Loamy Bottom

Description

The reference state contains plant communities presumed to occur prior to the introduction of nonnative plants, livestock grazing, and other modern disturbances. Basin big sagebrush dominance depends on time since fire, insect outbreak or extended drought. In both communities the grasses are the dominant component.

It is a very diverse community with 10-20 or more species present throughout the site. This diversity adds to a site’s stability. Often, decreasing diversity can be one of the first indicators of site deterioration. Key species that indicate a pristine and functioning system include. Species that often act as increasers with disturbance and indicate a deteriorating site include: basin big sagebrush, white sagebrush, squirreltail, foxtail barley, broom snakeweed, and rabbitbrush. This site has less than 20% big sagebrush canopy cover. The percentage of shrubs in this state will fluctuate depending on frequency and intensity of disturbances such as fire, or grazing. Typically the sage brush increases until fire is introduced to the system. Following the fire, rabbitbrush and annual forbs will increase creating a rabbitbrush phase that will be phased out as perennial grasses and sagebrush reestablish themselves.

The following is from the 1982 range site:

If ecological retrogression is cattle-induced, desirable grass species will decrease. However, if retrogression is sheep-induced, desirable forbs, shrubs and grasses will be reduced. Deterioration of the site due to overgrazing by cattle will decrease western wheatgrass, muttongrass, Indian ricegrass, New Mexico feathergrass, and bottlebrush squirreltail. Further deterioration by overgrazing will increase basin big sagebrush, rabitbrush, broom snakeweed, plains prickly pear and foxtail barley. With severe depletion of the natural grasses, species such as cheatgrass, Russian thistle, Italian cocklebur, and 5-stem tamarisk will invade the site.

Submodel

Description

The current potential state is similar to the reference state, however invasive species are present in all community phases. This state is generally dominated by big sagebrush, however depending on disturbance history, native grasses, forbs, or other shrubs may dominate the site. Primary disturbance mechanisms include fire, native herbivore grazing, insect outbreak, domestic livestock grazing and surface disturbances, (i.e. road and pipeline development and off road vehicle (OHV) use). Timing of these disturbances dictates the ecological dynamics that occur. The current potential state is self-sustaining; but is losing resistance to change due to lower resistance to disturbances and lower resilience following disturbances. When disturbances occur, the rate of recovery is variable depending on severity.
The current potential state is similar in structure and function to the reference state, however invasive and non-natives species are present in all community phases. The current potential state is generally dominated by perennial grasses.

Submodel

Description

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 the majority production. The depleted understory state occurs when perennial grasses have been lost from the understory. Perennial forbs may also be reduced. This state is may not be capable of carrying a stand replacing fire that removes big sagebrush due to a reduction in fine fuels. If improper grazing continues to occur shrubs will continue to increase and perennial grasses will begin to be replaced by annuals such as cheatgrass.
The hydrologic function of this community is still intact throughout the entirety of the bottom. Meaning, there is no bench or entrenched/incised channel. The water has access to the entirety of the bottom 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 current potential 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. This state may return to the current potential state through prescribed fire or brush management by chemical or mechanical means followed by reseeding.

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 bottom 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 bottom 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 bottom more rapidly in a shorter period of time. These minor changes in the microclimate, especially on the periphery of the bottom, are enough to allow for the sagebrush to continue advancing into the bottom 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 bottom and begins to form a channel. As the water becomes more channelized, the bottom becomes even less capable of dissipating the energy and channelization increases moving down the system and a head-cut start moving up the system.

This state has two fluctuating phases. Both phases have an entrenched channel where water has no access to the bottom floodplain and although vegetation in the channel may return to a community similar to the current potential (if not a little wetter), the majority of the bottom 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 current potential community with some exception. Since there is the same amount of water consolidated to a smaller area, 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

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 bottom and not the bottom of the channel.

Submodel