Foothill Swale
Scenario model
Current ecosystem state
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Management practices/drivers
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- Transition T1A More details
- Restoration pathway R2A More details
- Transition T2A More details
- Transition T2B More details
- Transition T2C More details
- Transition T3A More details
- Restoration pathway R4B More details
- Restoration pathway R4A More details
- Restoration pathway R5A More details
- Restoration pathway R5B More details
- Transition T5A More details
- Restoration pathway R6A 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
This state consists of two major plant communities, 1) Basin Wildrye with low Basin big sagebrush shrub cover and 2) Wheatgrasses/Basin Wildrye with basin big sagebrush. In community 1.1, the grasses are the dominant component. In community 1.2, grasses may be dominant or co-dominant with basin big sagebrush.
Submodel
Description
This state occurs when there are low frequencies of fire coupled with heavy grazing, and/or drought. The rabbit brush increases due to the disturbance and decrease of competition from the grasses and then is phased out by basin big sagebrush. The basin big sagebrush continues to increase as perennial grasses are weakened by drought or improper grazing. The grasses remain dominant, however their composition does change. Streambank wheatgrass increases to become dominant or co-dominant with basin wildrye. Streambank wheatgrass is more tolerant to grazing than basin wildrye which has elevated growing points. If grazed consistently heavy in the spring and early summer when basin wildrye is palatable, it will decline. Streambank wheatgrass can handle periodic flooding as well as drought conditions fairly well. This state is moderately stable, although susceptible to erosion due to the increase of bare ground under and around sagebrush canopy.
The plant composition of this state is 50-65% perennial grasses, 5-10% forbs and 20-35% shrubs. The annual production drops to around 1500 pounds an acre in an average year. If fire is not introduced to this system it may begin to cross a threshold to a sagebrush dominated state. During this phase Kentucky bluegrass and small amounts of cheatgrass and lambsquarters may begin to invade the site.
This state arises when there has been prolonged fire suppression along with heavy grazing and/or drought. Basin big sagebrush is now the dominant species contributing over 35% of the production of the site. Streambank wheatgrass and western wheatgrass are the major grasses in this scenario, along with sandberg bluegrass, bottlebrush squirreltail, and Indian ricegrass. These are all grasses that are favored as soils are drying. There is little to no basin wildrye left in this community. Kentucky bluegrass and cheatgrass may invade as native grasses are weakened due to heavy grazing and increased competition by basin big sagebrush.
The hydrology of the site is beginning to be altered as the water table lowers due to the lack of grasses. This state’s annual production may be around 800-1200 pounds an acre in an average year. If heavy grazing continues to occur shrubs will continue to increase and perennial grasses will begin to be replaced by annuals such as cheatgrass.
This state may return to the reference state through Prescribed fire or brush management by chemical or mechanical means followed by reseeding. A prescribed grazing plan should be applied which should include a deferment period of 2 to 3 years or more depending on the site to allow.
Rush, big sagebrush, fleabane, herbaceous cinquefoil, bottlebrush squirreltail, foxtail barley, equisetum - horsetail, and rabbitbrush have increase and become dominant plants in this state. The hydrologic function of this community is still intact throughout the entirety of the swale. Meaning, there is no bench or entrenched channel. The water has access to the entirety of the swale for flooding and energy dissipation purposes. This state is a very unstable state at the edge of a very major threshold and this would be the latest time to treat the site, with the least amount of energy, and expect to restore it to the reference plant community. Without treatment there is high probability of a transition to a greatly degraded state with a high flow event that could permanently alter the hydrologic function of the site.
Upland site degradation is a huge influence in allowing the progression of the transition from a site with functioning hydrology and preferred plant communities to this highly unstable community. Uplands that develop dense, aged sagebrush stands with little understory dewater a swale by increasing overland flow and evaporative loss and decreasing a site’s ability to capture and store water. The removal of grasses and herbaceous litter from the soil surface decreases the site’s ability to slow water and allow for infiltration. Thus, water that once could have been safely transported, infiltrated, stored and moved to the swale at a later period is now added to the already erosive overland flow at the same time. Meaning, larger amounts of water and sediment are running onto the swale more rapidly in a shorter period of time. These minor changes in the microclimate, especially on the periphery of the swale, are enough to allow for the sagebrush to continue advancing into the swale along with other obligate upland species and further perpetuating the drying.
Submodel
Description
This is a degraded state and the hydrology of this site has been altered. The plant community and surface debris are no longer capable of slowing runoff and dissipating the water’s erosive energy. In flow events, fine organic materials are not present to stabilize soil, slow water and allow infiltration. Instead, water from the uplands builds energy as it collects in the swale and begins to form a channel. As the water becomes more channelized, the swale becomes even less capable of dissipating the energy and channelization increases moving down the system and a head-cut start moving up the system. The channel also begins to drain subterranean water, further dewatering the system in a self-perpetuating feedback loop. Soils in these areas may see drastically reduced A horizons (7” or less).
Due to the dewatering trend that has occurred in the sagebrush dominated swale State 2, production of this altered community is drastically reduced to 500-700 pounds per acre. Diversity is severely restricted to three or four different species with rush being one of the major components. The bare ground is also increased to 10-15%, or higher. With the lower water availability this allows greasewood to possible invaded in this state. More research is needed into the greasewood plant community in this area.
This state has two fluctuating phases. Both phases have an entrenched channel where water has no access to the swale floodplain and although vegetation in the channel may return to a community similar to the original reference state (if not a little wetter), the majority of the swale remains in the degraded sagebrush dominated state producing only a fraction of its original potential. The first community is the least stable with high levels of erosion occurring with any flow event. There is no vegetation on the sidewalls or the bottom of the channel. It has a distinctly V shaped channel profile that widens and deepens with every flow event. The second community is where healing is occurring and he bottom of the channel has become re-vegetated. The vegetation is similar to that of the reference community with some exception. Since there is the same amount of water consolidated to a smaller are, the soils have a greater potential to show gleying and redoximorphic features that indicate low oxygen environments that are associated with the presence of a water table. Thus, plants that often inhabit the channel are those that have a greater tolerance for flooding. This means that often the amount of obligate and facultative wetland species are increased beyond that of the reference plant community. The channel vegetation helps to hold the channel in minor to moderate flooding events and prevent further degradation. Often sites in this phase develop U shaped profiles.
Submodel
Description
A system dominated by rabbitbrush is a system in which the vegetation has been removed by chemical treatment, physical means (mowing) or fire often in attempted to remove invading sagebrush. Rabbitbrush is a re-sprouter and will increase after disturbance.
Submodel
Description
This community is a man-made community. To get to this state requires a lot of inputs and hard work, but it can be done. Time, energy and resources are needed to restore the water table to the floor of the swale and not the bottom of the channel.
Submodel
Description
With Basin big sagebrush increasing and sagebrush decadence increasing, cover changes in this communities can brought on by prolonged drought, lack of fire, surface disturbances, (i.e. road and pipeline development and off road vehicle (OHV) use), and improper grazing use can create alterations in the plant community that can leave the soils at risk for erosion and alter the hydrological function. Improper grazing of perennial grasses during growth has favored non-native invasive species, primarily cheatgrass and/or Russian thistle, to co-dominate the understory. Few remnant plants may still persist under shrubs, but re-establishment and dominance by perennial grasses will not occur following a fire, or with the removal of grazing animals in the natural time frame.
Submodel
Mechanism
Sagebrush encroachment with increasing sagebrush decadence and cover in adjacent upland communities brought on by prolonged drought, lack of fire, and improper grazing use can create alterations in the plant community that can leave the soils at risk for erosion and alter the hydrological function. The mean fire return interval (FRI) is 12 -25 years for mesic habitats (Boyd et. al., 2014) Also, lack of wet periods to drown out Big sagebrush can cause this shift from State 1 - Reference State to State 2 - Basin Big Sagebrush Dominated Swale.
Mechanism
State 1 can be restored from the sagebrush dominated swale through fire or some kind of sagebrush removal and proper grazing use by both domestic animal and wildlife use. Management practices that restore upland community health and functioning are critical to restoring a sagebrush dominated swale to the reference state as well as those done in the swale itself. Such practices can include prescribed fire and/or shrub management. This needs to be used in conjunction with proper grazing management. Several wet years in a row can also decrease big sagebrush, as big sagebrush does not like to have it roots in water for extended periods of time.
Mechanism
This is a very quick transition. Due to the lack of soil protection large flow events quickly destabilize the site and it transitions to the state with altered hydrological function (3). Anything that further reduces ground cover, like improper grazing use and continued drought, has potential to quicken this transition. Fire suppression and lack of shrub management in decadent sagebrush uplands continue to promote altered hydrologic function and also aid in destabilizing the swale.
This community becomes unstable, affects soil health and the hydrologic function as it is invaded by big sagebrush. The lack of adequate herbaceous cover to dissipate water velocity and encourage infiltration result in the formation of gullies and head-cuts.
Mechanism
Repetitive burning of big sagebrush favors rabbitbrush and perennial grasses, especially Basin wildrye. Mechanical and chemical removal of sagebrush can often release rabbitbrush on this site. This may be a timing of treatment issue or one related to the weather patterns in years surrounding the treatment.
Mechanism
The introduction of annual grasses (cheatgrass) and forbs to the site.
Mechanism
Returning to the reference state from either of the two communities phase in State 3 would be time, resource, and energy intensive. The water table needs to be restored to the floor of the swale and not the bottom of the channel. Often a large amount of dirt work, brush removal and the installation of check dams are required to reclaim the swale community. Check dam structures are used in an attempt to stop head-cuts, slow water, and catch sediments all in hopes of raising both the channel and the water table to allow for flooding access to the entire swale and returning the hydrologic function. Reclaiming these swale sites, also, include fixing all the problems that initially contribute to the degradation, including management practices that improve the contributing upland communities. A swale cannot be restored by only changing problems within the site itself. The swale’s health and success in restoring the functioning is directly tied the health and function of the surrounding uplands.
Mechanism
Often the only way to transition from this state to a preferred functioning community (reference community) that is not dominated by sagebrush is by means of chemical treatment of the rabbitbrush. Repetitive treatment is often needed.
Mechanism
Continued sagebrush encroachment from untreated uplands and improper grazing use can contribute to the transitioning of this rabbitbrush state to that of one dominated by sagebrush.
Mechanism
This restorative pathway from the State 5 to the State 1 is very intensive. Often successful on small scales over very long periods of time, large scale restoration projects are not often able to be fully restored. This pathway would require continued sedimentation, proper grazing use, and proper hydrologic contributions. This community may reestablish the same hydrological function as in the reference state if the contributing upland sites provide the hydrologic contributions.
Mechanism
This community becomes unstable, affects soil health and the hydrologic function as it is invaded by big sagebrush. The lack of adequate herbaceous cover to dissipate water velocity and encourage infiltration result in the formation of gullies and head-cuts. This is a very quick transition. Due to the lack of soil protection large flow events quickly destabilize the site and it transitions to the state with altered hydrological function (3). Anything that further reduces ground cover, like improper grazing use and continued drought, has potential to quicken this transition. Fire suppression and lack of shrub management in decadent sagebrush uplands continue to promote altered hydrologic function and also aid in destabilizing the bottom.
Mechanism
Sagebrush encroachment with increasing sagebrush decadence and cover in adjacent upland communities brought on by prolonged drought, lack of fire, and improper grazing use can create alterations in the plant community that can leave the soils at risk for erosion and alter the hydrological function.
Mechanism
To restore the site to the current potential state extreme inputs are necessary. This transition is from a big sagebrush dominated state, to a state that has been seeded with introduced or native perennial grasses. High energy inputs are needed for this transition. Sagebrush will need to be removed with vegetation treatment techniques (I.e. chemical, mechanical, or fire) and introduced or native species that are adapted to the area and adapted to management needs have been seeded and become established. Proper grazing use by both domestic animal and wildlife needs to occur. Often successful on small scales over very long periods of time, large scale restoration projects are not often able to be fully restored. This pathway would require continued sedimentation, proper grazing use, and proper hydrologic contributions.
Management practices that restore upland community health and functioning are critical to restoring a sagebrush dominated bottom to the current potential state. Such practices can include shrub management, and reseeding. Erosion control structures may be necessary. This needs to be used in conjunction with proper grazing management. Several wet years in a row can also decrease big sagebrush, as big sagebrush does not like to have it roots in water for extended periods of time.
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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.