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 only applicable to the Canadian Plateaus LRU of MLRA 70A (LRU 70A.1).
This site is only applicable to the Canadian Plateaus LRU of MLRA 70A (LRU 70A.1). Please refer to the following key:
Land Resource Unit (LRU) Key for MLRA 70A
– High Plateaus of the Southwestern Great Plains
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: Ephemeral Drainageways 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: Ephemeral Drainageways Sandy Smooth High Plains Subsection Southern High Plains Section Great Plains-Palouse Dry Steppe Province (Cleland, et al., 2007).
EPA: Ephemeral Drainageways <26l Upper Canadian Plateau<26 Southwestern Tablelands (Griffith et al., 2006).
Ecological site concept
Landforms that collect water are important ecological refuges within semi-arid climates. In severe drought years, they can serve as critical vestiges of viable feed for foraging wildlife. And they are typically the last good opportunity to retain moisture in the local landscape during significant rain events before being lost to surface water networks. Therefore, it is important that these areas are properly recognized and conserved in as high a functioning condition as possible.
The Ephemeral Drainageways ecological site occurs on concave drainageways or swales in the Canadian Plateaus (CP) LRU. The CP 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 CP LRU ranges from 5,000 to 7,500 feet.
The central concept for the Ephemeral Drainageways site is the subtle patterns of dendritic drainages that extend across the plateaus concentrating moisture from uplands and conveying it to lower terrain. The enhanced moisture in these sites extends the period of available plant moisture during dryer periods of the growing season. The Ephemeral Drainageways site occurs in alluvial deposits in concave positions that typically have a high water holding capacity that allow them to efficiently store the extra moisture they receive. During heavy rainfall events which typically happen during intense summer storms, these intermittent drainageways act as broad channels and may experience flooding for brief periods. These sites are also important contributors to regional water table recharge.
Soil depth for the Ephemeral Drainageways is over 78 inches (200 centimeters) to root-restrictive layers. Slope gradient ranges from 0 to 5 percent causing aspect to have very little effect on site dynamics. Surface texture ranges from silty clay loam to silty clay, with some areas having sandy clay loams with mostly fine and very fine sands.
During early stages of ESD development on the CP, two ecosites were proposed for ephemeral drainageways—one with significant accumulations of moderately to highly soluble salts, and the other generally lacking salts. However, extensive reconnaissance showed saline conditions to be quite rare—occurring only where the hydrology of drainageways (or stretches thereof) has been significantly altered by the addition of irrigation water to landforms above. For example, diversion of water into a given playa to promote waterfowl habitat can lead to elevated salinity in both drainageways and playas lower on the landscape. Thus, it was deemed most appropriate to represent saline conditions as a management-induced ecological state rather than a distinct ecological site.
This site occurs on escarpments where soils are ≤ 50 cm to a root-restrictive layer, and have slopes >10%.
Playa sites may be hydrologically connected to some drainageways via subsurface-flow.
This site occurs where soils are ≤ 50 cm to lithic contact with limestone bedrock, and often supports oneseed juniper savannahs.
This site occurs on escarpments where soils are ≤ 50 cm to a root-restrictive layer, and have at least one of the following properties at the soil surface: 1) strong or violent effervescence (HCl, 1N); or 2) ≥ 5% calcareous surface fragments.
This site occurs in soils that have high clay in subsurface horizons and contribute moisture to Ephemeral Drainageways.
This site occurs in soils on plateau uplands and contribute moisture to Ephemeral Drainageways.
This site occurs where soils have paralithic contact within 50 cm, and contribute moisture to Ephemeral Drainageways.
This site occurs where soils surfaces have strong or violent effervescence and ≥ 5% calcareous rock fragments.
This site occurs where soils are ≤ 50 cm to lithic contact with sandstone bedrock, and often supports oneseed juniper savannahs.
This site was developed for a broad range of soils that occur on upland fans, plains, hillslopes, and some depressions. The Ephemeral Drainageways site is specifically intended to target the plant communities that occur in run-on sites that are not depressions.
This site was written for a broad range of soil types that include low lying drainageways, playas and other depressions. Though close in concept, the Ephemeral Drainageway site specifically separates this type of ecology from that of a playa, which has ponding rather than flooding, accumulates more salts, and therefore has unique plant and wildlife interpretations.
Table 1. Dominant plant species
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