Loamy (Ly) Wind River Basin Core

Description

Mid-stature Cool-season Grasses/Sagebrush State (State 1 - Reference) is characterized by the key species including: 15% or less composition by cover of Wyoming big sagebrush, with rhizomatous wheatgrasses (western and thickspike) (<30%), needleandthread, Indian ricegrass, and isolated areas of bluebunch wheatgrass. Minor component to the overall composition is made up of Sandberg bluegrass, bottlebrush squirreltail, prairie junegrass, blue grama, and threadleaf sedge.

Submodel

Description

Wyoming big sagebrush creates a niche for most herbaceous understory to persist and maintain some vigor in difficult conditions by utilizing the moisture and shelter provided by the canopy as well as protection from grazing. Persistence of drought and/or frequent over use by livestock and/or wildlife leads to a decline of the herbaceous species, creating the Wyoming Big Sagebrush and Bare Ground State. This state can be exacerbated by insects and other human disturbances. The total woody canopy cover does not necessarily always increase with this community, but the percent composition by cover and production is swayed by the decrease of herbaceous vegetation and the relative stability of production by the woody species, creating the appearance of increased canopy by sagebrush.

Risk of wildfire within this state 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 certain climatic conditions. Depending on the prescription of use, trailing and other erosional patterns are highly visible in this state.

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; leading to a high amount of bare ground and sagebrush cover. As the herbaceous cover declines and the site continues to weaken, the sagebrush cover is susceptible to attack by insects, disease, and general old age that can remove it from the system creating a system that is at risk of invasion or transition to a more degraded state. There is a high level of variability of species in this State, which will shift in response to precipitation or in response to past management. Only one well defined community will be provided, with discussion of transitions or variances from this community.

Submodel

Description

The dominant sod-forming grass that currently exists within this LRU is blue grama with intermixed areas of threadleaf sedge. Both are species that persist as a component of the perennial vegetation naturally (in reference communities) within the ecological site. The general tendency is for these species to increase with prolonged drought or under grazing pressure, becoming dominant. Hydrology of the site is altered by increased surface runoff from the dense shallow root system that inhibits the movement of water through the soil. The sod patches will direct surface flow around the edge of the mat concentrating flow into channel like patterns, creating a difficult or hostile environment for native grass species and forbs to persist.

The mechanisms to transition this state back to State 1 or State 2 requires mechanical and chemical processes to break up the sod and allow/encourage the mid-stature cool-season grasses. Many times, a seed source is not sufficient to allow this to occur so seeding may be required to produce the restoration pathway. No successful restorations have occurred with native species, so has not been described below.

Submodel

Description

Cheatgrass or Downy brome (Bromus tectorum) is the invader that has the greatest concern for most land managers. This 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; the ability for this annual to persist through the winter under a blanket of snow and sprout early gives it the advantage of all early spring precipitation and snowmelt. 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 threat most prevalent to rangelands on a large scale, a variety of knapweeds (namely spotted and Russian) and whitetop (hoary cress) are increasing in density and frequency, producing their own set of challenging management issues. As more species are found within the Basin 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 of an invasive/non-native species. Extended periods of drought alone or in combination with misuse, 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.

Submodel

Description

The transition of an Invaded/Sagebrush community into the Invaded state, is typically a result of wildfire, a failed controlled burn or other event that removes the sagebrush from the site and allows a readily available seed bank or seed source of the undesirable species to flourish. The most common community that is found in the Wind River Basin and much of the surrounding regions is Cheatgrass.

There are other threats present, such as knapweeds and whitetop, which can develop into near monoculture stands. The loss of diversity, changes to the potential of a site due to allelopathy or other deterrent characteristics of invasive species, and risks or land use capabilities associated with the various invasive species creates a hostile environment for both native species and grazers. The resilience and resistance of the invaders create a management road block that is usually financially driven. Many times, once an invasion reaches this point, many land managers have no choice but to learn to utilize what they have rather than to try to treat or improve the site, specifically in relation to cheatgrass control.

Submodel

Description

The arid nature of this region has played a major role in the development and transitions in land use over time. Landscapes accessible by irrigation water and equipment were farmed and many were later abandoned and left to return to rangeland. Other landscapes were treated with a variety of prescriptions to manage or eradicate sagebrush. Tillage of the soil, change in hydrology caused by the loss of vegetative structure, constant climatic fluctuations, and advancements in seed sources have created this altered state.

Once a soil has been disturbed, whether it was mechanical, cultural, or natural the change in soil structure, hydrologic function, and possibly stability prevent a site from supporting the native vegetation or responding to management the same as an undisturbed site. 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.

The Disturbed or degraded state could be drafted as a stand-alone box within the state and transition model diagram. No matter what state a location is classified, once the site has experience an event that has altered the soil properties (erosional, depositional, hydrological or chemical), the site potential is altered. To consider this as an alternate ecological site would not be unreasonable. In some cases (site by site consideration), a re-correlation of a location may be the best solution. But in many cases, the soils have not been altered out of the current site characteristics, but the potential has shifted enough that it is no longer truly comparable to the reference state.

The extent and type of soil disturbance as well as the species selection used to revegetate the site determine the extent of alterations that limit this site. Even in the case of minimal tillage or ground disturbance, the surface crust and cryptogrammic crusts are displaced or destroyed altering the infiltration and nutrient flow within the soil (degradation of the biota within the soil).

The loss of soil structure changes the holding capacity of the soil, removing the argillic or clay bulge, increasing the movement through the soil, and reducing the water holding capacity. The time required for soil to rebuild structure, biological crusts to regrow on the site, and the impact to chemistry and plant variety are highly variable depending on the climatic conditions following the event.

The initial flush of vegetation following a disturbance is kochia. Russian thistle and mustards. Although they are only successional species, they provide organic material, nutrient flow and erosional protection; however, they lack the perennial structure and root system to fully stabilize the site. When the seeded section establishes, the site may become similar in composition to reference, but the integrity of the soil is altered, changing potential of the site. So a dynamic state was captured to detail the altered communities that exist on the landscape.

Submodel