invasive species such as spotted knapweed and cheatgrass. This transition could be assisted by overgrazing (failure to adjust stocking rate to declining forage production), long-term lack of fire, or extensive drought.
Mechanism
Restoration of the Invaded State (4) to the Reference State (1) requires substantial energy input. The drivers for the restoration pathway are 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 the site has transitioned from the Reference State to the Invaded State, the amount of time and resources necessary to transition back to the Reference may will be less than a site that transitioned from the Rhizomatous Grass State. Sites that transitioned from the Rhizomatous Grass State (2) will require more inputs to reestablish native bunchgrasses before it will resemble the Reference State (1). Sites that have transitioned from the Degraded State (3) to the Invaded State (4) may be severely lacking 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 bunchgrasses have been drastically reduced the Invaded State (4) can return to the Rhizomatous Grass 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.
Mechanism
If invasive species are removed the site could return to the Degraded State (3). Without sufficient remnant populations of preferred plants the Invaded State (4) is not likely to return to any of the other states. The driver for the reclamation pathway is weed management without reseeding. The trigger is invasive species control. The invading species cause a significant increased soil loss due to lack of ground cover (Lacey et al. 1989).
Model keys
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