Semidesert Gravelly Sandy Loam (Black 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 with a low presence of non-native plants. The least modified plant community (1.1) within the Reference State would have been a black sagebrush-dominated (Artemisia nova) stand with scattered prickly pear (Opuntia polyacantha) and associated bunch grasses such as Indian ricegrass (Achnatherum hymenoides), needle and thread grass (Hesperostipa comata), Sandberg bluegrass (Poa secunda), muttongrass (Poa fendleriana), and bottlebrush squirreltail (Elymus elymoides). Forbs such as phlox (Phlox spp.), buckwheat (Eriogonum spp.) and locoweed (Astragalus spp.) would have been common. The generally gravelly soils would have accentuated the effects of drought and reduced the chances of fire altering this state. The reference plant community (1.1) would have been relatively stable with occasional use by wildlife. However, heavy utilization by bison, elk, and Native American horses on these sites (1.1a) would have depleted the grasses creating a near monoculture of black sagebrush (1.2). Heavy browsing by deer during the dormant season of black sagebrush (1.1b) would have created an herbaceous variant (1.3). Infestation of some insects and pathogens on sagebrush (1.1c) could have led to a similar result where the herbaceous species became temporarily dominant (1.3). The combination of an unusually dry period and heavy utilization by all grazers (e.g. deer, bison, elk, and horses used by Native Americans) (1.1d) would have removed the palatable species from the plant community while allowing unpalatable, shorter-lived species such as yellow rabbitbrush (Chrysothamnus viscidiflorus ssp. viscidiflorus), locoweed, and phlox to predominate (1.4). The depauperate black sagebrush (Artemisia nova) community (1.2) could have also shifted to the unpalatable short-lived shrub community phase (1.4) in areas that have sustained heavy browsing by deer (1.2b). Relatively rocky sites such as these typically would not have declined in overall cover or productivity. However, the portion that was palatable may have changed appreciably. Similarly, these soils would have been more resistant to erosion than other stone-free soils. Each of the phases within State 1 could have returned to Community Phase 1.1 if climate conditions were within the normal range of variability and there was a release from heavy grazing and/or browsing pressure (1.2a, 1.3a, and 1.4a). A small amount of Wyoming big sagebrush and/or an informally recognized variety of big sagebrush (A. tridentata), called “bonnevillensis” (Shultz, 2009) would have also been present. A more complete list of species by lifeform for the Reference State, Community Phase 1.1 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 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 following Euro-American settlement, which can be regarded as the current potential. The least modified plant community (2.1) within State 2 is a black sagebrush-dominated stand with scattered prickly pear and associated bunch grasses such as bluebunch wheatgrass, Indian ricegrass, Sandberg bluegrass, muttongrass, and bottlebrush squirreltail. Forbs such as phlox, buckwheat, locoweed, and common yarrow are common. The generally shallow and stony soils accentuate the effect of drought and reduce the chances of fires altering this state. This plant community is relatively stable under mixed use by wildlife and livestock. However, heavy utilization by bison, elk, horses, and domestic cattle on these sites during the growing season (2.1a) would deplete the grasses creating a near monoculture of black sagebrush (2.2). Heavy browsing by deer and sheep (2.1b) would create an herbaceous variant (2.3) because of year-round utilization of black sagebrush. Occasionally very wet years during El Nino-Southern Oscillation periods can cause temporary soil anoxia (West 2000) (2.1c) killing the sagebrush and allowing the forbs and grasses to dominate for a short time (2.3). Some insects and pathogens on sagebrush (2.1c) can lead to a similar result where the herbaceous species become temporarily dominant (2.3). The interaction of an unusually dry period and heavy utilization of grasses by bison, elk, horses, and domestic cattle (2.1d) would remove the palatable species from the plant community while allowing unpalatable, shorter-lived species such as yellow rabbitbrush, locoweed, and phlox to predominate. While species composition does not change, species abundance does (2.4). The depauperate black sagebrush community (2.2) may also shift to the unpalatable short-lived shrub community phase (2.4) with heavy utilization of browse by deer and sheep (2.2b). Relatively rocky sites such as these typically do not decline in overall cover or productivity, however, the portion that is palatable may change appreciably. Similarly, these soils are more resistant to erosion than associated stone-free soils. Each of the phases within State 2 can return to Community Phase 2.1 when climate conditions are within the normal range of variability and grazing pressure is moderated (2.2a, 2.3a, 2.4a). A small amount of Wyoming big sagebrush and/or an informally recognized variety of big sagebrush, called “bonnevillensis” (Shultz, 2009) may also be present.

Submodel