Limy Upland (LiU) Big Horn Basin Rim

Description

The Reference State holds a healthy mix of bluebunch wheatgrass, rhizomatous wheatgrasses, as well as Indian ricegrass, needle and thread, and to a minor extent sod-formers such as blue grama and threadleaf sedge.

The high calcium carbonates in the soils reduces the differences between coarser textured soils to finer textured soils. A minor shift between Indian ricegrass, blue grama and threadleaf sedge to needle and thread, western wheatgrass, and bottlebrush squirreltail does occur between sandier textures to clay loam textures. The lack of significant distinction limits the ability to separate the two communities into individual ecological sites, so the range of plant composition will capture this characteristic within the plant community tables.

Characteristics and indicators

The reference state is characterized by the dominance of bluebunch wheatgrass, at 50% or less composition by weight, with Wyoming big sagebrush at 10% or less composition by weight. The droughty nature of these soils reduces the plant cover and maintains a higher level of bare ground than a soil with no chemistry. Lichen is a common soil cover that is found to indicate elevated levels of carbonates in the soil.

Resilience management

Although bluebunch wheatgrass and sagebrush are resilient species, they are at-risk when subjected to continuous season-long or year-long grazing. Once they are removed from a community they can be difficult to recover.

Submodel

Description

Blue grama and threadleaf sedge are sod-forming species that exist as a component of the perennial vegetation naturally (in reference communities) in the ecological site. The general tendency of these species is to increase under grazing pressure, becoming dominant. The species that gains dominance appears to be dependent on which species is more prevalent in the community before the negative pressures are applied.

Characteristics and indicators

This state is characterized by the dominance of these sod-formers and the lack of a most other cool-season bunchgrasses is distinct on the landscape. The lack of sagebrush and increasing cactus cover is also characteristic of the Sod-Former State (State 2).

Resilience management

Sod-forming species, blue-grama and threadleaf sedge alike, are hardy and resilient. Once they have established a dense root-mat they are extremely difficult to remove from a site without significant inputs. They also alter the natural hydrologic process of a community limiting the potential for other species to recover.

Submodel

Description

If continued pressure or disturbance occurs on the vulnerable community within the reference state (State 1), it can be forced into the Sagebrush/Bare Ground State. Over time, drought or grazing pressures on this state will reduce the herbaceous plant cover to occurrences under the canopy of Wyoming Big sagebrush or similar shrub species (rabbitbrush) and within the protection of prickly pear cactus.

Characteristics and indicators

A sagebrush canopy with limited understory cover is the major characteristic of this community. There is a misnomer that claimed an increase in brush cover, however, the lack of understory will give the perception of increased shrub cover.

Resilience management

The soil conditions are limiting for plant establishment, and the climatic variables within this area are also challenging. Once the understory is reduced, it will take time and resources to improve the site. The existing understory species will have an influence on the recovery potential of a community.

A Wyoming big sagebrush community with a scare understory of bottlebrush squirreltail was located. There were trace amounts of bluebunch wheatgrass, Sandberg bluegrass, and annual forbs. Production was low and Wyoming big sagebrush was at approximately 25% canopy. Bureau of Land Management (BLM), completed a variety of treatments over three years. The trials showed that the timing and climate during the trial determined which species would thrive. The mowing treatments during this trial occurred at optimal germination conditions for bottlebrush squirreltail. So the mowing treatment acted as a seed dispersal process allowing the plant species to flourish.

Submodel

Description

Invasive plant species are a permanent concern with rangelands and management. Each year new species are discovered and will alter this section as they are. Currently within the Big Horn Basin there are several varieties of thistles, knapweeds, milkweeds, mustards and others that create a management issue for livestock and ecology. In areas where there has been a disturbance, natural or man-made, these species can gain a place in the landscape and are difficult to impossible to eradicate. Because of this it becomes a battle to maintain control with annual or prolonged management of the weed species, and preventing further shifts or changes to the native composition.

Submodel

Description

The Degraded state could be drafted as a stand-alone box within the state and transition model diagram. No matter what state a site originally is ranked in, once the site is mechanically disturbed, or suffers a catastrophic or significant natural disaster that alters 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 site has not been altered out of the current site, but the potential has shifted enough that it is no longer truly comparable to the reference community. So a dynamic state was captured to detail the altered communities that exist on the landscape.

Submodel