Sandy (Sy) Wind River Basin Rim

Description

Bunchgrass/Sagebrush State (State 1 - Reference) is characterized by the following key species: 10% or less composition by cover of Wyoming big sagebrush, with Needleandthread (15-30% composition), Indian ricegrass, and isolated areas of western wheatgrass and prairie sandreed. Minor component to the overall composition is made up of prairie junegrass, bottlebrush squirreltail, prairie sandreed, sand dropseed, threeawns, blue grama, and threadleaf sedge. Bluebunch wheatgrass is highlighted as a key species in the historic range site documentation, but is not found to be prevalent within the Wind River Basin.

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Description

Extended periods of drought across much of the Wind River Basin (as well as most of Wyoming) has taken a toll on many communities. Persistence of drought and/or frequent over use of the grasses leads to a decline of the herbaceous species, creating the Wyoming Big Sagebrush and Bare Ground state. Wyoming big sagebrush creates a zone of protection for herbaceous understory to persist and maintain vigor in difficult conditions, providing shade, moisture reserves, and protection from herbivory. This state can be exacerbated by insects and other human disturbances. The total woody canopy cover does not necessarily increase with this community, but the percent composition by cover and production is influenced by the decrease of herbaceous vegetation and the relative stability of the woody species production, creating the appearance of increased canopy cover of sagebrush.

Risk of wildfire is minimal due to the lack of fine fuels within the understory, but the canopy of the woody vegetation can easily carry a fire under specific weather conditions. Depending on the prescription of use, trailing and other erosional patterns are highly visible in this state. The loose or coarser texture of these soils allows for increased wind scour and drifting/mounding to occur with more open ground between canopy “patches”, that further hinders fire movement.

Protection from wildfire and use, on a long-term perspective, can aid in the transition of a reference community (1.1 or 1.2) to this state as sagebrush becomes dense and decadent reducing the ability for the herbaceous component to maintain vigor. The loss of herbaceous cover leads to increased bare ground and sagebrush cover. As the site continues to weaken, the sagebrush cover is susceptible to attack by insects, disease, and old age; which can remove it from the system increasing the risk of invasion or transition to a more degraded state. The level of variability of species in this state (State 2) remains abundant, however, only one well defined community will be provided, with discussion of transitions or variances from this community.

The overall arid nature of coarse textured soils exacerbates the impact of drought and reduces the resilience and resistance of this site during extended dry periods. Yucca’s presence on this site is not frequent, but when it does occur, it can easily become a concern, especially if grazed in the winter frequently. Its growth habits produce pedestalling and drift/scour patterns on the landscape.

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Description

Blue grama and threadleaf sedge are the dominant sod-forming grasses/grass-likes that currently exist within this LRU. Both species are a native component of the reference community. The general tendency is for these species to increase with prolonged drought or under grazing pressure, becoming dominant. As the dominant species, they alter the hydrology of the site by increasing the surface runoff from the dense shallow root system that inhibits the movement of water through and funnels surface flow around the edge of the “clump”, concentrating flow into channel like patterns, creating a drier environment for native grass species and forbs to persist.

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Description

Cheatgrass or downy brome (Bromus tectorum) has quickly become the greatest threat to much of the rangelands across the west, including Wyoming. This annual invader has an aggressive growth habit that creates a hostile environment for most native species, including sagebrush. Multiple growth cycles throughout a year leaves a thick litter (duff) layer and builds a significant seedbank. Cheatgrass’s ability to persist through the winter under a blanket of snow and grow early allow it to take advantage of early spring precipitation and snowmelt (winter annual). Shifts in climatic patterns, changes in management, and exposure to human activity are a few of the explanations for the current flush and rapid expanse across the western United States.

Although cheatgrass is the most prevalent large scale threat for rangeland managers, a variety of thistles and knapweeds, in combination with other aggressive invaders such as whitetop (hoary cress), black henbane, field bindweed, and leafy spurge are increasing in density and frequency, producing their own set of challenging management issues. As more species are found or as other species become more prevalent on a large scale, the community dynamics in this state will shift in response to the concerns of the identified species.

This state is characterized by the presence (not necessarily the dominance) of invasive/non-native species. Extended periods of drought alone or in combination with over utilization, insect damage or wildfire has weakened the native composition of the community opening the canopy for invasion. The competitive nature of annuals and other invasive species, creates a complex environment that inhibits control, and makes it implausible to attain complete eradication once an invasive species has established on the landscape.

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Description

Lack of season long, dependable water sources for irrigation has limited the cultivation use of this landscape. Isolated areas along the lower edge of the rim may have limited access for irrigation, but the larger land use (excluding livestock) is energy development and wildlife/recreation. The broken nature of the rim provides more topographic relief for movement of wild game, yet access is still easy to moderate for wheeled traffic. Although the disturbance footprints within this LRU are smaller scale, old homestead locations, abandoned crop fields, and energy development has left their mark.

Disturbance to these highly erodible soils (whether it was mechanical, cultural, or natural), changes soil structure, hydrologic function, and possibly stability. The loss of resilience or resistance to support native vegetation or the ability to respond to management the same as an undisturbed site, occurs as these factors are changed (structure, hydrology, stability). Reclamation or restoration of an area will not replace the original function and factors that made the original location respond as it did. So these "altered" lands may, after significant inputs and time, look similar to the Reference communities (1.1 or 1.2), but they will not be able to respond/function as the Reference community will.

This state can be achieved with one disturbance of any state or community within the State and Transition Model or diagram. Once the site has experienced an event that has altered the soil properties (erosional, depositional, hydrological or chemical), the site potential is altered. The soils have not been altered to the extent that they are outside the site characteristics, but the potential has shifted enough that it is no longer truly comparable to the reference state. Location or site specific investigation may need to occur to determine if a disturbed/reclaimed area still meets site characteristics.

To illustrate this concept, visualize an area that was impacted by drought removing the native grasses leaving a dense and decadent stand of Wyoming big sagebrush. A few weak (low vigor) needleandthread and blue grama plants persist within the crown of the sagebrush, but are not able to repopulate the area in a reasonable time. The landowner decides to seed the site using a small rototiller behind a tractor to prepare small areas within the sagebrush to broadcast a native seed mix. He then hand-raked the seed and used a roller barrel to compact the seedbed. The species selection he used was an assortment of native grass seed collected from neighboring sites. The tillage was minimal, but broke up the structure of the soil, mixing the loose surface with the blocky and slightly heavier subsurface. The change is reflected in the available water capacity of the soil, increasing infiltration slightly, but creating a limitation in permeability with the “plow pan”. The exposure to air, dries the mixed zone rapidly, wicking salts and carbonates to the surface that were otherwise not prevalent in the soil. The site is prone to erosion during the establishment period, and experiences soil movement.

The time required to allow the re-development of structure and the cryptogrammic crust, as well as any impact to chemistry, is beyond the natural function of management. The initial flush of vegetation is kochia and Russian thistle and mustards, a successional plant community. So the site begins its own recovery, but the time required to return to the original conditions (pre-disturbance) is outside of feasible consideration. The site, however, may become similar in composition to reference, but the integrity of the soil is altered, changing potential of the site.

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