Natural Resources
Conservation Service
Ecological site R052XY721MT
Sandy (Sy) Dry Shrubland
Last updated: 7/03/2019
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.
Figure 1. Mapped extent
Areas shown in blue indicate the maximum mapped extent of this ecological site. Other ecological sites likely occur within the highlighted areas. It is also possible for this ecological site to occur outside of highlighted areas if detailed soil survey has not been completed or recently updated.
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 sedimentary bedrock largely consisting of Cretaceous shale, sandstone, and mudstone (Vuke et al., 2007) 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, with the maximum glacial extent occurring 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 the 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 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 yet fully understood.
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 in the fact that 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 Shrubland
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 and Shrubland Formation (2.B.2)
• Division: Andropogon gerardii - Pascopyrum smithii - Bouteloua gracilis Grassland and Shrubland Division (2.B.2.Nb)
• Macrogroup: Andropogon hallii - Calamovilfa longifolia - Artemisia filifolia Great Plains Sand Grassland and Shrubland Macrogroup (2.B.2.Nb.4)
• Group: Artemisia filifolia / Calamovilfa longifolia - Yucca glauca Sand Shrubland Group (2.B.2.Nb.4.a)
• Alliance: Yucca glauca Prairie Scrub Alliance
• Association: Yucca glauca / Calamovilfa longifolia Shrub Grassland
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 Shrubland 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. Sandy Dry Shrubland is a moderately extensive ecological site on till plain landscapes in MLRA 52. This ecological site occurs on kames, eskers, outwash fans, and terraces. Slopes are typically less than 25 percent but may be steeper in some areas. This site can occur on any slope shape or slope position.
The distinguishing characteristics of this site are coarse-loamy textures in the upper 4 inches of soil and a relatively undeveloped soil profile. Calcium carbonate (lime) concentration in the upper 5 inches of soil varies from 0 to 15 percent but is typically 5 percent or less. Soils are typically moderately deep to very deep (more than 20 inches to bedrock) and are primarily derived from glaciofluvial material or alluvium over glacial till. In dissected areas where bedrock is exposed this site can be formed in soft sandstone. Soils in some areas, but not all, have a mollic epipedon. Soil surface textures fall within the coarse-loamy textural family and have less than 18 percent clay and less than 70 percent sand. Underlying horizons commonly have a cambic horizon that exhibits minimal pedogenic development. Species composition is dominated by drought-tolerant plants with deep, extensive root systems. Production potential on this site is typically somewhat less than on a loamy soil due to the reduced available water-holding capacity (AWC). Characteristic vegetation is needle and thread (Hesperostipa comata), threadleaf sedge (Carex filifolia), prairie sandreed (Calamovilfa longifolia), and Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis).
Associated sites
R052XY712MT |
Loamy (Lo) Dry Shrubland This site occurs adjacent to the Sandy Dry Shrubland ecological site. It generally occurs on similar landscape positions, but occupies areas with finer textured soils such as ground moraines rather than kames or eskers. |
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R052XY710MT |
Limy (Ly) Dry Shrubland This site occurs adjacent to the Sandy Dry Shrubland ecological site on similar landscapes. It is generally in positions with a convex slope shape; and in areas of finer textured soils such as ground moraines rather than kames or eskers. |
R052XY714MT |
Loamy-Steep (Lostp) Dry Shrubland This site occurs on moderate to steeply sloping hillslopes adjacent to or downslope from the Sandy Dry Shrubland ecological site. It is generally in backslope positions with a linear or concave slope shape and in areas of finer textured soils. |
Similar sites
R052XY712MT |
Loamy (Lo) Dry Shrubland This site differs from the Sandy Dry Shrubland ecological site in that soils contain more than 18 percent clay in the upper 4 inches. Western wheatgrass is a predominant component of the plant community. |
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R052XY710MT |
Limy (Ly) Dry Shrubland This site differs from the Sandy Dry Shrubland ecological site in that soils contain more than 18 percent clay in the upper 4 inches and have greater than 5 percent calcium carbonate in the upper 5 inches (evidenced by strong or violet effervescence). Prairie sandreed does not occur on this site. |
R052XY110MT |
Sandy (Sy) Dry Grassland This site differs from the Sandy Dry Shrubland ecological site in that it has slightly cooler annual temperatures and supports silver sagebrush rather than big sagebrush. |
Table 1. Dominant plant species
Tree |
Not specified |
---|---|
Shrub |
Not specified |
Herbaceous |
Not specified |
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