Natural Resources
Conservation Service
Ecological site R046XC603MT
Saline Upland (SU) RRU 46-C 15-19 PZ
Last updated: 9/07/2023
Accessed: 12/22/2024
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
Major Land Resource Area (MLRA): 046X–Northern Rocky Mountain Foothills
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, three Land Resource Units (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 1981 m) however the elevations on the fringes of this MLRA may fall outside of that range in extremely small isolated areas where the boundaries between neighboring MLRAs are not easily defined. Annual precipitation ranges from 8 inches (254 mm) to, in very isolated areas, 42 inches (1083 mm). In general precipitation rarely exceeds 24 inches (610 mm). 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 46s 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 subdominance 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, common snowberry, 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.
LRU notes
LRU C is generally located in Central Montana. It borders the Little Belt Mountains, Highwood Mountains, Snowy Mountains (Big and Little), Crazy Mountains, and Castle Mountains. Included in this LRU are the foothills of the island mountain groups of the Bear’s Paw and Little Rocky Mountains. This LRU borders MLRAs 43B, 52 and 58. LRU C is the second largest of the LRUs located in Montana occupying approximately 2.6 million acres. Cities and towns located in this LRU includes Stanford, Lewistown, Grass Range, and Harlowton. Elevation ranges from 2880 feet (878 m) to 6783 feet (2068 m).
The geology is sedimentary in nature with the majority including the Colorado Shale Formation, Kootenai Formation (mixed sedimentary), Mississippian Formation (carbonatic sedimentary), terrace deposits (alluvium), Tertiary mixed sedimentary. Areas of the Claggett Formation (mudstone), Devonian (carbonatic sedimentary) as well as intrusive and extruvise volcanics (mixed) exist in the foothills of the island mountains. Landforms include hillslopes, drainage ways, fan remnants, valleys, and escarpments.
This LRU is dominated by deep, well drained soils. Soil depth is mixed with 45 percent moderately-deep, 45 percent very deep, and 10 percent other soil depth. Slopes are most frequently 0 to 15 percent and 15 to 30 percent, while higher sloping areas (30-45 percent) exist along the Little Belt and Highwood interfaces. Slightly Acid to Moderately Alkaline soils throughout. Small areas of Moderately Acid soils exist in places, in particular around Highwoods. Vast differences in soil texture within LRU exist likely due to the variation in parent material.
The climate of this LRU is classic to the MLRA concept. The precipitation falls primarily as rain in the spring however areas may receive high amounts of snowfall (i.e. Lewistown). Precipitation ranges are from 13.7 inches (348 mm) to a rare 37.4 inches (942 mm) with 18 inches as an average. This LRU has an average air temperature of 44°F (6.75 degrees C) with a range of 38 degrees Fahrenheit (3.38 degrees C) to 47.3 degrees Fahrenheit (8.52 degrees C). Frost free days tends to be one of the longest of the Montana LRUs with a range of 70 to 130 days. Soil moisture regime is Ustic with a Frigid soil temperature regime. Due to the variability in climate of this LRU, climatic subsets will be necessary to accurately describe the ecological processes.
Major watersheds within this LRU include Big Spring Creek, Judith River, Swimming Woman Creek, and Musselshell River. These watersheds provide irrigation water for production of small grains and hay. As these watersheds leave the neighboring MLRA 43B, these river systems offer fishing and other recreational opportunities.
Cropland conversion is the largest land conversion within this LRU. Small grains such as wheat and barley are the most common particularly in Judith Basin County. Conversion to recreational property is becoming a more frequent occurrence, particularly near Lewistown.
Ecological site concept
Site does not receive additional effective moisture
Soil is saline or saline sodic within surface 20 inches
No columnar structure present in soil
Site is dominated by salt tolerant plants
Associated sites
R046XC602MT |
Dense Clay (DC) RRU 46-C 15-19 PZ Site is typically lower on the landscape below Saline Upland |
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Similar sites
R046XC508MT |
Silty (Si) RRU 46-C 13-19 PZ Silty site shares a similar state and transition model with similar plants. Silty site has higher production |
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Table 1. Dominant plant species
Tree |
Not specified |
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Shrub |
(1) Sarcobatus vermiculatus |
Herbaceous |
(1) Pseudoroegneria spicata |
Click on box and path labels to scroll to the respective text.
Ecosystem states
T1 | - | Transition is triggered by long term overgrazing or other human disturbances. Long term drought or altered hydrologic function is also a factor. |
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T3 | - | Invasion of the community by nonnative herbaceous species, often as a result of long term overgrazing or intense fire which reduces vigor of native herbaceous species. |
R1 | - | Improved grazing management with favorable growing conditions may allow deep rooted bunchgrasses to reestablish dominance. Limited prescribed fire may reduce vigor of short grasses and shrubs temporarily. |
T2 | - | Invasion of the community by nonnative herbaceous species, often as a result of long term overgrazing or intense fire which reduces vigor of native herbaceous species. |
State 1 submodel, plant communities
1.1a | - | The driver for community shift 1.1A is improper grazing management or prolonged drought. This shift is triggered by the loss of vigor of tall grasses, soil erosion, or prolonged drought coupled with improper grazing. |
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1.2a | - | Proper grazing management and appropriate grazing intensity with favorable moisture conditions will facilitate or accelerate this transition. The driver is increased vigor of the tall grasses resulting in increase biomass production and dominance of plant community. The trigger for this shift is the change in grazing management favoring basin wildrye. |