Natural Resources
Conservation Service
Ecological site R052XY094MT
Loamy Sodic (Losd) Dry Grassland
Last updated: 12/28/2022
Accessed: 11/13/2024
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): 052X–Brown Glaciated Plains
The Brown Glaciated Plains, MLRA 52, is an expansive, agriculturally and ecologically significant area. It consists of approximately 14.5 million acres and stretches across 350 miles from east to west, encompassing portions of 15 counties in north-central Montana. This region represents the southwestern limit of the Laurentide Ice Sheet and is considered to be the driest and westernmost area within the vast network of glacially derived prairie pothole landforms of the northern Great Plains. Elevation ranges from 2,000 feet (610 meters) to 4,600 feet (1,400 meters).
Soils are primarily Mollisols, but Entisols, Inceptisols, Alfisols, and Vertisols are also common. Till from continental glaciation is the predominant parent material, but alluvium and bedrock are also common. Till deposits are typically less than 50 feet thick, and in some areas glacially deformed bedrock occurs at or near the soil surface (Soller, 2001). Underlying the till is sedimentary bedrock largely consisting of Cretaceous shale, sandstone, and mudstone (Vuke et al., 2007). The bedrock is commonly exposed on hillslopes, particularly along drainageways. Significant alluvial deposits occur along glacial outwash channels and major drainages, including portions of the Missouri, Teton, Marias, Milk, and Frenchman Rivers. Large glacial lakes, particularly in the western half of the MLRA, deposited clayey and silty lacustrine sediments (Fullerton et al., 2013).
Much of the western portion of this MLRA was glaciated towards the end of the Wisconsin age, and the maximum glacial extent occurred approximately 20,000 years ago (Fullerton et al., 2004). The result is a geologically young landscape that is predominantly a level till plain interspersed with lake plains and dominated by soils in the Mollisol and Vertisol orders. These soils are very productive and generally are well suited to dryland farming. Much of this area is aridic-ustic. Crop-fallow dryland wheat farming is the predominant land use. Areas of rangeland typically are on steep hillslopes along drainages.
The rangeland, much of which is native mixedgrass prairie, increases in abundance in the eastern half of the MLRA. The Wisconsin-age till in the north-central part of this area typically formed large disintegration moraines with steep slopes and numerous poorly drained potholes. A large portion of Wisconsin-age till occurring on the type of level terrain that would typically be optimal for farming has large amounts of less-suitable sodium-affected Natrustalfs. Significant portions of Blaine, Phillips, and Valley Counties were glaciated approximately 150,000 years ago during the Illinoisan age. Due to erosion and dissection of the landscape, many of these areas have steeper slopes and more exposed bedrock than areas glaciated during the Wisconsin age (Fullerton and Colton, 1986).
While much of the rangeland in the aridic-ustic portion of MLRA 52 is classified as belonging to the “dry grassland” climatic zone, sites in portions of southern MLRA 52 may belong to the “dry shrubland” climatic zone. The dry shrubland climatic zone represents the northernmost extent of the big sagebrush (Artemisia tridentata) steppe on the Great Plains. Because similar soils occur in both southern and northern portions of the MLRA, it is currently hypothesized that climate is the primary driving factor affecting big sagebrush distribution in this area. However, the precise factors are not fully understood at this time.
Sizeable tracts of largely unbroken rangeland in the eastern half of the MLRA and adjacent southern Saskatchewan are home to the Northern Montana population of greater sage-grouse (Centrocercus urophasianus), and large portions of this area are considered to be a Priority Area for Conservation (PAC) by the U.S. Fish and Wildlife Service (U.S. Fish and Wildlife Service, 2013). This population is unique among sage grouse populations because many individuals overwinter in the big sagebrush steppe (dry shrubland) in the southern portion of the MLRA and then migrate to the northern portion of the MLRA, which lacks big sagebrush (dry grassland), to live the rest of the year (Smith, 2013).
Areas of the till plain near the Bearpaw and Highwood Mountains as well as the Sweetgrass Hills and Rocky Mountain foothills are at higher elevations, receive higher amounts of precipitation, and have a typic-ustic moisture regime. These areas have significantly more rangeland production than the drier aridic-ustic portions of the MLRA and have enough moisture to produce crops annually rather than just bi-annually, as in the drier areas. Ecological sites in this higher precipitation area are classified as the Moist Grassland climatic zone.
Classification relationships
NRCS Soil Geography Hierarchy
• Land Resource Region: Northern Great Plains
• Major Land Resource Area (MLRA): 052 Brown Glaciated Plains
• Climate Zone: Dry Grassland
National Hierarchical Framework of Ecological Units (Cleland et al., 1997; McNab et al., 2007)
• Domain: Dry
• Division: Temperate Steppe
• Province: Great Plains-Palouse Dry Steppe Province 331
• Section: Northwestern Glaciated Plains 331D
• Subsection: Montana Glaciated Plains 331Dh
• Landtype Association/Landtype Phase: N/A
National Vegetation Classification Standard (Federal Geographic Data Committee, 2008)
• Class: Mesomorphic Shrub and Herb Vegetation Class (2)
• Subclass: Temperate and Boreal Grassland and Shrubland Subclass (2.B)
• Formation: Temperate Grassland, Meadow, and Shrubland Formation (2.B.2)
• Division: Great Plains Grassland and Shrubland Division (2.b.2.Nb)
• Macrogroup: Hesperostipa comata – Pascopyrum smithii – Festuca hallii Grassland Macrogroup (2.B.2.Nb.2)
• Group: Pascopyrum smithii – Hesperostipa comata – Schizachyrium scoparium Mixedgrass Prairie Group (2.B.2.Nb.2.c)
• Alliance: No existing correlation
• Association: No existing correlation
EPA Ecoregions
• Level 1: Great Plains (9)
• Level 2: West-Central Semi-Arid Prairies (9.3)
• Level 3: Northwestern Glaciated Plains (42)
• Level 4: North-Central Brown Glaciated Plains (42o) and Glaciated Northern Grasslands (42j)
Ecological site concept
This provisional ecological site occurs in the Dry Grassland climatic zone of MLRA 52. Figure 1 illustrates the distribution of this ecological site based on current data. This map is approximate, is not intended to be definitive, and may be subject to change. Onsite evaluations are necessary, particularly in boundary or intergrade areas where ecological sites from multiple climate zones may overlap. Loamy Sodic Dry Grassland is an ecological site of limited extent occurring on alluvial landscapes throughout MLRA 52. It occurs on alluvial fans, drainageways, and terraces where salts have accumulated.
The distinguishing characteristic of this site is that soils contain less than 35 percent clay in the upper 4 inches and that saline, sodic, or saline-sodic conditions are evident in the upper 20 inches of soil. Soils for this ecological site are typically very deep (more than 60 inches) and derived from fine-loamy alluvium or outwash deposits. Soil textures in the upper 4 inches are typically loam, clay loam, silt loam, or silty clay loam. Soils typically have an ochric epipedon. Characteristic vegetation is western wheatgrass (Pascopyrum smithii) and inland saltgrass (Distichlis spicata). The principal sagebrush species on this site is silver sagebrush (Artemisia cana), which typically only occurs at low cover.
Associated sites
R052XY030MT |
Limy (Ly) Dry Grassland Limy Dry Grassland is on similar landscapes, typically it is found on higher slope positions than Loamy Sodic Dry Grassland. It occurs in areas where lime has accumulated rather than salts. |
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R052XY012MT |
Dense Clay Sodic (Dcsd) Dry Grassland Dense Clay Sodic Dry Grassland is on similar landscapes and slope positions as Loamy Sodic Dry Grassland. Typically it occurs in areas where clay content is greater than 35 percent. |
R052XY032MT |
Loamy (Lo) Dry Grassland Loamy Dry Grassland is on similar landscapes, typically it is found on higher slope positions than Loamy Sodic Dry Grassland. It occurs in areas where salts and lime have not accumulated. |
Similar sites
R052XY713MT |
Loamy Sodic (Losd) Dry Shrubland This site differs from Loamy Sodic Dry Grassland in that it has slightly warmer annual temperatures and can support Wyoming big sagebrush. |
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R052XY012MT |
Dense Clay Sodic (Dcsd) Dry Grassland This site differs from Loamy Sodic Dry Grassland in that soils contain more than 35 percent clay in the upper 4 inches. |
R052XY091MT |
Saline Overflow (Sov) This site differs from Loamy Sodic Dry Grassland in that Saline Overflow is found on floodplains and receives enough additional moisture to significantly increase production, whereas the Loamy Sodic Dry Grassland site occurs in uplands or ephemeral drainageways and does not receive enough additional moisture to increase production. |
R052XY032MT |
Loamy (Lo) Dry Grassland This site differs from Loamy Sodic Dry Grassland in that soils do not exhibit saline, sodic, or saline-sodic conditions in the upper 20 inches of the profile. This is evidenced by the lack of sodium-tolerant species, such as Nutall’s alkaligrass and inland saltgrass. |
Table 1. Dominant plant species
Tree |
Not specified |
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Shrub |
Not specified |
Herbaceous |
Not specified |
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