Salty Bottomland
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
- Transition T1A More details
- Restoration pathway R2A More details
- Transition T2A More details
- Restoration pathway R3A 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 site occurs on alluvial floodplains and benefits from occasional deep wetting due to additional run-on water received from adjacent uplands. The soils are deep, well drained, and salt affected. This site may intergrade with Salt Meadow sites. The reference plant community of the Salty Bottomland site is a grass-shrub mix characterized by alkali sacaton, western wheatgrass, fourwing saltbush and greasewood. Perennial forbs are typically a minor component of the plant community. In years that receive above-average spring precipitation, annual forbs and grasses may occur in high relative abundance. Soil drying due to blocked or redirected water flow may favor deeper-rooted shrubs and initiate the transition to the Shrub-dominated State. Loss of grass cover, resource competition by shrubs, and soil sealing may also facilitate the transition to the Shrub-Dominated State. The continued loss of grass cover in conjunction with soil sealing, increased overland flow, and resulting erosion may initiate the transition to the Gullied State.
This site is a shrub-grass mixture characterized by mid-grasses, alkali sacaton and western wheatgrass. Inland saltgrass withstands a shallower water table, ponding, and high salt concentration better than alkali sacaton. The characteristic shrubs are black greasewood and fourwing saltbush. Big sagebrush occurs where this site is less salty and is gradually replaced by shadscale as salt increases. Perennial forbs are a minor component of the plant community. Annual forbs and grasses occur in relative abundance during the spring in years which have above average growing conditions. When the potential plant community deteriorates, there is a marked increase in relative abundance of shrubs, cacti, and perennial and annual forbs. With severe vegetative deterioration, the site will consist predominantly of shrubs but can also be dominated by greasewood, sagebrush, annual forbs, and annual grasses, with lesser amounts of perennial grasses and large areas of unprotected soils. The reference state is maintained by recurring fire (fire disclimax).
Submodel
Description
Shrub-Dominated: This state is characterized by the predominance of shrubs, especially greasewood. On areas with higher salt concentrations, greasewood often occurs as the sole dominant. Less commonly, greasewood occurs as a codominant with fourwing saltbush or shadscale saltbush; these areas typically have little herbaceous understory. On areas that are less salt-affected, greasewood may coexist with big sagebrush; these areas will typically have a greater understory of grasses, and alkali sacaton often occurs in widely spaced clumps or tussocks restricted to the shrub interspaces. Western wheatgrass may be more uniformly distributed within the shrub interspaces, occurring as widely scattered, low-vigor individual plants. Greasewood can increase the salts beneath its canopy by the uptake and concentration of salts in its leaves and the subsequent deposition of litter (Eddleman and Romo, 1987, Romo and Eddleman, 1985). This mechanism may reinforce greasewood dominance by suppressing competing plant seedlings.
Diagnosis: Shrubs are dominant. Grass cover is variable ranging from extremely sparse (greasewood dominated) to patchy with frequent large bare areas present. Soil sealing is common in shrub interspaces. Evidence of erosion such as pedestalling of plants, litter dams, elongated water flow patterns, and rills may be common, especially on areas with slopes >3%.
Submodel
Description
Gullied State: Accelerated erosion and gully formation characterize this state. Greasewood, big sagebrush, or saltbush species are the dominant vegetation. Herbaceous cover is sparse, occurring as small patches or widely spaced individual plants occupying shrub interspaces and consist of western wheatgrass, alkali sacaton, galleta, annual grasses, and forbs.
Diagnosis: Gullying is extensive and may become deep enough to restrict vehicle and livestock movement. Grass cover is sparse, and litter is confined to shrub bases or other obstructions to overland flow. Soil sealing is widespread and occupies most shrub interspaces.
Submodel
Mechanism
Transition to Shrub-Dominated (T1A) Soil drying due to blocked or redirected flow of run-on water may favor deeper-rooted shrubs and initiate the transition to the Shrub-Dominated State. Additionally, loss of grass cover due to overgrazing and drought in conjunction with the decreased competition for resources resulting from grass loss favors shrub dominance. Loss of grass cover reduces organic matter and may result in soil sealing and reduced infiltration. Soil sealing can lead to the accumulation of s alts on the soil surface and inhibit herbaceous seedling establishment.
Key indicators of approach to transition:
--The decrease of cool-season grasses
--The formation of widely spaced rings or tussocks of alkali sacaton
--Increase in size and frequency of bare patches
--Increase in amount of shrub seedlings
Mechanism
Restoration Pathway to Reference State (R2A) If shrub dominance is due to soil drying, moving or rerouting obstructions or diversions to overland flow may be necessary to restore natural run-on flow patterns. Brush control is necessary to reduce the competitive influence of shrubs and reestablish grass dominance. However, greasewood is difficult to control. It is resistant to fire (Rickard and McShane, 1984) and can re-sprout following mechanical and chemical treatment (Cluff et.al, 1983, Mueggler and Steward, 1980). Seeding salt-tolerant grasses may be necessary. The use of livestock or mechanical means to break up physical crusts and improve infiltration may enhance seeding success.
Mechanism
Transition to Gullied State (2) The continued loss of grass cover in conjunction with soil sealing, increased overland flow, and resulting erosion can cause the transition to the Gullied state. The continued loss of grass cover may be due to extended drought, overgrazing, and the competitive influence of shrubs for available soil moisture. The loss of organic matter and high salt content may increase soil susceptibility to crust formation especially on finer textured soils (USDA, Natural Resources Conservation Service. 2001). Decreased infiltration and increased flow rates due to grass cover loss and soil crusting facilitate erosion and gully formation. This state may not occur on all landscape positions. Those sites that are nearly level or are on depositional landforms may not be prone to erosion and gullying.
Key indicators of approach to transition:
--Decrease in amount of grass cover
--Increase in size and frequency of bare patches and surface crusting
--Increase in amount of rills and presence of small gullies
Mechanism
Restoration Pathway to Reference State (R3A). Erosion control such as shaping and filling gullies or installing grade stabilization structures will be necessary to restore hydrology. Brush control will be needed to reduce the competitive influence of shrubs and restore grasses. Seeding will be required to reestablish grass dominance. Rest from grazing followed by prescribed grazing will help ensure grass establishment following seeding. The multiple practices required to drive the transition back to the Reference State are costly, and chances for successful grass establishment are dependent on the degree of soil degradation and adequate precipitation following seeding.
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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.