Natural Resources
Conservation Service
Ecological site R053AY718MT
Slough (Sl)
Last updated: 11/22/2023
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): 053A–Northern Dark Brown Glaciated Plains
The Northern Dark Brown Glaciated Plains, MLRA 53A, is a large, agriculturally and ecologically significant area. It consists of approximately 6.1 million acres and stretches 140 miles from east to west and 120 miles from north to south, encompassing portions of 8 counties in northeastern Montana and northwestern North Dakota. This region represents part of the southern edge of the Laurentide Ice Sheet during maximum glaciation. It is one of the driest and westernmost areas within the vast network of glacially derived prairie pothole landforms of the Northern Great Plains and falls roughly between the Missouri Coteau to the east and the Brown Glaciated Plains to the west. Elevation ranges from 1,800 feet (550 meters) to 3,300 feet (1,005 meters).
Soils are primarily Mollisols, but Inceptisols and Entisols 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 (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 in glacial outwash channels and along major drainages, including portions of the Missouri, Poplar, and Big Muddy Rivers. Large eolian deposits of sand occur in the vicinity of the ancestral Missouri River channel east of Medicine Lake (Fullerton et al., 2004). The northwestern portion of the MLRA contains a large unglaciated area containing paleoterraces and large deposits of sand and gravel known as the Flaxville gravel.
Much of this MLRA was glaciated towards the end of the Wisconsin age, and the maximum glacial extent occurred approximately 20,000 years ago (Fullerton and Colton, 1986; Fullerton et al., 2004). Subsequent erosion from major stream and river systems has created numerous drainageways throughout much of the MLRA. The result is a geologically young landscape that is predominantly a dissected till plain interspersed with alluvial deposits and dominated by soils in the Mollisol and Inceptisol orders. Much of this area is typic ustic, making these soils very productive and generally well suited to production agriculture.
Dryland farming is the predominant land use, and approximately 50 percent of the land area is used for cultivated crops. Winter, spring, and durum varieties of wheat are the major crops, with over 48 million bushels produced annually (USDA-NASS, 2017). Areas of rangeland typically are on steep hillslopes along drainages. The rangeland is mostly native mixed-grass prairie similar to the Stipa-Agropyron, Stipa-Bouteloua-Agropyron, and Stipa-Bouteloua faciations (Coupland, 1950, 1961). Cool-season grasses dominate and include rhizomatous wheatgrasses, needle and thread, western porcupine grass, and green needlegrass. Woody species are generally rare; however, many of the steeper drainages support stands of trees and shrubs, such as green ash and chokecherry. Seasonally ponded, prairie pothole wetlands may occur throughout the MLRA, but the greatest concentrations are in the east and northeast where receding glaciers stagnated and formed disintegration moraines with hummocky topography and numerous areas of poorly drained soils.
Classification relationships
NRCS Soil Geography Hierarchy
• Land Resource Region: Northern Great Plains
• Major Land Resource Area (MLRA): 053A Northern Dark Brown Glaciated Plains
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: Glaciated Northern Grasslands Section 331L
• Subsection: Glaciated Northern Grasslands Subsection 331La
• Landtype association/Landtype phase: N/A
National Vegetation Classification Standard (Federal Geographic Data Committee, 2008)
• Class: Mesomorphic Shrub and Herb Vegetation Class (2)
• Subclass: Shrub and Herb Wetland Subclass (2.C)
• Formation: Temperate to Polar Freshwater Marsh, Wet Meadow and Shrubland (2.C.4)
• Division: Eastern North American Temperate & Boreal Freshwater Marsh, Wet Meadow and Shrubland (2.C.4.Nd)
• Macrogroup: Great Plains Marsh, Wet Meadow, Shrubland & Playa (2.C.4.Nd.5)
• Group: Typha spp. - Schoenoplectus americanus - Scolochloa festucacea Great Plains Freshwater Marsh (2.C.4.Nd.5.a)
EPA Ecoregions
• Level 1: Great Plains (9)
• Level 2: West-Central Semi-Arid Prairies (9.3)
• Level 3: Northwestern Glaciated Plains (42)
• Level 4: Glaciated Dark Brown Prairie (42i)
Glaciated Northern Grasslands (42j)
USFWS (Cowardin et al., 1979)
• Palustrine Persistent Emergent Semi-Permanently Flooded
Montana Riparian and Wetland Sites (Hansen et. al, 1995)
• Hardstem Bulrush Habitat Type
• Common Cattail Habitat Type
Ecological site concept
Slough is a common ecological site occurring in oxbows, relic channels, and open depressions. The distinguishing characteristics of this site are that it is located on floodplains, has a seasonal high water table less than 24 inches from the soil surface, and contains hydric soils. Soils for this ecological site are typically very deep (more than 60 inches), poorly drained, and derived from alluvium. Characteristic vegetation is broadleaf cattail (Typha latifolia), hardstem bulrush (Schoenoplectus acutus), and spikerush (Eleocharis spp.).
Associated sites
R053AY712MT |
Riparian Woodland (RW) The Riparian Woodland ecological site is adjacent to the Slough ecological site, usually on the higher terraces where hydrophytic vegetation is not present. The site is dominated by woody species. |
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R053AY719MT |
Subirrigated (Sb) The Subirrigated ecological site is adjacent to the Slough ecological site, usually on higher positions where groundwater is 24 to 40 inches from the surface. The site is dominated by facultative wetland species. |
R053AY709MT |
Overflow (Ov) The Overflow ecological site is adjacent to the Slough ecological site, usually on the highest terraces where flooding is rare or occasional and hydrophytic vegetation is not present. |
Similar sites
R053AY719MT |
Subirrigated (Sb) The Subirrigated ecological site differs from the Slough ecological site, in that it occurs on higher landscape positions. Depth to a water table is 24 to 40 inches. Obligate wetland species are rare and the site is dominated by facultative wetland species. |
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R053AY711MT |
Recharge Closed Depression (CdR) The Recharge Closed Depression ecological site differs from the Slough ecological site, in that it receives its moisture primarily from surface runoff rather than groundwater discharge. It is in closed depressions on uplands rather than on floodplains. Hydroperiods are much shorter and deep marsh vegetation is rare or absent. |
R053AY703MT |
Discharge Closed Depression (CdD) The Discharge Closed Depression ecological site differs from the Slough ecological site, in that it occurs in closed depressions on uplands rather than on floodplains. Hydroperiods are much shorter and deep marsh vegetation is rare or absent. |
Table 1. Dominant plant species
Tree |
Not specified |
---|---|
Shrub |
Not specified |
Herbaceous |
(1) Typha latifolia |
Click on box and path labels to scroll to the respective text.
Ecosystem states
T1A | - | Introduction of non-native species (creeping bentgrass, Kentucky bluegrass, etc.) |
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T2A | - | Displacement of reference species by invasive species (reed canarygrass, noxious weeds, etc.) |
T2B | - | Alteration of hydrology by dams, dikes, irrigation, etc. |
R4A | - | Restoration of natural hydrology and species diversity (labor intensive and costly, may be unfeasible in some cases) |
T4B | - | Displacement of reference species by invasive species (reed canarygrass, noxious weeds, etc.) |
State 1 submodel, plant communities
P1.1a | - | 2 or more years of average precipitation |
---|---|---|
P1.2a | - | Drought |
P1.2b | - | 2 or more years of above average precipitation |
P1.3a | - | 2 or more years of average precipitation |
State 2 submodel, plant communities
P2.1a | - | 2 or more years of average precipitation |
---|---|---|
P2.2a | - | Drought |
P2.2b | - | 2 or more years of above average precipitation |
P2.3a | - | 2 or more years of average precipitation |