Loamy Platte Valley (Ly PV)
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
- Transition T1-2 More details
- Transition T1-3 More details
- Transition T1-4 More details
- Transition T1-5 More details
- Restoration pathway R2-1 More details
- Transition T2-3 More details
- Transition T2-4 More details
- Transition T2-5 More details
- Restoration pathway R3-1 More details
- Restoration pathway R3-2 More details
- Transition T3-4 More details
- Transition T3-5 More details
- Transition T4-5 More details
- Restoration pathway R5-1 More details
- Restoration pathway R5-2 More details
- Restoration pathway R5-3 More details
- Restoration pathway R5-4 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 30 percent.
Dominant shrub species is Wyoming Big Sagebrush in the Reference State (1), with some instances of, mountain big sagebrush at the upper end of the precipitation range.
Two important processes occurring in this state result in plant community changes within Reference State: sagebrush killing disturbances (browse, insects, drought, fire) and time without those disturbances. These processes are 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. This is generally a long-term process, although, improper grazing management may accelerate the rate of increase for woody species.
The shift from the Big Sagebrush/Bunchgrass or Bunchgrass/Big Sagebrush Plant Communities is dependent on sagebrush killing disturbances such as fire, drought, browse, and insects. Management actions can and are often used to mimic these processes through mechanical and chemical treatments. Prescribed fire is not often used on this site due to current land uses and lack of fuels and adequate burn windows.
Submodel
Description
The Grazing Resistant State (2) is characterized by an herbaceous layer dominated by short-statured bunchgrasses such such as Sandberg bluegrass and, rhizomatous grasses and grass-likes, and/or mat forbs such as Hood’s phlox, pussytoes, and sulfur flowered buckwheat. Mid-stature bunchgrasses such as Indian ricegrass, needleandthread, muttongrass, and bottlebrush squirreltail have become scarce or absent and are commonly found under sagebrush plants. There is an increase in green rabbitbrush along with annual forbs and cheatgrass. There is one community in the Grazing Resistant State: the Big Sagebrush/Rhizomatous Wheatgrass-Sandberg Bluegrass -Mat Forb Plant Community (2.1).
The site crosses the threshold to the Grazing Resistant State (2) from the Reference State (1) when desirable mid-stature bunchgrasses lose dominance. Once the key species become scarce, it is unlikely that they have sufficient reproductive capability (seed source, tillering, or resprouting) to recover dominance in a reasonable time frame without extra energy being added to the system.
The Plant Community in the Grazing Resistant State (2) is very resilient and therefore common on Loamy sites in this MLRA. In many cases, the transition to the Grazing Resistant State (2) may have occurred many decades ago during an era of higher stocking rates and continuous grazing during the growing season. However, continual grazing during the critical growth period (roughly May-June) at proper stocking rates will facilitate the transition to this state and maintain it in a stable state. While dominance by rhizomatous grasses makes the return to the Reference State (1) plant community difficult, it also makes the site resistant to further degradation except in cases where overstocked or in the case of prolonged drought with full stocking. The main factor creating high resiliency of the Big Sagebrush/Rhizomatous Wheatgrass-Sandberg Bluegrass-Mat Forb Plant Community is that the bluegrass and rhizomatous grasses are highly grazing tolerant. Sandberg bluegrass and rhizomatous grasses are low to the ground, so, even under heavy grazing, enough biomass remains for the grasses to maintain plant vigor. Rhizomatous grasses successfully reproduce through underground rhizomes. The rhizomatous grasses can form mats that provide soil protection by protecting the soil from raindrop impact, decreasing the risk of soil erosion. However, overall soil health is lower than the reference state, primarily due to a reduction in soil organic matter due to a reduction in litter. The decreased infiltration is due increased bare ground patch size and lack of litter that acts as mulch in retaining soil moisture and retarding runoff. Under high intensity early season grazing, especially by in calving pastures and in small acreage horse pastures, ground cover decreases to a point that the site will transition to the Bare Ground State (3).
Submodel
Description
Herbaceous canopy cover in the Big Sagebrush/Bare Ground Community (3.1) is significantly reduced. Annual production is approximately half of the Bunchgrass Plant Community (1.1). Perennial bunchgrasses (e.g., Indian ricegrass, bottlebrush squirreltail, and needleandthread) exist only in low densities and protected under the sagebrush canopy. This community tends to be dominated by Wyoming big sagebrush (>25% cover) and bare ground in large connected patches in the interspaces of the shrub canopy. The majority of annual production is from big sagebrush so this site provides very little value for grazing. Sufficient quantity of fine fuels necessary to carry a fire. Therefore, fire is no longer a driver of ecological dynamics.
Sparse vegetation creates low levels of foliar and basal cover. This, in turn, leads to low litter production, which is combined with reduced ability to retain litter on site. Soil is exposed to wind and water erosion in the plant interspaces. These factors combine to create a decrease in soil organic matter. Reduced litter cover, combined with reduced herbaceous cover, results in higher soil temperature, poor water infiltration rates, and high evaporation, thus favoring species which are more adapted to drier conditions. Soil fertility is reduced, soil compaction is increased, and resistance to soil surface erosion has declined compared to the other states. This community has lost most, if not all, of the attributes of a functioning, healthy rangeland, including good infiltration, minimal erosion and runoff, nutrient cycling, and energy flow. This state commonly occurs in feeding areas, salting locations and confined horse pastures.
Submodel
Description
This state is characterized by the amount of rabbitbrush invasion on the site. It also has a component of annual forbs and substantial bare ground.
Is occurs with 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 heavy equipment/construction or a mowing/chaining/harrow type sage treatment), chemical (including 2,4-D or tebuthiron), or biological (including browse and/or insects). Fire could be a factor in maintaining this plant community perpetually by stimulating sprouting shrubs (rabbitbrush) and killing sagebrush. This is usually only a concern annual weeds are prolific on the site during wet cycles that boost their production.
Removal of shrubs without proper grazing management can lead to an increase in bare ground and erosion of the upper soil horizon. Consequences of this are decreased soil fertility or even soil erosion, soil crusting, and decrease of soil surface aggregate stability.
Submodel
Description
As part of succession, all sites that are severely disturbed will go through this plant community as part of their restoration. Weather is the largest determining factor in how long a site will be in this plant community phase, but is approximately 2-5 years on sites that use Best Management Practices for site restoration (http://www.uwyo.edu/wrrc/). Site has low potential for recovery. Seeding is needed to restore functional structural groups.
Submodel
Mechanism
The driver for transition from the Reference State to the Grazing Resistant State (T1-2) is continuous spring grazing and/or long-term 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, and bluebunch wheatgrass, a long-lived perennial that has elevated growth points, are typically the first species to decline (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 shrub canopy.
Once mid-stature bunchgrasses 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 extra energy being added to the system. 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 woody canopy cover, but rather on 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 driver for transition from the Reference State to the Eroded State (T1-3) is continuous high intensity early season grazing. Drought can accelerate this transition.
Indicators of this transition include significant decline in plant canopy cover or total annual aboveground biomass production below 200 pounds per acre. The primary indicator of this transition is the loss of understory, which creates open spots with bare soil between the sagebrush canopy. Soil erosion causes decreased soil fertility and infiltration, triggering the transition to the Eroded State. Several other key factors signal the approach of a threshhold: 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 driver for transition from the Reference State to the Disturbed State (T1-4) 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. 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. 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 unavoidable to prevent this transition.
Long-term stress conditions for native species (e.g., improper grazing management, drought, and fire) will alter plant community composition and production over time and may hasten the transition. The resulting lower biomass production, reduced litter, and increased bare ground in this community can promote invasion of undesirable species.
Mechanism
The driver for transition from the Reference State to the Highly Disturbed State (T1-5) is a topsoil removing event with mechanical equipment. Examples include construction sites, oil and gas activity, and borrow areas.
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, proper grazing management 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).
Mechanism
The driver for transition from the Grazing Resistant State to the Eroded State (T2-3) is continuous high intensity early season grazing from the Big Sagebrush/Rhizomatous Wheatgrass Community (2-1). Examples include calving pastures and small acreage horse pastures where rotational grazing is not employed, but 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 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. grazing, drought, fire, mechanical, chemical, biological treatments) combined with continuous high intensity grazing. Examples include 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.
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 or even 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).
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
The Eroded State (3) has lost soil or vegetation attributes to the point that recovery to the Reference State (1) will require a combination of grazing management (changing season of use to allow frequent rest or deferment during the critical growth period) and chemical, biological or mechanical treatments, and reseeding. Seeding may be cost prohibitive as a restoration practice used alone. With reduced organic matter and loss of soil, soil amendments and/or mulch may be needed for restoration success. Restoration has occurred by mowing without re-seeding, but the grazing regime in this instance is low stocking density and winter only use.
Mechanism
Restoration from the Eroded 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 a sagebrush killing event with continuous high intensity early season grazing. The event could be severe drought, flooding, insects, disease, or a sagebrush treatment such as mechanical (including heavy equipment/construction or a mowing/chaining/harrow type sage treatment), chemical (including 2,4-D or tebuthiron), or biological (including browse and/or insects). Fire is not usually possible due to lack of understory fuels to carry the fire. In fact, the Eroded State (3) is characterized by monotypic decadent sagebrush stands because they are fireproof.
Mechanism
The driver for transition from the Reference State to the Highly Disturbed State (T1-5) 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, 2015).
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) can be restored to the Reference State (1) if appropriate seedbed preparation and seed mixes are used, and weather conditions are conducive to seedling establishment. Weather is the largest determining factor in determining time and success, but the process can be accelerated with Best Management Practices for site restoration (http://www.uwyo.edu/wrrc/ ). There is low potential for recovery without significant inputs of energy and resources if topsoil has been removed. Seeding is needed to restore functional structural groups, and proper seedbed preparation is key to restoring ecological processes on the site.
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. Weather is the largest determining factor in determining time and success, but the process can be accelerated with Best Management Practices for site restoration (http://www.uwyo.edu/wrrc/ ). 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 past and post-seeding grazing management of the area.
Mechanism
The Highly Disturbed State (5) can transition the Eroded State (3) if disturbed areas result in total topsoil removal and are abandoned and climate is favorable for 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.
If topsoil was not physically removed, and there is a viable seedbank in the soil, recovery is possible without re-seeding as long as adequate rest from herbivory is provided to allow seedling establishment. Rest from herbivory is recommended during dry years to prevent further soil loss as well as in wet years to allow seedling establishment.
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 species such as rabbitbrush. 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 scraps some of the soil surface during the removal process.
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.