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 ecological site group occurs on alluvial fans, fan remnants, plateaus, structural benches, terraces, talus slopes, escarpments, landslides, hillslopes, mountain slopes, and ledges. Run off is medium to very high (due to the steep slopes). Slopes typically range from 2-80%. Flatter slopes may occur in some locations. Elevations ranges from 3700-7500 feet.

Climate

The climate is characterized by hot summers and cool to warm winters. Large fluctuations in daily temperatures are common. Average annual precipitation is 7 to 13 inches. Approximately 70 percent of the precipitation occurs as rain from March through October. On the average, February, 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. Much of the summer precipitation occurs as convection thunderstorms.

Soil features

The characteristic soils in this site range from moderately deep to very deep and are well drained. They formed in alluvium, slope alluvium, colluvium and residuum derived mainly from sandstone, shale, and igneous rocks. Soils are loamy-skeletal with more than 50 percent rock fragments throughout the soil profile. The soil surface rock fragment cover ranges from very gravelly to extremely bouldery. Water holding capacity ranges from 2 to 5 inches of water in the upper 40 inches of soil. Soils are nonsaline to very slightly saline. The soil moisture regime is aridic or ustic aridic and the soil temperature regime is mesic.

Vegetation dynamics

Typically, blackbrush forms the dominant visual aspect of this group. Mormon tea, fourwing saltbush, shadscale, and winterfat commonly occur. Indian ricegrass and James galleta are the major herbaceous species.

The natural disturbance regime consisted of infrequent fires with a fire return interval of 35 to 100 + years on the less sloping sites to only spotty occurrences on the steeper and bouldery sites. Blackbrush appears to act as a paleo-endemic species and once removed, may not able to reestablish itself.

The more accessible ecological sites have been grazed by domestic livestock since they were first introduced into the area. This livestock introduction, with its the use of fencing and the development of reliable water sources influenced the disturbance regime historically associated with these ecological sites. Improperly managed livestock grazing, where it occurred, may have caused these sites to depart from the reference plant community. Continued improper domestic livestock grazing likely removed the native perennial grasses and palatable shrubs from the system which created opportunities for invasive plants to establish. Cheatgrass, red brome, and Russian thistle are the non-native species most likely to invade.

Major Land Resource Area

MLRA 035X
Colorado Plateau

Subclasses

• R035XY139UT–Desert Stony Loam (Blackbrush)
• R035XY203UT–Semidesert Bouldery Fan (Blackbrush)
• R035XY243UT–Semidesert Stony Loam (Blackbrush)

Correlated Map Unit Components

22592500, 22593802, 22594349, 22593809, 22594351, 22593818, 22594107, 22595008, 22594834, 22594836, 22598347, 22597935, 22963637, 22963623, 22963441

Stage

Provisional

Contributors

Vic Parslow
Keith Crossland
Curtis Talbot