Semi-desert Gravel (Bluebunch wheatgrass/ Wyoming big sagebrush)

Description

The Reference State is a description of this ecological site just prior to Euro-American settlement but long after the arrival of Native Americans. The description of the Reference State was determined by NRCS Soil Survey Type Site Location information and familiarity with rangeland relict areas where they exist. Before Euro-American settlement, this would have been a moderately vegetated variant of semi-desert sagebrush with about 60 percent of the forage production from grasses, 15 percent forbs, and 15 percent woody plants, primarily from Wyoming big sagebrush (Artemisia tridentata spp. wyomingensis). The productivity would have been relatively higher than nearby non-gravelly (e.g. R034AY2ggUT Semi-desert Loam Ecological Site) because of the Inverse Texture Principle (Noy-Meir, 1973). In deserts and semi-deserts, finer textured soils are effectively drier and thus typically have lower production potential than coarser textured soils. The major grasses would have included a caespitose form of bluebunch wheatgrass (Pseudoroegneria spicata), slender wheatgrass (Elymus trachycaulus), Western wheatgrass (Pascopyrum smithii), Indian ricegrass (Achnatherum hymenoides), and needle-and-thread (Hesperostipa comata). Other grasses and grass-likes would have included prairie junegrass (Koeleria macrantha), bottlebrush squirreltail (Elymus elymoides), Sandberg bluegrass (Poa secunda), and thickspike wheatgrass (Elymus lanceolatus). Other associated woody species may have included yellow rabbitbrush (Chrysothamnus viscidiflorus), black sagebrush (Artemisia nova), and winterfat (Krascheninnikovia lanata). A more complete list of species by lifeform for the Reference State is available in the accompanying tables in the “Plant Community Composition by Weight and Percentage” section of this document. Total annual forage production of these sites would have averaged approximately 400 to 700 pounds per acre. The fire return interval would have averaged approximately 20 to 25 years. The phases of this ESD would have depended on the time since last fire, starting with a bluebunch wheatgrass-dominated site (1.1) immediately following fire (1.3a, 1.2b), with yellow rabbitbrush becoming temporarily dominant 5 to 15 years post-fire (1.1a), followed by return to Wyoming big sagebrush dominance with a bunchgrass understory (1.3) 15 to 20 years post-fire (1.2a).

Submodel

Description

State 2 is very similar to State 1 in form and function, with the exception of the presence of non-native plants and animals, possible extinctions of native species, and a different climate. State 2 is a description of the ecological site immediately following Euro-American settlement, and is considered the current potential for this site. The phases of this State vary between a bluebunch wheatgrass dominated phase (2.1), to a yellow rabbitbrush/ Wyoming big sagebrush invaded phase (2.2), to a Wyoming big sagebrush with bluebunch wheatgrass understory phase (2.3), which develop according to the time since last wildfire (2.3a or 2.2b, 2.1a, 2.2a, respectively). This State is maintained by periodic wildfire, which reduces the sagebrush component, and a productive understory capable of providing a seed source for native herbaceous species. The resiliency of this state is reduced by lack of occasional wildfire and loss of native seed source. Moderate levels of growing-season livestock utilization will allow this State to maintain its resiliency, but excessive levels of growing-season livestock utilization will reduce its resiliency.

Submodel

Description

The plant community that characterizes this state is a tall, dense stand of Wyoming big sagebrush with a diminished understory. The Wyoming big sagebrush will remain super-dominant as wildfire continues to be suppressed, and with heavy unrestricted grazing of livestock. The chance of wildfire has diminished due to lack of fine fuels. This State is maintained by the continuation of fire suppression and heavy livestock grazing.

Submodel

Description

It is possible to see a reduction in the super-dominance of sagebrush through prescribed grazing using sheep in fall months or, alternatively, following an outbreak of Aroga moth. Sheep will focus on sagebrush when no other forage is available, and Aroga moths are capable of killing off large stands of sagebrush. Reducing the sagebrush dominance could allow the native perennial grasses and forbs to re-establish in the following spring (4.1). While there has been some invasion of exotics, such as the mustards (primarily Descurainia spp. and Sisymbrium altissimun) and cheatgrass (Bromus tectorum) in this State, the examples of where they occur in Rich County are only for short periods of time unless the disturbance is continuous. This is because the Wasatch Formation from which these soils are derived had their nutrients depleted when subtropical forests of the Miocene occupied these parent materials. Persisting dominance of invasives such as cheatgrass, require the higher planes of soil nutrients available from younger, less-leached parent materials. This State can be maintained by deferring growing-season grazing in some years, but a return to intense growing-season grazing will reduce the resiliency of this State.

Submodel

Description

Crested wheatgrass (5.1) will be found on sites where it has been planted to provide a higher level of productivity. To keep the shrubs from re-invading, it may be necessary to follow up with additional chemical or mechanical treatment (5.1a). This resiliency of this State can be maintained by moderate livestock grazing, but excessive livestock grazing will reduce its resiliency.

Submodel