Semi-desert Loamy Run-on (Basin big sagebrush/ Mixed bunchgrass)

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. Pre-settlement fire return intervals of 20 to 30 years tended to favor the native bunchgrasses. Under such conditions, the native plant community would have been characterized by mixed bunchgrasses and basin big sagebrush (Artemisia tridentata ssp. tridentata) (2.1). The major grasses would have included basin wildrye (Leymus cinereus), rhizomatous bluebunch wheatgrass (Pseudoroegneria spicata), bottlebrush squirreltail (Elymus elymoides), native bluegrasses (Poa secunda, Poa fendleriana), and thickspike wheatgrass (Elymus lanceolatus). Other associated woody species may have included yellow rabbitbrush (Chrysothamnus viscidiflorus) 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.

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 shortly following Euro-American settlement. This State can be regarded as the current potential. The range in plant communities within this State is characterized by the relative amount of bunchgrass present, which is primarily associated with the time since last fire. With more recent fires and prescribed grazing (2.2a) the plant community would be dominated by mixed bunchgrasses and basin big sagebrush (2.1). In the absence of fire and with protection from livestock grazing (2.1a), the plant community would shift to a more basin big sagebrush dominated site, but would still have remnants of the native bunchgrass understory (2.2).

Resiliency of this State is maintained by the availability of native seed sources for both the mixed bunchgrasses and basin big sagebrush, and by wildfire. This site responds well to cool season fire and more moderate non-growing season grazing regimes provided that the seed sources for the mixed bunchgrasses are present. A pre-settlement fire return interval of 20-30 years favored the grasses. Without fire, bunchgrass diversity and production may diminish, while sagebrush may increase and ultimately outcompete the native bunchgrasses. This shift in plant community composition puts this State at greater risk in the event of a hot summer or fall fire; further degradation could occur if grazing were to be initiated immediately following such a fire. Hotter fires followed by heavy grazing could cause the replacement of the basin big sagebrush component with fire-tolerant species such as yellow rabbitbrush and rhizomatous wheatgrasses.

Submodel

Description

State 3: Basin Big Sagebrush/ Rhizomatous Wheatgrass State
Sites where heavy continuous season-long grazing has taken place in the absence of fire will develop into a basin big sagebrush-dominated plant community accompanied by rhizomatous bluebunch and western wheatgrasses. Resiliency of this State is maintained by the absence of fire and heavy grazing during the growing season for grasses, which removes grazing-intolerant grass species (bunchgrasses) and leaves only grazing-tolerant grasses and sagebrush. The dominance of basin big sagebrush and lack of native bunchgrasses places this State at risk in the event of a hot summer or fall fire.

Submodel

Description

Yellow rabbitbrush and rhizomatous wheatgrass will be found on sites that have experienced both heavy continuous season-long grazing and frequent wildfire disturbances. This is the most commonly found current State. The resiliency of this State is maintained by the ability of root-sprouting species (yellow rabbitbrush and rhizomatous wheatgrasses) to successfully establish after fire and out-compete other fire and grazing-intolerant species.

Submodel