Natural Resources
Conservation Service
Ecological site R052XY716MT
Panspot (Pn) 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: 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 ssp. wyomingensis - Artemisia tridentata ssp. tridentata Steppe and Shrubland Group (3.B.1.Ne.3.a)
• Alliance: Artemisia tridentata ssp. wyomingensis Dry Steppe and Shrubland Alliance
• 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 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. Panspot Dry Shrubland is a somewhat extensive ecological site occurring on till plains, moraines, and fans in MLRA 52. This ecological site is especially prevalent on the Malta sublobe in Blaine and Phillips Counties where glacial till is underlain by the Bearpaw Shale Formation. This site is typically associated with Loamy, Panspot, and Thin Claypan ecological sites.
The distinguishing characteristic of this site is the presence of a dense, sodium-affected (natric) horizon at a depth of 1 inch or less from the soil surface. The natric horizon exhibits columnar structure, is very hard, and severely limits both root penetration and infiltration. Soils are typically moderately deep to very deep (greater than 20 inches to bedrock), derived from glacial till, and occur on slopes of less than 8 percent. Soil surface textures (0 to 4 inches) are very fine sandy loam to loam, and the natric horizon is clay or clay loam. Deep-rooted plant species are not well adapted to this site due to the shallow depth of the natric horizon. Species composition is dominated by shallow-rooted short-statured species. Rhizomatous species are subdominant while deep-rooted bunchgrasses are generally absent. Characteristic vegetation is blue grama (Bouteloua gracilis), Sandberg bluegrass (Poa secunda), and western wheatgrass (Pascopyrum smithii).The principal shrub on this site is Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis).
Associated sites
R052XY712MT |
Loamy (Lo) Dry Shrubland This site occupies similar landscapes to the Panspot Dry Shrubland ecological site. In the natric soils complex, the Loamy Dry Shrubland ecological site is typically found on the highest micro-topography; whereas, the Panspot Dry Shrubland ecological site occupies the lowest positions. |
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R052XY731MT |
Thin Claypan (Tcp) Dry Shrubland This site occupies similar landscapes to the Panspot Dry Shrubland ecological site. In the natric soils complex, the Thin Claypan Dry Shrubland ecological site is typically found in mid-level micro-topography, higher than Panspot Dry Shrubland ecological site, but lower than the Claypan and the Loamy Dry Shrubland ecological sites. |
R052XY704MT |
Claypan (Cp) Dry Shrubland This site occupies similar landscapes to the Panspot Dry Shrubland ecological site. In the natric soils complex, the Claypan Dry Shrubland ecological site is typically found in mid-level micro-topography, higher than Panspot and Thin Claypan Dry Shrubland ecological sites, but lower than the Loamy Dry Shrubland ecological site. |
Similar sites
R052XY145MT |
Panspot (Pn) Dry Grassland This site differs from the Panspot Dry Shrubland ecological site 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 Panspot Dry Shrubland ecological site in that the root restricting layer (evidenced by columnar structure) is either absent or greater than 10 inches below the soil surface. Deep-rooted bunchgrasses are a major component of the plant community. |
R052XY731MT |
Thin Claypan (Tcp) Dry Shrubland This site differs from the Panspot Dry Shrubland ecological site in that the root-restricting layer (evidenced by columnar structure) is greater than 1 inch to 4 inches below the soil surface. Deep-rooted bunchgrasses are rare or absent. |
R052XY704MT |
Claypan (Cp) Dry Shrubland This site differs from the Panspot Dry Shrubland ecological site in that the root-restricting layer (evidenced by columnar structure) is greater than 4 inches to 10 inches below the soil surface. Deep-rooted bunchgrasses comprise approximately 10 percent of the plant community. |
Figure 2. Figure 3. Similar and Associated Sites Diagram. Figure 3 shows an example of a landscape cross section with a natric catena.
Table 1. Dominant plant species
Tree |
Not specified |
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Shrub |
Not specified |
Herbaceous |
Not specified |
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