Ecological site group description

Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.

Physiography

This group of ecological sites occur on alluvial fans, fan terraces, pediments, valley flats, hills, stream terraces, and structural benches at elevations between 3,700 and 6,800 feet. Slopes typically range from 2 to 15%, but can be as high as 50%. Flooding ranges from none to very rare and duration is very brief.

Climate

The climate is characterized by hot summers and cool winters. Large fluctuations in daily temperatures are common. Approximately 65–70% of moisture occurs as rain from March through October. On the average, April, May, and June are the driest months and August, September, and October are the wettest months. Precipitation is extremely variable from month to month and from year to year but averages between 6-12 inches. Much of the precipitation occurs as convection thunderstorms.

Soil features

The soils are moderately deep to very deep and well drained. Surface textures are loam, sandy loam, sandy clay loam, or silty clay loam. Rock fragments may or may not occur on the soil surface, ranging from 0 to 50 percent cover. Subsurface textures range from sandy loam to silty clay loam with 0 to more than 50 percent rock fragments. These soils formed in eolian deposits, alluvium, slope alluvium, or colluvium from sedimentary and igneous rocks. The soils are typically slightly saline. Available water-holding capacity ranges from 2 to 7 inches in the upper 40 inches of the soil. Soil moisture regime is typic aridic or ustic aridic and soil temperature regime is mesic.

Vegetation dynamics

These sites plant species composition is generally dominated by James' galleta and shadscale. Torrey's tea, snakeweed, prickly pear and yellow rabbitbrush are common shrubs, and Indian ricegrass, blue grama, mesa dropseed, and sand dropseed are common grasses. Bud sagebrush is found the more gravelly and cobbly sites. Some sites closer to washes are dominated by alkali sacaton with varying proportions of greasewood and rubber rabbitbrush.

These ecological sites have been grazed by domestic livestock since they were first introduced into the area around 1860. The common season of use is winter. These sites are resistant in that use. However, improper grazing may stress the plants and allow nutrients to become available for invasive species to flourish; as may other modern disturbances such as recreation and OHV use.

There is no evidence that these sites historically burned on a regular basis due to very large and persistent gaps between plants. However, areas that have been invaded by annuals have increased fine fuel loads and may make fire more prevalent. Cheatgrass, Russian thistle and halogeton have all been documented on these sites.

Major Land Resource Area

MLRA 035X
Colorado Plateau

Subclasses

• R035XY101UT–Desert Alkali Sandy Loam (Alkali Sacaton)
• R035XY109UT–Desert Loam (Shadscale)
• R035XY136UT–Desert Stony Loam (Shadscale-Bud Sagebrush)
• R035XY242UT–Semidesert Gravelly Loam (Shadscale)

Correlated Map Unit Components

22966787, 22966908, 22966909, 22966759, 22966957, 22966956, 22966848, 22966873, 22966840, 22966877, 22967044, 22963633, 22963726, 22963649

Stage

Provisional

Contributors

Vic Parslow
Keith Crossland
Curtis Talbot