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This ecoregion occupies the southern interior of British Columbia and adjacent Washington state between the Rocky Mountains to the east and the coastal ranges to the west. Mean annual temperature is around 7°C, mean summer temperature ranges from 15°C to 16.5°C, and mean winter temperature is around -2.5°C. A strong elevational gradient in precipitation occurs, ranging from 250 mm to over 1000 mm per year. On average, precipitation is in the range of 400 mm on the plateaus. This ecoregion is characterized by very warm to hot, dry summers and moderately cool winters with little snowfall (ESWG 1995). This ecoregion is composed of flat-lying Tertiary sediments and volcanic rocks 1220-1525 m asl in elevation. Its gently rolling surface is incised by many rivers below the general surface (ESWG 1995).
Vegetative cover is quite diverse in this region. It encompasses alpine, forests, and grasslands. Forest cover ranges from lodgepole pine (Pinus contorta) with quaking aspen (Populus tremuloides), white spruce (Picea glauca), and Douglas-fir (Pseudotsuga menziesii) on the plateau to Douglas-fir and pine grass at moderate mid-slope elevations. In subalpine areas, Engelmann spruce (P. engelmannii), subalpine fir (Abies lasiocarpa), and lodgepole pine grow. Valley bottoms contain ponderosa pine (P. ponderosa) with bluebunch wheatgrass (Agropyron spp.), blue grass, June-grass (Koelaria spp.) and sagebrush (Artemisia tridentata) (ESWF 1995). Characteristic wildlife of this ecoregion includes black bear (Ursus americanus), Northern river otter (Lontra canadensis), bighorn sheep (Ovis canadensis), black and white-tailed deer (Odocoileus hemionus and O. virginianus), coyote (Canis latrans), bobcat (Lynx rufus), cougar (Puma concolor), American badger (Taxidea taxus), California quail (Callipepla californica), waterfowl, blue grouse (Dendragapus obscurus) and long-billed curlew (Numenius americanus) (ESWG 1995). This ecoregion contains the northern continental range extensions of many species of reptiles, amphibians, insects and plants. Habitat Loss It is estimated that only about 20 percent of this ecoregion remains as intact habitat. Some parts of the ecoregion have been heavily altered due to growing urban expansion and conversion of land into agricultural production. This is particularly true of the valleys and basins. Upper elevations have been impacted by livestock grazing, logging, open pit mines, agriculture, and transmission and pipeline corridors. Some grasslands have been seriously over-grazed by livestock. Remaining Blocks of Intact Habitat There are few remaining unprotected blocks of habitat remaining in this ecoregion. Degree of Fragmentation Connectivity of grassland habitats for reptiles and amphibians is highly impaired in the major valleys. The connectivity of forest species is intermediate in most forest habitats, except for the major travel corridors across the Thompson Plateau where there are median dividers and 2-3 meter-high fences for great lengths. Degree of Protection
Types and Severity of Threats Many of the valley bottoms, including bunchgrass and bunchgrass/sagebrush, are under intensive pressure from agriculture and urban development. Most of the remaining patches are slated for conversion. Upland forest habitats have either been logged in the past or are all slated for logging in the future. Many of these areas lie on public lands and will remain under forest cover, although forest communities may be significantly altered or degraded.
 Relationship to other classification schemes The Thompson-Okanagan Plateau (TEC 209) comprises most of the area of the Okanagan Dry Forests, and the Okanagan Highland (TEC 211) in the south is also included in the Canadian portion of the ecoregion (Ecological Stratification Working Group 1995). In terms of forest regions, this ecoregion incorporates the Strait of Georgia Coast forest (1), Grassland, Interior Subalpine (2) and Montane forests of Ponderosa Pine and Douglas-fir (1) and Central Douglas-fir (2) (Rowe 1972). Prepared by: D. Demarchi, K. Kavanagh, M. Sims, G. Mann. This text was originally published in the book Terrestrial ecoregions of North America: a conservation assessment from Island Press. This assessment offers an in-depth analysis of the biodiversity and conservation status of North America's ecoregions. All text by World Wildlife Fund © 2001 For more general information on this ecoregion, go to the WildWorld version of this description.
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