Loamy Calcareous Green River Basin (LyCa GRB)
Scenario model
Current ecosystem state
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Management practices/drivers
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- 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 T2C More details
- Restoration pathway R3A More details
- Transition T3A More details
- Transition T3B More details
- Transition T4A More details
- Restoration pathway R5A More details
- Restoration pathway R5B More details
- Restoration pathway R5C 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
The Reference State consists of three Plant Communities: the Big Sagebrush/Bunchgrass Community (1.1) the Bunchgrass/Big sagebrush Plant Community (1.2) and the Bunchgrass Community (1.3). Each community differs in percent composition of bunchgrasses and percent woody canopy cover. Forbs are a minor component on this site. Woody canopy cover is less than 25 percent.
The Loamy Calcareous site potential is slightly less than the Loamy site in this LRU, due to the restrictive nature of the shallow calcic horizon that occurs in it. The diversity in plant species allows for drought tolerance, and natural plant mortality is very low. These plants have strong, healthy root systems that allow production to increase significantly with favorable moisture conditions.
The dominant shrub species is Wyoming Big Sagebrush in the Reference State (1).
Two important processes occurring in this state result in plant community changes within Reference State: sagebrush killing disturbances (browse, insects, and drought) and long periods of time without those disturbances. This process of plant community change over time is generally referred to as “natural succession.”
The shift from the Bunchgrass Plant Community (1.3) to the Bunchgrass/Big Sagebrush Plant Community (1.2) and subsequently to the Big Sagebrush/Bunchgrass Plant Community is dependent on an increase of woody cover. Without sagebrush killing disturbance, shrubs will increase on this ecological site even with proper grazing management. Improper grazing management may accelerate the rate of increase for woody species and/or result in higher shrub canopy cover than in the Reference State.
The shift from the Big Sagebrush/Bunchgrass or Bunchgrass/Big Sagebrush Plant Communities is dependent on sagebrush killing disturbances such as drought, herbivory, disease and insect outbreaks. Management actions can and are often used to mimic these processes through mechanical and chemical treatments.
The Reference State is well adapted to Cool Central Desertic Basins and Plateaus climatic conditions. The diversity in plant species allows for drought tolerance, and plant mortality is low. These plants have strong, healthy root systems that allow production to increase significantly with favorable moisture conditions. Abundant plant litter is available for soil building and moisture retention and is properly distributed with very little movement off-site. Biological soil crusts play an important role in protecting the soil surface as well as carbon, nutrient, and water cycles, particularly moss and lichen under the sagebrush canopy and cyanobacteria in the interspaces (Natural Resources Conservation Service, 1997) (Rosentrater & M. Bowker, 2007). They are a source of carbon to soils, and not only do they convert atmospheric nitrogen into bio-available nitrogen, but they also secrete compounds that increase the bio-availability of phosphorus (Rosentrater & M. Bowker, 2007). This State provides for soil stability and a properly functioning hydrologic cycle. The soils associated with this site hold moderately large amounts of soil moisture, providing a very favorable soil-water-plant relationship. Plant community phases can occur in large contiguous blocks or in a small to large mosaic pattern, but typically this plant community is maintained within a larger mosaic at the landscape level with the other plant communities phases identified in the Reference State (Bukowski & Baker, 2013).
Mechanical and chemical treatment of shrubs have replaced natural sagebrush killing events in many cases. However, chemical treatments impact nontarget species, particularly broad-leafed species (forbs and shrubs) differently than natural. Chemical treatment of sagebrush with tebuthiuron can have impacts the understory, depending on application rate (Wyoming Wildlife Consultants, LLC, 2009). Many historical treatments with continuous grazing both pre- and post-treatment have resulted in a transition to the Disturbed State. Good historical records of the pre-treatment State are not available, but it is presumed that they were already in the Grazing Resistance State, and thus this result may not apply to treatments planned on communities in the Reference State.
Submodel
Description
The Grazing Resistant State is characterized an herbaceous component dominated by thickspike wheatgrasses Sandberg bluegrass and/or mat-forming forbs, with limited mid-stature bunchgrasses. Once mid-stature bunchgrasses become scarce, it is unlikely there will be sufficient reproductive capability (seed source, tillering, or re-sprouting) to recover dominance in a reasonable time frame without extra energy being added to the system (Cagney, et al., 2010). The plant community is highly resistant to changes in composition, due to the dominance and competition of grazing tolerant species. However, the community can be restored back to the Reference State (1) with sagebrush treatment (chemical, mechanical, or biological brush management) and grazing deferment followed by a grazing system that allows periodic rest during the critical growth period. Seeding maybe needed in some instances to achieve desired results.
Submodel
Description
This state contains one community, the Big Sagebrush/Bare Ground Community (3.1). It is characterized by very old sagebrush stands with very little understory between the sagebrush canopy. Bare ground patch sizes are very large and comprise the majority of the interspaces between sagebrush plants.
Communities in the Bare Ground State (3) have crossed a threshold (T1-3 or T2-3) due to degradation of dynamic soil properties such as organic matter, fertility, and infiltration caused by soil erosion. Soil erosion affects the hydrology, soil chemistry, soil microorganisms, and soil physics to the point where intensive restoration is required to return the site to another state. Simply changing grazing management will not create sufficient change to restore the site within a reasonable time period. It will require a considerable input of energy to move the site back to the Reference State (1).
The Bare Ground State (3) is at moderate risk of weed invasion due to the high percentage of bare ground. Many invasive species are adapted to low soil fertility, high soil temperatures and low soil moisture content. Furthermore, this state is at risk of transitioning to the Disturbed State (4) if mechanical treatments are applied without consideration for seeding or grazing management.
Submodel
Description
This state contains one plant community, the Rabbitbrush/Rhizomatous wheatgrass plant community. It is characterized by rabbitbrush dominance and a perpetual state of disturbance as evidenced in pasture corners, gravel pits and areas repeatedly treated to kill sagebrush.
Submodel
Mechanism
The drivers for transition from the Reference State to the Grazing Resistant State are continuous low intensity spring grazing and/or severe drought.
Continuous spring grazing and/or extended drought can lead to a decline in palatable mid-stature bunchgrasses. Indian ricegrass, a short-lived perennial that requires more frequent seed production to provide an adequate seedbank (Natural Resources Conservation Service). Bottlebrush squirreltail will also decline with grazing pressure and lack of disturbances that kill sagebrush. Needleandthread is more grazing tolerant, but will eventually decline in plant density and vigor. As bunchgrasses diminish or die during periods of stress, low- stature bunchgrasses and rhizomatous grasses gain a competitive advantage, creating a shift in species composition towards less productive, shorter species. While bare ground may not change significantly, the pattern of bare ground will shift to larger gaps in the canopy and fewer herbaceous plants between shrubs. Many of the remaining desirable bunchgrasses will be only found in the understory of the sagebrush canopy.
Once mid-stature bunchgrass species become scarce, it is unlikely that they have sufficient reproductive capability (seed source, tillering, or re-sprouting) to recover dominance in a reasonable time frame without management changes and extra energy being added to the system (Cagney, et al., 2010). When the understory vegetation has been degraded to this point, the transition to the Grazing Resistant State (2) can occur from either the Bunchgrass/Big Sagebrush Plant Community (1.2) or the Big Sagebrush/Bunchgrass Plant Community (1.1). The transition is not dependent on the increase of shrub cover, but rather the lack of mid-stature bunchgrasses in the canopy interspaces.
Management should focus on grazing management strategies that will prevent further degradation. This can be achieved through a grazing management scheme that varies the season of use to provide periodic deferment during the critical growth period (roughly May-June). Forage quantity and/or quality in the Grazing Resistant State (2) may be substantially reduced compared to the Reference State, and will dramatically fluctuate in dry vs. wet years.
Mechanism
The drivers for transition from the Reference State to the Bare Ground State is continuous high intensity/long duration grazing. Drought can accelerate this transition.
Indicators of this transition include significant decline in herbaceous cover or total annual aboveground biomass production falls below 200 pounds per acre. The trigger of this transition is the loss of understory, which creates open spots of with bare soil between the sagebrush canopy (>6 foot gap size). Soil erosion is accompanied by decreased soil fertility and infiltration, triggering the transition to the Eroded State. Several other key factors signal the approach of a threshold: an increase in soil physical crusting, a decrease in soil surface aggregate stability, and/or evidence of erosion, including water flow patterns, development of pedestals, and litter movement.
Mechanism
The causes for transition from the Reference State to the Disturbed State (T1C) is an increase in the disturbance cycle (i.e. grazing, drought, fire, mechanical, chemical or biological treatments), often in combination with grazing management that does not provide periodic deferment during the critical growth period.
The transition can occur if multiple soil disturbing activities occur over a relatively short time period, effectively decreasing the disturbance return interval. This could be high intensity/high frequency grazing, machinery, and/or multiple sagebrush treatments. Indicators include an increase in rabbitbrush to dominant levels in the plant community due to ground disturbance that could be either natural (i.e. water movement) or manmade (i.e. high density/high frequency stocking, mechanical treatments or heavy equipment operations). If introduced to the site, invasive species, such as cheatgrass, may be present, but do not often dominate the site. To prevent this transition, the site will require proper reclamation after disturbance using the most current science and technology available to restore native vegetation and prevent invasive dominance. In cases where topsoil loss occurs, it may be impossible to prevent this transition.
Long-term stressors on native species (e.g., improper grazing management, and drought) will alter plant community composition and production over time and may hasten the transition to the Disturbed State (4), but the main trigger is ground disturbance. The resulting lower biomass production, reduced litter, and increased bare ground in this community can promote invasion of undesirable species, but soil chemistry results in more resistance to invasives compared to other sites.
Mechanism
The drivers for this restoration pathway are reduction of woody species and restoration of native herbaceous species by mechanical or chemical treatment of sagebrush, and grazing rest or deferment. If some mid- stature bunchgrasses remain under the sage canopy, light to moderate stocking with periodic critical growth period rest every 2 or 3 years can move the site back to the Reference State (1) combined with a mechanical or chemical sagebrush treatment. Most probable restoration pathway is from Big Sagebrush/Rhizomatous Wheatgrass Community (2.1) to the Bunchgrass Community (1.3). This could take multiple generations of management or could be accelerated with rest or deferment combined with successive wet springs conducive to seed germination and seedling establishment. (Derner, Schuman, Follett, & Vance, 2014). Seeding may be needed to achieve desired results, if seedbank has been depleted.
Mechanism
The driver for transition from the Grazing Resistant State to the Bare Ground State (T2-3) is continuous high intensity grazing from the Big Sagebrush/Thickspike Wheatgrass Community (2.1). Examples include calving pastures and small acreage horse pastures where rotational grazing is not employed, and stocking densities are high. Extended drought periods accelerate this transition. Indicators include very old sagebrush stands with very little understory between the sagebrush canopy. Bare ground patch sizes are very large (>6 foot canopy gaps comprising >30% of transect) and comprise the majority of the interspaces between sagebrush plants.
Mechanism
The driver for transition from the Grazing Resistant State to the Disturbed State (T2-4) is an increase in the disturbance cycle (i.e. drought, mechanical, chemical, biological treatments) and/or continuous high intensity grazing. Examples include pasture corner gates, calving pastures and small acreage horse pastures where rotational grazing is not employed combined with sagebrush treatment (mechanical, chemical, or biological). High stocking densities are soil disturbing, and adding sagebrush treatment(s) to this regime result in an increase in the disturbance cycle. A non-grazing influenced example would be an abandoned gravel pit.
Removal of shrubs without proper grazing management can lead to an increase in bare ground and erosion of the upper soil horizon, and the site can degrade to the Disturbed State (4). Consequences of this transition are decreased soil fertility, soil erosion, soil crusting, and decrease of soil surface aggregate stability. Indicators of the Disturbed state are a shift in shrub dominance away from sagebrush and toward sprouting shrubs such as green rabbitbrush (Chrysothamnus viscidiflorus) or shadscale (Atriplex confertifolia).
Mechanism
The driver for transition from the Grazing Resistant to the Highly Disturbed State (T2-5) is a topsoil removing event with mechanical equipment. Examples include construction sites, oil and gas activity, and borrow areas.
Mechanism
Restoration from the Bare Ground State (3) to the Grazing Resistant State (2) is possible with mechanical, biological and chemical treatments and temporary rest or deferment post-treatment. Due to loss of soil fertility, structure, and organic matter, reference community plants are slow to repopulate the site. Success of this restoration is highly dependent upon climatic factors, and may require successive wet years. This restoration pathway is often unintentionally achieved when the goal is the Reference State (1) because post-treatment management is not sustained in a manner that allows frequent critical growth period rest and/or use levels and recovery periods are not adequate to sustain mid-stature bunchgrasses.
Mechanism
The driver for this transition is multiple sagebrush killing events in rapid succession outside the normal disturbance regime for this site (see Reference State for discussion). It could be mechanical (including shallow disturbances with heavy equipment/construction or a mowing/chaining/harrow type sage treatment), chemical (including 2,4-D or tebuthiuron), or biological (including browse and/or insects).
Mechanism
The driver for transition to the Highly Disturbed State (5) is a topsoil removing event with mechanical equipment, but it can also occur after severe drought, flooding, pests, or disease kills sagebrush, leaving the site with no perennial vegetation. Examples include construction sites, oil and gas activity, and borrow areas. Evidence of climate as a cause for this transition has been captured after the 2012 drought (Clause & Randall, 2014).
Mechanism
The driver for transition from the Disturbed State to the Highly Disturbed State (T4-5) is a topsoil removing event with mechanical equipment. Examples include construction sites, oil and gas activity, and borrow areas.
Mechanism
The Highly Disturbed State (5) is often restored to the Grazing Resistant State (2) unintentionally when inappropriate seed mixes are used and post-seeding grazing does not provide adequate and periodic critical growth period rest. There is low potential for recovery without significant inputs of energy and resources if topsoil has been removed. Seed mixes that mimic an adjacent “reference area” rather than the site potential as described in the Reference State (1) will often result in a plant community resembling the Grazing Resistant State (2) due to pre and post-seeding grazing management of the area.
Mechanism
The Highly Disturbed State (5) can transition the Bare Ground State (3) if disturbed areas result in total topsoil removal and are abandoned and climate is favorable for sagebrush seedling establishment. Wyoming big sagebrush will eventually colonize the site, but because soil conditions are severely altered, little to no under-story can be found. An example of this transition can be found on abandoned oil and gas wells that are 30+ years old where topsoil was not stockpiled and re-spread on the site after proper contouring and ripping, and either no seeding was done or the planting was a failure.
Mechanism
The Highly Disturbed State (5) can transition the Disturbed State (4) if disturbed areas result in only partial topsoil removal, leaving rootstock available for sprouting shrubs such as rabbitbrush or shadscale. This is common for gravel pits and areas disturbed as stockpile areas where soil is placed on the area for any amount of time, and then removed with equipment that scrapes some of the soil surface during the removal process.
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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.