Loamy Calcareous (LyCa) Big Horn Basin Rim

Description

The reference state is characterized by the dominance of Wyoming big sagebrush, at 15% or less composition by weight, with Bluebunch wheatgrass, at 40% or less composition by weight. But with these two dominant species, the site holds a healthy mix of rhizomatous wheatgrass, Western and Thickspike, as well as Indian ricegrass, Needleandthread, and to a minor extent sod-formers such as Threadleaf sedge and Blue grama.

In refining the ecological site characteristics and the reference state, the reference was made to soils that classified as fine-loamy in comparison to coarse loamy soil texture classification and how the plant communities varied. The initial thought was that these two classifications needed to be separated. As a review of the specific locations where this was visible on the landscape, a phenomenon on the landscape was documented showing a plant community shift as soil surface structure changes.

A rangeland trend plot study site has two differing plant communities occurring alternating along a transect. Both communities are within the reference state, but at separate ends of the plant composition spectrum. One community was expressing a higher occurrence of Indian ricegrass, Threadleaf sedge and Blue grama (coarse-loamy) while the second plant community was expressing a higher composition of Western wheatgrass and Needleandthread (fine-loamy). The transitions appeared to be abrupt in nature between these plant communities.

Soils were reviewed, and found no apparent difference in the soil profile excluding the surface horizon or cap. Under the Indian ricegrass community, the soil surface has granular structure, where the Western wheatgrass community soils have a thin vesicular crust or platy structure. Beyond this minimal surface difference there appeared to be no difference in soil structure, texture, or classification.

The lack of distinction limits the ability to separate the two communities into individual ecological sites or communities, but the range of plant composition will capture this characteristic within the plant community tables. The photo documenting the occurrence of this phenomenon is in the photo for Community 1.2, demonstrates these two plant communities as they co-exist on the landscape.

Submodel

Description

During the late 1960’s and throughout current time, there have been large areas of sagebrush control completed using techniques such as aerial applied chemicals, burning, mowing, spike treatments and other land based hand treatments. Many of the treatments today are done on a smaller scale, mosaic pattern to better benefit wildlife, however, some of the older style treatments were used to eradicate large areas of sagebrush in one prescription.

Prescribed grazing or possibly long-term prescribed grazing, will allow recovery of this plant community to a community similar to the Reference state if there is relict or nearby seed source for sagebrush species. The process may take several years or may need mechanical, localized plantings to assist the process. The use of drought recovery plans are essential to the success of re-introducing shrub species once they are removed due to the already altered hydrologic function of the site. Again, the process will be slow and the probability of recovering to the 1.1 community is marginal, but there is the ability to recover the 1.2 state with time and possibly minor mechanical improvements.

As a consequence, there are large acreages of landscape that have lost all sagebrush cover and may never recover, unless seeding or transplants are completed. The plant community, and state, created by this loss of sagebrush is dominated by the Perennial bunchgrasses and forbs as the only cover. The variability of this plant community is a reflection of the treatment that occurred and the state or condition of the landscape prior to the treatment.

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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. This state name is somewhat misleading in the perception considering that bare ground may only increase slightly and in many cases there is no change or a light decrease in cover by sagebrush. Over time, drought or grazing pressures on this state will eventually drive the sagebrush/shrub canopy out or decrease the health and vigor of the plant to a non-sustainable level. The herbaceous plant production may remain only slightly decreased, but the thriving species usually occur under the canopy of Wyoming Big sagebrush or similar shrub species (rabbitbrush) and within the protection of Prickly pear cactus.

Brush management, followed by prescribed grazing, may return this plant community to a similar or near Reference Plant Community. If prescribed fire is used as a means to reduce or remove the shrubs, sufficient fine fuels will need to be present. This may require deferment from grazing prior to treatment. Post management is critical to ensure success. This can range from two or more years of rest to partial growing season deferment, depending on the condition of the understory at the time of treatment and the growing conditions following treatment. In the case of an intense wildfire that occurs when desirable plants are not completely dormant, the length of time required to reach a community within the Reference State may be increased and seeding of natives is recommended.

A site was identified that was dominated by Wyoming big sagebrush with an understory of bottlebrush squirreltail, Bluebunch wheatgrass, Sandberg bluegrass, and annual forbs. Production was low; Wyoming big sagebrush was at approximately 25% canopy. The site was selected for a trial sagebrush treatment by Bureau of Land Management (BLM), one area was treated with small patch burns and several other areas were treated with a mowing prescription, at varying times of year and heights. The canopy of herbaceous cover for the burned site is delayed and very slow to respond, where the canopy under the mowing treatments responded within a growing season. Transects established on the location were dominated by Bottlebrush squirreltail, and minimal other species. The sites continue to be monitored. It is the consensus, that the timing and the climate for that year was optimal for the residual seed bank of Bottlebrush squirreltail. So the mowing treatment acted as a seed dispersal process allowing the plant species to flourish.

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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.

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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.

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Description

Currently within the Big Horn Basin, Cheatgrass or Downy brome (Bromus tectorum) is the invasive annual grass species that has been a concern for management. Although there are many other species of forbs that are becoming monoculture stands, Cheatgrass is the species that is taking large acres of land quickly in this region.

Knapweed, namely spotted, also became dominate in large dense stands and produces an even more challenging set of management issues. As more species are found within the Big Horn Basin or as other species become more prevalent in large scale communities, this section will need to shift to meet the concerns of these species. But with the persistence of Cheatgrass and the lack of a successful control agent at this time, it is not conceivable that Cheatgrass will ever go away or become less of a management challenge.

This state is characterized by the lack of all or most of the shrub component of this site. Whether drought or wildfire has removed this component, the competitive nature of annuals, the altered fire regime created by Cheatgrass, and the effect of the loss of the shrub component itself creates an environment that does not support the propagation of new shrubs.

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.

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