Palouse Prairie

EVT 7142Columbia Basin Palouse Prairie

CES304.792GNRHerbGrassland

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.

Source: NatureServe Explorer

Vegetation

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.

Source: NatureServe Explorer

Environment

Source: NatureServe Explorer

Dynamics

Fire is the primary disturbance factor. Fires were low intensity due to limited fuel and significant internal spacing between fuel patches. Currently, Bromus tectorum and other introduced grasses often invade these habitats after fire, building up a dense fuelbed that creates frequent, high-intensity fires that are lethal to native perennial grasses (Landfire 2007a). The historic frequency was 50 years to maintain this grassland (Landfire 2007a). Extending fires frequency to >50 years leads to increased shrub cover and shrub regeneration (Landfire 2007a).

Source: NatureServe Explorer

Threats

A massive conversion to agriculture resulting in a scattering of remnant grasslands is now typically associated with steep and rocky sites or small and isolated sites within an agricultural landscape. Conversion of this type has commonly come from agriculture (wheat farming) historically and is nearly complete except for remnants on sites too steep or rocky to farm (Landfire 2007a). Conversion of remnants is the result of altered fire regimes with fire suppression (fire frequency >50 years) that has allowed succession (Landfire 2007a) and conversion to deciduous shrublands and/or invasion and domination of non-native species. Common stressors and threats include fragmentation from agriculture and roads, altered fire regime from fire suppression and indirectly from livestock grazing and fragmentation, and introduction of invasive non-native species (Landfire 2007a). Potential climate change effects could include a loss of remnant patches of this ecosystem, if climate change has the predicted effect of less effective moisture with increasing mean temperature (TNC 2013).

Source: NatureServe Explorer

Distribution

This system occurs in eastern Washington and Oregon, and west-central Idaho.

Source: NatureServe Explorer

Ecologically Associated Plant Species

Plant species that characterize this ecosystem type, organized by vegetation stratum. These are species ecologically associated with the ecosystem, not confirmed present in any specific area.

Shrub/sapling (tall & short)

Amelanchier alnifolia, Crataegus douglasii, Symphoricarpos albus

Herb (field)

Achnatherum scribneri, Balsamorhiza sagittata, Bromus briziformis, Bromus tectorum, Eriogonum heracleoides, Festuca idahoensis, Hesperostipa comata, Koeleria macrantha, Leymus cinereus, Leymus condensatus, Pascopyrum smithii, Phlox longifolia, Poa pratensis, Poa secunda, Pseudoroegneria spicata

Source: NatureServe Ecological System assessment

Ecologically Associated Animals (4)

Animal species ecologically associated with this ecosystem type based on NatureServe assessment. These are species whose habitat requirements overlap with this ecosystem, not confirmed present in any specific roadless area.

Mammals (4)

Common Name	Scientific Name	G-Rank
Montane Vole	Microtus montanus	G5
North American Deermouse	Peromyscus maniculatus	G5
Western Harvest Mouse	Reithrodontomys megalotis	G5
Columbian Ground Squirrel	Urocitellus columbianus	G5

Source: NatureServe Ecological System assessment

At-Risk Species Associated with this Ecosystem (1)

Species with conservation concern that are ecologically associated with this ecosystem type. G-Rank indicates global conservation status: G1 (critically imperiled) through G5 (secure). ESA status indicates U.S. Endangered Species Act listing.

Common Name	Scientific Name	G-Rank	ESA Status
Giant Wildrye	Leymus condensatus	G3G4	--

Source: NatureServe Ecological System assessment

Component Associations (18)

Plant community associations that occur within this ecological system. Associations are the finest level of the U.S. National Vegetation Classification (USNVC) and describe specific, repeating assemblages of plant species. Each association represents a distinct community type that may be found where this ecosystem occurs.

Name	G-Rank
(Balsamorhiza serrata) - Poa secunda Grassland	G2	NatureServe
Elymus lanceolatus - Hesperostipa comata Grassland	G1	NatureServe
Eriogonum compositum / Poa secunda Dwarf-shrub Grassland	G2	NatureServe
Eriogonum douglasii / Poa secunda Dwarf-shrub Grassland	G2	NatureServe
Eriogonum sphaerocephalum / Poa secunda Dwarf-shrub Grassland	G3	NatureServe
Eriogonum thymoides / Poa secunda Dwarf-shrub Grassland	G3	NatureServe
Festuca idahoensis - Eriogonum caespitosum Grassland	G2	NatureServe
Festuca idahoensis - Hieracium cynoglossoides Grassland	G1	NatureServe
Festuca idahoensis - Koeleria macrantha Grassland	G3	NatureServe
Festuca idahoensis - Symphoricarpos albus Grassland	G1	NatureServe
Hesperostipa comata - Poa secunda Grassland	G1	NatureServe
Pseudoroegneria spicata - Balsamorhiza sagittata - Poa secunda Grassland	G2	NatureServe
Pseudoroegneria spicata - Festuca idahoensis Palouse Grassland	G1	NatureServe
Pseudoroegneria spicata - Hesperostipa comata Grassland	G4	NatureServe
Pseudoroegneria spicata - Poa secunda Grassland	G4	NatureServe
Pseudoroegneria spicata - Poa secunda Lithosolic Grassland	G3	NatureServe
Rosa nutkana - Festuca idahoensis Grassland	G1	NatureServe
Symphoricarpos albus - Rosa nutkana Shrubland	G3	NatureServe

State Conservation Ranks (3)

Subnational conservation status ranks (S-ranks) assigned by Natural Heritage Programs in each state where this ecosystem occurs. S1 indicates critically imperiled at the state level, S2 imperiled, S3 vulnerable, S4 apparently secure, and S5 secure. An ecosystem may be globally secure but imperiled in specific states at the edge of its range.

State	S-Rank
ID	SNR
OR	SNR
WA	SNR

Methodology and Data Sources

Ecosystem classification: Ecosystems are classified using the LANDFIRE 2024 Existing Vegetation Type (EVT) layer, mapped to NatureServe Terrestrial Ecological Systems via a curated crosswalk. Each EVT is linked to the USNVC (U.S. National Vegetation Classification) hierarchy through pixel-level co-occurrence analysis of LANDFIRE EVT and NatureServe IVC Group rasters across all roadless areas.

Vegetation coverage: Coverage percentages and hectares are derived from zonal statistics of the LANDFIRE 2024 EVT raster intersected with roadless area boundaries.

Ecosystem narratives and community species: Sourced from the NatureServe Explorer API, representing professional ecological assessments of vegetation composition, environmental setting, dynamics, threats, and characteristic species assemblages.

IVC hierarchy: The International Vegetation Classification hierarchy is sourced from the USNVC v3.0 Catalog, providing the full classification from Biome through Association levels.

Component associations: Plant community associations listed as components of each NatureServe Ecological System. Association data from the NatureServe Explorer API.

State ranks: Conservation status ranks assigned by NatureServe member programs in each state where the ecosystem occurs.