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Snake-Columbia shrub steppe

The Snake/Columbia Shrub Steppe is a vast, mostly arid ecoregion. Its easternmost limit is the Continental Divide in eastern Idaho. From there, the ecoregion follows the arc of the Snake River Plain as far as Hell's Canyon. The ecoregion then spreads throughout southeastern Oregon, extending along the Deschutes River basin to the Columbia River. It also includes, following hydrographic lines, parts of northern Nevada and the extreme northeast of California. To the north, the ecoregion dominates the western portion of the Columbia Basin in Washington.

The ecoregion is largely in the rain shadow of the Cascade Mountains and thus receives little precipitation. Latitude and physiography are influential factors in distinguishing this ecoregion from other similar ecoregions, such as the Wyoming Basin and Great Basin Shrub Steppes. The Snake/Columbia Shrub Steppe is lower in elevation than the Wyoming Basin, and the two are separated by mountainous areas.

  • Scientific Code
    (NA1309)
  • Ecoregion Category
    Nearctic
  • Size
    84,200 square miles
  • Status
    Critical/Endangered
  • Habitats

Description
Biological Distinctiveness
The dominant vegetation in the ecoregion is sagebrush (Artemisia spp.), typically associated with various wheatgrasses (Agropyron spp.), Idaho fescue (Festuca idahoensis) or other perennial bunchgrasses (Franklin and Dyrness 1988). The ecoregion contains a number of isolated mountain ranges in the southern parts of Idaho and Oregon, and here the sagebrush shrublands grade into bunchgrasses and juniper woodlands. Some parts of these ranges contain areas of Douglas-fir (Psuedotsuga menziesii), subalpine fir (Abies lasiocarpa), and aspen (Populus tremuloides) (Wuerthner 1986). Riparian zones in the ecoregion typically contain cottonwoods (Populus spp.) and willows (Salix spp.) (West 1988). The ecoregion exhibits more desert-like vegetation in southeastern Oregon, where elevation is considerably higher and precipitation lower (Franklin and Dyrness 1988). The same area, however, contains extensive wetlands, which provide vital waterfowl habitat in the Pacific Flyway.

The Great Basin is hotter and drier than the Snake/Columbia, lacks distinct major watersheds, and exhibits vegetation associations indicative of its proximity to true desert ecoregions like the Mojave. The ecoregion lacks the floristic diversity found in the Great Basin ecoregion. Situated as it is in a distinct major river system with consistent climatic and physiographic features, the Snake/Columbia ecoregion forms a logical single unit.

Fire, grazing, and variations in precipitation and temperature are the major disturbances in the ecoregion. Burning may encourage grass growth and impede sagebrush. Sagebrush, on the other hand, adapts to drought conditions that kill grasses (West 1988).

The Owyhee drainage (SW Idaho and SE Oregon) once supported salmon runs, making it one of the few high desert anadromous spawning areas.

Conservation Status

Habitat Loss and Degradation
Overgrazing by domestic livestock, fire suppression and resultant high-intensity blazes, and spread of exotic grasses are the major anthropogenic changes to the ecoregion. Loss of perennial grasses is a major problem in this ecoregion. Irrigation in the Washington and Idaho portions of the ecoregion have also caused major changes and have encouraged the spread of exotic species. Wuerthner (1988) notes the loss of bluebunch wheatgrass (Agropyron spicatum) communities in the Owyhee Uplands portion of the ecoregion due to overgrazing in arid conditions.

Remaining Blocks of Intact Habitat
Large intact areas, though degraded by overgrazing and exotic grass invasion, remain in southwestern Idaho, southeastern Oregon, and northwestern Nevada. Defense installations, such as the Yakima Firing Range and the Hanford Nuclear Reservation, also protect extensive habitat areas in Washington.

Degree of Fragmentation
Conversion of native habitat to agriculture, particularly in eastern Idaho and in Washington, are major sources of fragmentation. Exotic grass and noxious weed invasions are likewise becoming serious enough to cause fragmentation.

Degree of Protection
Defense installations, National Wildlife Refuges, National Monuments, and Wilderness Study Areas provide a fair degree of protection. However, without control of exotic grass and noxious weed invasions, protected areas may have a limited benefit in the long run. Important protected areas include:

•Yakima Firing Range - southern central Washington
•Hanford Reservation - southern central Washington
•Hart Mountain National Antelope Refuge - southern Oregon
•Malheur National Wildlife Refuge - southeastern central Oregon
•Craters of the Moon National Monument - southern Idaho
•Birch Creek Fen Preserve (TNC)
•Sheldon National Wildlife Refuge - northwestern Nevada
Types and Severity of Threats
Livestock grazing, invasion of exotic plants, irrigated agriculture, and recreation, especially through use of offroad vehicles, are the major threats to the ecological integrity of this ecoregion. As there are no highly effective methods for checking or reversing the tide of exotic and noxious plant invasions, the spread of these species and consequent elimination of native plant communities is a serious threat. Combined with overgrazing and continued conversion to row crops, the ecoregion may be seriously altered and degraded in the near future.

Suite of Priority Activities to Enhance Biodiversity Conservation

•Timely designation of wilderness study areas as actual wilderness areas is a high priority.
•As defense installations are phased out, it will be important to maintain these sites as protected areas.
•Targeting specific sites and vegetation communities for protection from severe overgrazing will also be vital.
•Developing effective techniques for combating invasive species is a high priority as well.
•Restoration of salmon fisheries is an interesting prospect that could have major implications for certain systems within the ecoregion.
•Major reductions in livestock grazing on public lands are urgently needed.
Conservation Partners

•Idaho Conservation League
•Oregon Wildlife Federation
•Oregon Natural Desert Association
•Oregon Natural Resources Council
Relationship to other classification schemes
The ecoregion boundary follows Omernik (1995). It encompasses Bailey's units 342 B, C, D, H, and I. It corresponds to Küchler's 49, 44, 45, 39, and some of 34 for the same geographic area.

Prepared by: S. Primm.

 

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