Natural Resources
Conservation Service
Ecological site R052XY702MT
Clayey (Cy) Dry Shrubland
Last updated: 7/02/2019
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 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: Xeromorphic Woodland, Scrub and Herb Vegetation Class (3)
• Subclass: Cool Semi-Desert Scrub and Grassland Subclass (3.B)
• Formation: Cool Semi-Desert Scrub and Grassland Formation (3.B.1)
• Division: Cool Semi-Desert Scrub and Grassland Division (3.B.1.Ne)
• Macrogroup: Artemisia tridentata - Artemisia tripartita ssp. tripartita - Purshia tridentata Steppe and Shrubland Macrogroup (3.B.1.Ne.3)
• Group: Artemisia tridentata - Artemisia tripartita - Purshia tridentata Big Sagebrush Steppe and Shrubland Group (3.B.1.Ne.3.b)
• Alliance: Artemisia tridentata ssp. wyomingensis Mesic Steppe and Shrubland Alliance
• Association: Artemisia tridentata ssp. wyomingensis / Pascopyrum smithii 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. Onsite evaluations are necessary, particularly in boundary or intergrade areas where ecological sites from multiple climate zones may overlap. Clayey Dry Shrubland is a moderately extensive ecological occurring on most landscapes throughout MLRA 52. It occurs on till plains, lake plains, and low hills where slopes are less than 15 percent. This site can be found on any slope shape, but concave or linear is most common.
The distinguishing characteristic of this site is that it contains greater than 35 percent, but not more than 45 percent, clay in the upper 4 inches of soil. Soils for this ecological site are typically moderately deep to very deep (more than 20 inches to bedrock) and derived from shale residuum, clayey till, or glaciofluvial deposits. Soil surface textures (0 to 4 inches) are typically clay, clay loam, silty clay, or silty clay loam, and the soils typically have an ochric epipedon. This site is typically nonacid, with pH values greater than 5.6 throughout the soil profile. Characteristic vegetation is western wheatgrass (Pascopyrum smithii), green needlegrass (Nassella viridula), and Wyoming big sagebrush (Artemisia tridentata subsp. Wyomingensis).
Preliminary studies indicate that there may also be an acid variant of this site. This variant appears to exhibit retarded shrub growth, reduced cover of cool-season bunchgrasses, and increased cover of creeping juniper and prairie sandreed. At this time, this variant cannot be consistently identified as a separate ecological site concept and further investigation is required.
Associated sites
R052XY712MT |
Loamy (Lo) Dry Shrubland Loamy Dry Shrubland occupies similar landscapes and slope positions as Clayey Dry Shrubland, but occurs in areas where clay content is 35 percent or less. |
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R052XY703MT |
Clayey-Steep (Cystp) Dry Shrubland Clayey Steep Dry Shrubland is found adjacent to Clayey Dry Shrubland on slopes of 15 percent or greater. It typically occupies a backslope position downslope from the Clayey Dry Shrubland ecological site. |
R052XY724MT |
Shallow Clay (Swc) Dry Shrubland Shallow Clay Dry Shrubland is found adjacent to Clayey Dry Shrubland where bedrock occurs near the soil surface. It typically occupies a backslope position downslope from the Clayey Dry Shrubland ecological site. |
Similar sites
R052XY001MT |
Clayey (Cy) Dry Grassland This site differs from the Clayey Dry Shrubland in that it has slightly cooler annual temperatures and supports silver sagebrush rather than Wyoming big sagebrush. |
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R052XY712MT |
Loamy (Lo) Dry Shrubland This site differs from the Clayey Dry Shrubland in that its soils contain 35 percent or less clay in the surface 4 inches; whereas, the Clayey Dry Shrubland ecological site soils contain more than 35 percent clay in the surface 4 inches. |
R052XY703MT |
Clayey-Steep (Cystp) Dry Shrubland This site differs from the Clayey Dry Shrubland in that it is on slopes of 15 percent or greater; whereas, the Clayey Dry Shrubland ecological site is on slopes of less than 15 percent. |
R052XY724MT |
Shallow Clay (Swc) Dry Shrubland This site differs from Clayey Dry Shrubland in that depth to bedrock or paralithic bedrock is less than 20 inches. |
Table 1. Dominant plant species
Tree |
Not specified |
---|---|
Shrub |
Not specified |
Herbaceous |
Not specified |
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