Natural Resources
Conservation Service
Sandy Green River Basin (Sy GRB)
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
- Restoration pathway R3A More details
- Restoration pathway R3B More details
- Transition T3A More details
- Restoration pathway R5A More details
- Restoration pathway R5B More details
- Restoration pathway R5C More details
- Restoration pathway R5D 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 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 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, 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. 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 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 as Sandberg bluegrass and, rhizomatous grasses and grass-likes, such as thickspike wheatgrass and needleaf sedge. Mid-stature bunchgrasses such as Indian ricegrass and needleandthread are scarce or absent. There are two community phases in the Grazing Resistant State: the Big Sagebrush/ Thickspike Wheatgrass Plant Community and the Thickspike Wheatgrass/Big Sagebrush 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 Big Sagebrush/Thickpsike Wheatgrass Plant Community is very resistant to change and therefore is common on this site. 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 this 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 resiliency of the Big Sagebrush/Thickspike Wheatgrass Plant Community is that 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 grazing, especially in early season pastures and in small acreage pastures, ground cover can decrease to a point that the site will transition to the Bare Ground State (3), particularly during drought conditions if stocking is not reduced.
Submodel
Description
This state contains one community, the Big Sagebrush/Bare Ground Community (3.1). It is characterized by sparse herbaceous plant cover dominated by big sagebrush and bare ground.
Communities in the Bare Ground State (3) have crossed a threshold (T1-3 or T2-3) because of soil erosion, loss of soil fertility, and/or degradation of soil properties. Soil erosion affects the hydrology, soil chemistry, soil microorganisms, and soil physics to the point where intensive restoration is required to restore the site to another state or community. Simply changing grazing management may not create sufficient change to restore the site within a reasonable period. It will require a considerable input of energy to move the site back to the Reference State (1).
The Bare Ground State (3.0) is at high 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. This puts the community at risk of transitioning to the Disturbed State (4).
Submodel
Description
This state is characterized by the amount of rabbitbrush on the site. It also has a component of annual forbs and substantial bare ground. It 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 tebuthiuron), 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 when 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
Mechanism
The driver for Transition T1-2 is continuous spring grazing and/or long-term drought. Continuous spring grazing and/or 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, is typically the first species to decline (Natural Resources Conservation Service, 2007). 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 toward less productive species. While bare ground may not change, 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 bunchgrasses 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. 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.
Mechanism
The driver for Transition T1-3 is continuous high intensity grazing and/or long-term drought. The Reference State (1) transitions to the Eroded State (3) if plant canopy cover declines significantly or total annual aboveground biomass production falls below 300 pounds per acre. The trigger for this transition is the loss of understory, which creates open spots with bare soil. Soil erosion is accompanied by decreased soil fertility driving the transitions to the Bare Ground State. Several other key factors signal the approach of transition T1B: an increase in soil physical crusting, a decrease in soil surface aggregate stability, and/or evidence of erosion, including water flow patterns, development of plant pedestals, and litter movement.
Mechanism
The driver for this transition 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 Reference State (1) may transition to the Disturbed State (4) if a soil disturbing activity has occurred. Sprouting shrubs such as rabbitbrush increase from ground disturbances 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 a seed source exists, aggressive invasive species, such as cheatgrass, may be present, but are not expected to dominate the site. However, it is projected that annual invasives may effect site dynamics under future climate change scenarios. To prevent this transition, the site will require proper reclamation using the most current science and technology available to restore native vegetation and prevent invasive dominance. In some instances, it may not be possible to prevent this transition. In cases where total 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 a transition to the Disturbed State (4). The resulting lower biomass production, reduced litter, and increased bare ground in this community can promote invasion of undesirable species. The site transitions to the Disturbed State when populations of invasive species reach critical levels.
Mechanism
The drivers for this restoration pathway are removal 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. 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 to the Bare Ground State is continuous high intensity grazing. Examples include calving pastures and small acreage horse pastures where rotational grazing is not employed. Extended drought period may provide a trigger to accelerate this process. The Bare Ground State is typified by old age sagebrush stands with very little herbaceous understory. Bare ground patch size has increased to the majority of the interspaces between sagebrush plants.
Mechanism
The driver for transition to the Disturbed State is an increase in the disturbance cycle (i.e. grazing, drought, fire, mechanical, chemical, biological treatments). 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.
Mechanism
This state has lost soil or vegetation attributes to the point that recovery to the Reference State will require a combination of long-term grazing management (changing season of use to allow frequent rest or deferment during the critical growth period) and chemical, biological or mechanical treatments, and often re-seeding. Seeding may become cost prohibiting as a restoration practice used alone. With reduced organic matter and loss of soil, soil amendments may be needed to have a successful seeding. Care must be taken with any re-seeding operation to prevent the introduction of invasive species, such as cheatgrass, to areas where these species are not currently present.
Mechanism
The drivers for this restoration pathway are mechanical, biological and chemical treatments with only 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.
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 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). Fire is not usually possible due to lack of understory fuels to carry the fire. In fact, the Eroded State is characterized by monotypic decadent sagebrush stands because they are fireproof.
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. This most often occurs through achieving the Bunchgrass Plant Community first. 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. 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 Eroded State (3) if disturbed areas result in total topsoil removal, are abandoned (no re-seeding) 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. 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 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.
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