General information

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.

MLRA notes

Major Land Resource Area (MLRA): 046X–Northern and Central Rocky Mountain Foothills

The Provisional ESD Initiative was established to expedite the development of ecological site descriptions through the development of provisional ESDs. While Provisional ESDs are not complete, the intent is to produce an ESD complete enough for land managers to use while approved ESDs are being developed. This project area has mixed ownership falling primarily under private ownership or lands managed by the Blackfeet Nation. This PES project is contained within MLRA 46.
Major Land Resource Area (MLRA) 46, Rocky Mountain Foothills, is approximately 11.6 million acres. MLRA 46’s extent has changed over recent years and is now primarily located in Montana and Wyoming with limited acres in Utah and Colorado. It spans from the Canadian border south to the Uinta Mountains of Northwest Colorado. MLRA 46 is a transitional MLRA between the plains and mountains of primarily non-forested rangeland. In Montana, 3 LRUs exist based on differences in geology, landscape, soils, water resources, and plant communities. Elevations for this MLRA in Montana vary from a low of 3200 to 6500 feet (975 to 1981m) however the elevations on the fringes of this MLRA may fall outside of that range in extremely small isolated areas where the boundaries between LRU C and MLRA 43B LRU G are not easily defined. Annual precipitation ranges from 8 inches (254mm) to, in very isolated areas, 42 inches (1083mm). In general precipitation rarely exceeds 24 inches (610mm). Frost-free days are variable from 50 days near the Crazy and Beartooth Mountains to 130 days in the foothills south of the Bear’s Paw Mountains of Central Montana. The geology of MLRA 46 is generally Cretaceous and Jurassic marine sediments.
MLRA 46’s plant communities are dominated by cool-season bunchgrasses with mixed shrubs. This MLRA is rarely forested; however, ponderosa and limber pine do occupy areas. Portions of this MRLA may have a sub dominance of warm-season mid-statured bunchgrasses like little bluestem, however the general concept of the MLRA does not have a large component of warm-season species. Wyoming big sagebrush, mountain big sagebrush, silver sagebrush, and shrubby cinquefoil tend to be the dominant shrub component. The kind and presences of shrubs tends to be driven by a combination of soils and climate. Due to the variable nature of the Land Resources Units, climatic subsets will be necessary to describe the ecological sites and the variation of plant communities for this MLRA.
The Rocky Mountain Front Foothills LRU is the northernmost LRU of MLRA 46. The boundaries are the Canadian border to the north, the Rocky Mountain Front LRU of MLRA 43B and the western extent of Continental Glaciation (MLRA 52).
The Rocky Mountain Front Foothills LRU’s geology is generally sedimentary in nature. Primary geological units include Two Medicine Limestone & Sandstone, Colorado Shale, Glacial Drift (alluvium), Terrace deposits (alluvium) and St Mary River formation (mudstone). Landforms include outwash terraces, escarpments, fan remnants, valleys, hillslopes, and drainage ways. Elevations of this landscape is from 3221 feet (982 m) to 6954 feet (2120 m).
Well drained soils are dominate in this LRU. Most areas have 0 to 15 percent slope, while some are 15 to 30 percent mostly on the 43B boundary. Soils are slight to moderate alkaline, except for small area next to mountains. Mean clay percentages are mostly above 23 percent. Primarily very deep soils 70 percent, moderately-deep and deep soils 30 percent.
The climate of this LRU is the most variable of MLRA 46’s LRUs however the average of 16.9 inches (429mm) follows the typical MLRA concept. The major difference between this LRU and the others of MLRA 46 is the Chinook wind. These winds create massive temperature swings in the winter which can melt snow cover and initiate bud growth on shrubs. These changes may dry soil affecting plant production and species composition. The Rocky Mountain Front Foothills receives 10 inches (247 mm) to 42 inches (1083 mm) annually. The average air temperature ranges from 36 degrees F (2.39 degrees C) to 46 degrees F (8.02 degrees C). The soil temperature regime is frigid with a soil moisture regime dominated by ustic with areas of udic. Frost-free days is from 70 to 100 days.
The vegetation potential for the Rocky Mountain Front Foothills LRU can be variable but is dominated by rangeland. Forested extents are typically minimal and consist primarily of limber pine, ponderosa pine, and Rocky Mountain juniper with mixed grassland. The rangeland of this LRU follows the general concept of the MLRA. The dryer sites are dominated by bluebunch wheatgrass and as the precipitation increases and temperatures decrease rough fescue increase. In areas that receive the highest precipitation, Richardson’s needlegrass may exist. Shrub cover is limited in this area and is generally silver sagebrush and shrubby cinquefoil with areas of chokecherry and buffaloberry (both russet and silver). The glacial drift areas will often have wetland associated vegetation as well as large areas of quaking aspen.

Ecological site concept

• This site occurs in flood plains of perennial and intermittent streams, near springs and seeps, or other areas having a permanent or perched water table with riparian area
• Dominant Cover: mixed vegetation
• Site receives additional water
• Moisture Regime: ustic
• Temperature Regime: frigid to cry
• Elevation Range: 3800-5800
• Soils are
o Not saline or saline-sodic
o Moderately deep, deep, or very deep
o Typically less than 5% stone and boulder cover (<10% max)
• Seasonal high water table within 40” (approx. 100cm) of soil surface.
• Transitional area of foothills separating plains and mountains
• Parent material is recent alluvium
• Slope: 0-5%

Associated sites

Similar sites

Table 1. Dominant plant species