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Scientific Name: Columbia Basin Palouse Prairie
Unique Identifier: CES304.792
Classification Confidence: 2 - Moderate

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Summary: This once-extensive grassland system occurs in eastern Washington and Oregon, and west-central Idaho, though in very small patches there. In much of its range it is characterized by rolling topography composed of loess hills and plains over basalt plains. The climate of this region has warm-hot, dry summers and cool, wet winters. Annual precipitation is high, 38-76 cm (15-30 inches). The soils are typically deep, well-developed, and old. The cool-season bunchgrasses that dominate the vegetation are adapted to this winter precipitation. Characteristic species are Pseudoroegneria spicata and Festuca idahoensis with Hesperostipa comata, Achnatherum scribneri, Leymus condensatus, Leymus cinereus, Koeleria macrantha, Pascopyrum smithii, or Poa secunda. Shrubs commonly found include Amelanchier alnifolia, Rosa spp., Eriogonum spp., Symphoricarpos albus, and Crataegus douglasii. Excessive grazing, past land use and invasion by introduced annual species have resulted in a massive conversion to agriculture or shrub-steppe and annual grasslands dominated by Artemisia spp. and Bromus tectorum or Poa pratensis. Remnant grasslands are now typically associated with steep and rocky sites or small and isolated sites within an agricultural landscape.

Classification Approach: International Terrestrial Ecological Systems Classification (ITESC)

Similar Ecological Systems
Unique Identifier Name
CES304.083 Columbia Plateau Steppe and Grassland
CES304.993 Columbia Basin Foothill and Canyon Dry Grassland
CES306.040 Northern Rocky Mountain Lower Montane, Foothill and Valley Grassland

Component Associations
Association Unique ID Association Name
CEGL001130 Symphoricarpos albus - Rosa nutkana Shrubland
CEGL001448 Eriogonum sphaerocephalum / Poa secunda Dwarf-shrub Grassland
CEGL001449 Eriogonum thymoides / Poa secunda Dwarf-shrub Grassland
CEGL001479 Leymus cinereus Alkaline Wet Meadow
CEGL001509 Festuca idahoensis - Symphoricarpos albus Grassland
CEGL001615 Festuca idahoensis - Eriogonum caespitosum Grassland
CEGL001619 Festuca idahoensis - Hieracium cynoglossoides Grassland
CEGL001620 Festuca idahoensis - Koeleria macrantha Grassland
CEGL001626 Rosa nutkana - Festuca idahoensis Grassland
CEGL001662 Pseudoroegneria spicata - Balsamorhiza sagittata - Poa secunda Grassland
CEGL001670 Pseudoroegneria spicata - Festuca idahoensis Palouse Grassland
CEGL001677 Pseudoroegneria spicata - Poa secunda Grassland
CEGL001678 Pseudoroegneria spicata - Poa secunda Lithosolic Grassland
CEGL001679 Pseudoroegneria spicata - Hesperostipa comata Grassland
CEGL001704 Hesperostipa comata - Poa secunda Grassland
CEGL001746 Elymus lanceolatus - Hesperostipa comata Grassland
CEGL001782 (Balsamorhiza serrata) - Poa secunda Grassland
CEGL001784 Eriogonum compositum / Poa secunda Dwarf-shrub Grassland
CEGL001785 Eriogonum douglasii / Poa secunda Dwarf-shrub Grassland


Land Cover Class: Herbaceous
Spatial Pattern: Large patch
Natural/Seminatural: No
Vegetated ( > 10% vascular cover):
Upland: Yes
Wetland: No
Isolated Wetland: No

Diagnostic Classifiers
Primary Classifier Secondary Classifier
Loess deposit (undifferentiated)  
Deep Soil  
Mineral: W/ A-Horizon >10 cm  
Cool-season bunch grasses  
Long (>500 yrs) Persistence  

Non-diagnostic Classifiers
Primary Classifier Secondary Classifier
Lowland Foothill
Lowland Lowland
Temperate Temperate Continental

At-Risk Species Reported for this Ecological System
Scientific Name
  (Common Name)
NatureServe Global Status U.S. Endangered Species Act Status
Leymus condensatus
  (Giant Wildrye)

Vegetation Composition (incomplete)
Species Name Rounded Global Status Growth Form Stratum Char-
Domi-nant Con-stant
Cover Class %
Balsamorhiza sagittata G5 Flowering forb Herb (field)    
Eriogonum heracleoides G5 Flowering forb Herb (field)    
Phlox longifolia G5 Flowering forb Herb (field)    
Bromus briziformis GNR Graminoid Herb (field)    
Bromus tectorum GNR Graminoid Herb (field)    
Festuca idahoensis G5 Graminoid Herb (field)    
Poa pratensis G5 Graminoid Herb (field)    
Pseudoroegneria spicata G5 Graminoid Herb (field)    

Animal Species Reported for this Ecological System
Scientific Name
  (Common Name)
Global Status U.S. Endangered Species Act Status Charact-
Microtus montanus
  (Montane Vole)
Peromyscus maniculatus
  (North American Deermouse)
Reithrodontomys megalotis
  (Western Harvest Mouse)
Urocitellus columbianus
  (Columbian Ground Squirrel)

Color legend for Distribution Map
Nation: United States
United States Distribution: ID, OR, WA
Nation: Canada
Canadian Province Distribution: BCpotentially occurs
Global Range: This system occurs in eastern Washington and Oregon, and west-central Idaho.

Biogeographic Divisions
Division Code and Name Primary Occurrence Status
304-Inter-Mountain Basins C: Confident or certain
306-Rocky Mountain P: Predicted or probable

The Nature Conservancy's Conservation Ecoregions
Code Name Occurrence Status
6 Columbia Plateau Confident or certain
8 Middle Rockies - Blue Mountains Predicted or probable

MRLC 2000 Mapzones
Code Name Occurrence Status
8 Grande Coulee Basin of the Columbia Plateau Confident or certain
9 Blue Mountain Region Confident or certain
10 Northwestern Rocky Mountains Predicted or probable

National Mapping
ESLF Code (Ecological System Lifeform): 7115
ESP Code (Environmental Site Potential): 1142
EVT Code (Existing Vegetation Type): 2142

West Landfire Legend: Yes
East Landfire Legend: No

Element Description Edition Date: 14Jan2014
Element Description Author(s): M.S. Reid

Ecological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

  • Comer, P., D. Faber-Langendoen, R. Evans, S. Gawler, C. Josse, G. Kittel, S. Menard, C. Nordman, M. Pyne, M. Reid, M. Russo, K. Schulz, K. Snow, J. Teague, and R. White. 2003-present. Ecological systems of the United States: A working classification of U.S. terrestrial systems. NatureServe, Arlington, VA.

  • Daubenmire, R. 1988. Steppe vegetation of Washington. Washington State University Cooperative Extension Service Publication EB1446. (Revised from and replaces Washington Agricultural Experiment Station Publication XT0062.) 131 pp.

  • LANDFIRE [Landfire National Vegetation Dynamics Database]. 2007a. Landfire National Vegetation Dynamics Models. Landfire Project, USDA Forest Service, U.S. Department of Interior. (January - last update) [] (accessed 8 February 2007).

  • Shiflet, T. N., editor. 1994. Rangeland cover types of the United States. Society for Range Management. Denver, CO. 152 pp.

  • TNC [The Nature Conservancy]. 2013. Climate Wizard. The Nature Conservancy, University of Washington, and The University of Southern Mississippi. [] (accessed September 19, 2013).

  • Tisdale, E. W. 1982. Grasslands of western North America: The Pacific Northwest bunchgrass. Pages 223-245 in: A. C. Nicholson, A. Mclean, and T. E. Baker, editors. Grassland Ecology and Classification Symposium, Kamloops, BC.

  • WNHP [Washington Natural Heritage Program]. 2018. Unpublished data files. Washington Natural Heritage Program, Department of Natural Resources, Olympia, WA.

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Version 7.1 (2 February 2009)
Data last updated: March 2019