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.
Major Land Resource Area (MLRA): 070A–High Plateaus of the Southwestern Great Plains
This site is confined to the Canadian Plateaus LRU (70A.1) of MLRA 70A.
This site is confined to the Canadian Plateaus LRU (70A.1) of MLRA 70A.
Please use the following key:
1a. The site exists on a landform of volcanic origin, such as a basalt plateau, or is part of an escarpment system that rises directly to a volcanic structure. These escarpments are included if they have volcanic alluvium or colluvium (i.e. basalt, rhyolite, tuff, cinders) overlying non-volcanic residuum or bedrock (i.e. sandstone, shale). → VOLCANIC PLATEAUS LRU (VP)
User tip: Other alluvial or colluvial landform features extending below the escarpments are not included unless they have a predominance of volcanic fragments at the surface. Also, note that playas atop volcanic plateaus are included within the VP-LRU.
1b. All other sites. → 2
2a. The site exists in the annulus or floor of a playa. → CANADIAN PLATEAUS LRU (CP)
User tip: Small islands of playas occur within large areas of HP-LRU. These sites may be far from the nearest CP landform but will still key-out to the CP-LRU. The playa rim components, however, may key out to either LRU, so it is important to properly identify their soil properties.
2b All other sites. → 3
3a. The site is part of an escarpment landscape complex (defined below) or is within a canyon, valley, or small basin confined by such escarpments. At the upper boundary of the LRU, the soil surface meets at least 4 of the following 5 criteria:
I. Shallow or very shallow soils are present in at least 50% of the landform area;
II. Soils are underlain by sandstone bedrock of the Cretaceous Dakota Formation or older;
III. Presence or historical evidence of a conifer stand (≥ 2% canopy cover);
IV. The ground surface has a slope of at least 10%;
V. The landforms drain towards steep-walled escarpments or canyons below the Dakota sandstone (older Jurassic and Triassic Formations underlie this sandstone mesa cap).
→ MESOZOIC CANYONS AND BREAKS LRU (MCB)
User tip: The MCB sites also occur on any colluvial or alluvial bottomlands confined within escarpments or canyons. Some valleys transition from CP to MCB, or back to CP, and the turning point can be difficult to determine. Generally, the landforms are part of the MCB when confined between Dakota sandstone breaks or escarpments on both sides. Much of the acreage in the MCB is aproned by colluvial debris fans—composed of sandy materials with large sandstone fragments visible on the soil surface, including large stones or boulders. The soils in the bottoms of these confined valleys will also be in the MCB. When the valley opens, or there is only a single escarpment opening to the plains, the landforms below the steeper, rockier escarpments will be members of the CP-LRU.
3b. Fewer than 4 of the above criteria are met. → 4
4a. The soil is on a plateau summit position (tread) and is within 50 cm to contact with either plateau bedrock (non-soil bedrock of cemented sandstone, limestone, or shale) or strath terrace cobbles, but not a petrocalcic contact (caprock or caliche of cemented calcium carbonate). → CANADIAN PLATEAUS LRU (CP)
4b. No plateau bedrock or strath terrace cobbles within 50 cm. → 5
5a. Fragments (>2 mm) are visible within the soil profile and/or on the surface. If fragments cannot be found in the profile, it is acceptable to look nearby on ant mounds or around burrows. If site is in a drainageway, one can look for fragments on landforms immediately upslope.→ 6
5b. Fragments are entirely absent. → 7
6a. Fragments are mostly petronodes or High Plains gravels. → HIGH PLAINS LRU (HP)
6b. Fragments are mostly plateau bedrock fragments. → CANADIAN PLATEAUS LRU
7a. All horizons in the upper 100 cm of soil have textures of sandy clay loam or sandier.
→ CANADIAN PLATEAUS LRU (CP)
7b. At least one horizon in the upper 100 cm of soil has a texture that is less sandy than sandy clay loam. → HIGH PLAINS LRU (HP)
NRCS and BLM: Shallow Limy Escarpments Canadian Plateaus LRU Major Land Resource Area 70A, High Plateaus of the Southwestern Great Plains Land Resource Region G, Western Great Plains Range and Irrigated Region (United States Department of Agriculture, Natural Resources Conservation Service, 2006).
USFS: Shallow Limy Escarpments Sandy Smooth High Plains Subsection Southern High Plains Section Great Plains-Palouse Dry Steppe Province (Cleland, et al., 2007).
EPA: Shallow Limy Escarpments<26l Upper Canadian Plateau<26 Southwestern Tablelands (Griffith, et al., 2006).
Ecological site concept
The Limy Escarpments ecological site occurs on plateau escarpments in the Canadian Plateaus LRU. This LRU occupies the western portion of MLRA 70A and extends from Las Vegas, NM at the southern end to beyond Raton, NM at its northern end. Elevation for the Canadian Plateaus LRU ranges from 5,000 to 7,500 feet.
This concept covers the entire escarpment—from the shoulder position at the top to the point at which the escarpment grades into an alluvial fan apron or alluvial flat below.
Soil depth for the Limy Escarpments ranges from 4 inches (10 centimeters [cm]) to over 40 inches (100 cm) to lithic contact with limestone or paralithic contact with weathered shale. Shallow, lithic soils are typically found toward the top of the escarpment, and deeper, shale-dominated soils are found below. Slope gradient is at least 10 percent. Bedrock outcroppings should be visible in some places as small areas of exposed angular limestone benches that typically contour the slope. Where the slope inflection changes from convex to concave, at the lower part of the escarpment, alluvial fans will begin as a transition from shallow to deep soils, with some elements of both Limy Escarpments and Limy ecosites. Because of the relatively steep slope gradient, aspect has a significant effect on microclimate.
There is considerable overlap between the soils on the Limy Escarpments ecological site and soils on other sites. Additionally, soil properties vary considerably within this site depending on slope position. Thus, geomorphology and the presence of limestone rock outcrop are the most reliable indicators of this site. Unlike other steep sites in the Canadian Plateaus LRU, the Limy Escarpments provides ideal habitat for tree species on its truly lithic soils (typically found toward the top of the escarpment). This makes the lower slope positions particularly vulnerable to encroachment by trees. For this reason, the Limy Escarpments concept includes multiple soil types that are inextricable linked—much like the stream channel and floodplains of a riparian system.
Despite considerable variability in soil properties, there are some common themes. First, the soil surface is draped with a great deal of calcareous rock fragments—typically composed of limestone, and almost always covering more than half of the surface area. Second, soils react strongly or violently to dilute hydrochloric acid (HCl), indicating considerable free carbonates. The combination of free carbonates and calcareous surface fragments provides critical habitat for New Mexico feathergrass. The high concentration of surface fragments protects soils from erosion.
This site is similar to Limy Escarpments but is on slopes less than 10% and contains no shallow bedrock. Limy often occupies fans emanating from the base of Limy Escarpments. Thus, Limy Escarpments frequently contributes run-on moisture to the Limy site.
This site differs from Limy sites in that it occurs on escarpments with slopes of 10% or more, and its soils are ≤ 50 cm to bedrock. These escarpments can contribute water to Limy sites via run-on and through-flow.
This site occurs in playas. Nearby Limy Escarpments sites contribute water to this site via run-on and through-flow. Typically, there are alluvial landforms (fan remnants or alluvial flats) between escarpments and playas, so the Limy and Clayey Alluvium sites typically act as conduits between the latter.
This site occurs in soils that lack a combination of free carbonates and ≥ 5% calcareous fragments at the surface, and lack horizons with ≥ 35% clay in the upper 50 cm.
This site occurs on the channels and floodplains of ephemeral streams. Adjacent Limy Escarpment sites contribute water to this site via run-on and through-flow.
This site occurs where soils are ≤ 50 cm to lithic contact with limestone bedrock, whereas Limy sites may be shallow or have a lithic contact at some depth, but not both.
This site occurs on complex landscape of hills, mesa sides, bajada and narrow valleys. They formed in calcareous old alluvium and eolian sediments from limestone and sandstone. The slopes are usually smooth and soils are shallow to moderately deep.
This occurs on nearly level to rolling upland sites as low rounded ridges, hill slopes, mesas or as low hills (on the convex position of the landscape). Steep-sided canyons frequently dissect the landscape.These are well-drained shallow soils. The parent material or root restriction layer is at depths of 20 inches or less and is limestone or indurated caliche.
The Laporte component of the Shallow Limy Slopes is currently correlated to the Loamy site, which was designed in another MLRA.
Table 1. Dominant plant species
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