Semi-desert Shallow Loam (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 the familiarity of rangeland relict areas where they exist. The Reference State would have been characterized by varying amounts of Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and associated herb species. Phases would vary from herb-dominated (1.1) to shrub dominated (1.3) depending mainly on how long it had been since the last wildfire. Wildfire (1.3a, 1.2b) would have reset the successional clock back to an herb-dominated community (1.1). Over the course of an approximately a 30 to 40 year fire free period, through natural succession (1.1a), the site would have first developed into near equal coverage of brush and herbaceous components (1.2), but eventually (1.2a) Wyoming sagebrush would have ultimately become more dominant (1.3). The primary grasses would have included bluebunch wheatgrass (Pseudoroegneria spicata), Western wheatgrass (Pascopyrum smithii), Indian ricegrass (Achnatherum hymenoides), and needle and thread (Hesperostipa comata). Forbs would have included a mixture of buckwheat (Eriogonum spp.), tapertip hawksbeard (Crepis acuminata), stemless mock goldenweed (Stenotus acaulis), spiny phlox (Phlox hoodii), and granite prickly phlox (Linanthus pungens), among others. 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.

Submodel

Description

State 2 is similar to State 1, 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 after the first few decades of Euro-American settlement, and can be regarded as the current potential. The irreversible historic changes and heavy growing season livestock utilization depleted the native perennial understory allowing the shrubs to thicken and dominate the site. A small component of introduced non-native species has now become part of the understory. Where cattle and horses were abundant (2.2a), the grasses were depleted (2.1), but with the later shift to sheep (2.1a), the forbs declined (2.2). Where combined grazing took place (2.1c), the shrubs continued to expand at the expense of both forbs and grasses (2.3). Lack of wildfire also served to allow increasing dominance of Wyoming big sagebrush, to the detriment of the herbs (2.1b, 2.2c). The stability of this State is maintained by a healthy, productive, and diverse plant community that can provide native seed sources and promotes soil stability, water infiltration, and soil moisture retention. The resiliency of this State will be maintained by a reduction in livestock grazing, especially during the growing season of desirable herbs. Conversely, continued heavy livestock grazing, especially during the growing season of desirable herbs, will negatively impact the resiliency of this State.

Submodel

Description

The Wyoming Big Sagebrush Super-dominance State is characterized by very dense Wyoming big sagebrush and an understory much depleted of its native herbaceous understory. Some introduced non-native species such as cheatgrass (Bromus tectorum) are present. This State is maintained by an abundant seed source for Wyoming big sagebrush, the lack of a healthy, productive and diverse herb component capable of providing native seed source, soil stabilization, and soil moisture retention, and also by lack of fire. Continued heavy grazing, particularly during the growing season of perennial herbs, will reduce the resiliency of this State; lighter grazing will allow for the State to remain resistant to change.

Submodel

Description

Exotic annuals may come to dominate the site if brush removal treatments take place during an extreme dry period, treatments are not provided adequate time to rest post-treatment, and subsequent grazing is light. The fire return interval is dramatically shortened compared to previous states, and many areas may also experience accelerated soil erosion (4.1a) which further contributes to the spiral of degradation. The stability of this State is maintained by recurrent fire and by soil erosion.

Submodel

Description

Crested wheatgrass (5.1) will be found on sites where it has been planted to provide a higher level of productivity or to control soil erosion. 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