Ministry of Environment Ecology

PART II
Ecoregion Unit Descriptions

Dry Ecodomain

This Ecodomain covers the southern interior plateau and is an extension of the dry climate regime that occupies the interior of northern Mexico and the northwestern United States. Its two most commonly recognized climates are arid desert and semiarid steppe. In British Columbia this Ecodomain is represented by only one Ecodivision.

Semi-Arid Steppe Highland Ecodivision

Southern Interior Ecoprovince

This Ecodivision occurs within the Dry Ecodomain in southern British Columbia and includes the leeward ranges of the Coast Mountains, the Thompson Plateau, the Clear Range, the Okanagan Range, and the western side of the Okanagan and Shuswap highlands. Winters are cold and the summers are warm to hot. Vegetation in the valleys and basins is typically steppe or bunchgrass prairie that may contain sagebrush or occasional ponderosa pine or Douglas-fir. At higher altitudes, subalpine coniferous forests can become established. In British Columbia this Ecodivision is represented by only one Ecoprovince.

Southern Interior Ecoprovince

Location - This Ecoprovince lies east of the crest of the Coast and Cascade ranges and west of the Columbia Mountains. It is the southernmost part of the Interior Plateau system. This Ecoprovince includes the Thompson Plateau, the Pavilion Ranges, the eastern portion of the Cascade Ranges, and the western margin of the Shuswap and Okanagan Highlands.

Climate - The leeward portion of the coastal mountains and the drier portion of the highlands are included because they share much the same climate as the main plateau. Because the Ecoprovince lies in the rain shadow of the Coast and Cascade Mountains it contains some of the warmest and driest areas of the province in summer. Air moving into the area has already lost most of its moisture on the west facing slopes of the coastal mountains. There are occasional irruptions of hot">dry air from the Great Basin, to the south, in the summer. They bring clear skies and very warm temperatures. In winter and early spring there are frequent outbreaks of cold, dense Arctic air because there is no effective barrier in the north. However, such events are less frequent than on the plateaus further north.

Biogeoclimatic Zonation - Vegetation is dominated by three zones, the Bunchgrass Zone in the lower slopes of the large basins, the Interior Douglas-fir Zone on the lower elevations of the plateau surface, and the Montane Spruce Zone on the higher elevations of the plateaus. The Engelmann Spruce - Subalpine Fir Zone occurs on the higher elevation of the plateaus and highlands, the Alpine Tundra Zone occurs on the highest slopes of the Okanagan and Clear ranges, the Ponderosa Pine Zone occurs sporadically on middle slopes of the large, dry basins, and the Interior Cedar - Hemlock zone occurs on the upper slopes in the northeastern area of this Ecoprovince.

Fauna - Mule deer are the most abundant large ungulate in this Ecoprovince, although the white-tailed deer has been extending its range westward from the Okanagan Basin and the Okanagan and Shuswap highlands. Bighorn sheep, both native California bighorn and the introduced Rocky Mountain bighorn, occur on the rugged grasslands throughout the Thompson and Okanagan valleys and in the Clear Ranges.

Characteristic small mammals include spotted bats, pallid bats, Nuttall's cottontails, white-tailed jack rabbits, Great Basin pocket mice, and western harvest mice.

This Ecoprovince has the greatest diversity of birds in the interior of British Columbia and the most breeding species of all the Ecoprovinces; it holds 74% of all bird species known to occur and 70% of those species known to breed in the province. It is the centre of breeding abundance in the province for Swainson's Hawk, California Quail, Mourning Dove, Burrowing Owl, Long-eared Owl, White-throated Swift, Lewis' Woodpecker, Williamson's Sapsucker, Pygmy Nuthatch, Western Kingbird, yellow-breasted Chat, and Lark Sparrow. Some species breed nowhere else in British Columbia; Ferruginous Hawk, Prairie Falcon, Gray Partridge (introduced), Chukar (introduced), California Gull, Flammulated Owl, Common Poorwill, Black-chinned Hummingbird, and White-headed Woodpecker; others breed nowhere else in Canada: Canyon Wren, Sage Thrasher, and Gray Flycatcher. It contains the only site in Canada that supports a major population of Tundra Swans during the winter.

The racer and western rattlesnake are characteristic reptiles. Tiger salamanders and Great Basin spadefoot toads are found nowhere else in the province.">The racer and western rattlesnake are characteristic reptiles. Tiger salamanders and Great Basin spadefoot toads are found nowhere else in the province.

This Ecoprovince supports both anadromous and freshwater fish. Anadromous species include, Pacific lamprey, steelhead, chinook salmon, sockeye salmon, and white sturgeon. Freshwater fish include, rainbow trout (both native and widely transplanted populations), brook trout (introduced), Dolly Varden, mountain whitefish, lake chub, redside shiner and northern squawfish.

Ecoprovince Subdivisions - The Southern Interior Ecoprovince is divided into four Ecoregions containing twelve Ecosections.

• The Okanogan Highland Ecoregion is a transitional mountain area lying between the Columbia Basin to the south and the Columbia Mountains to the northeast. This Ecoregion contains two Ecosections.

• The Southern Okanogan Basin Ecosection is a wide trench located between the Okanagan Ranges Ecoregion to the west and the Southern Okanagan Highlands to the east. This Ecosection has some of the hottest and driest climates in British Columbia.
• The Southern Okanogan Highland Ecosection is a hot, dry transitional mountain area of low rounded ridges and narrow valleys.

 

• The Northern Cascade Ranges Ecoregion lies in the strong rainshadow created by the western Cascade Mountains and is very dry. It is the northern extent of an Ecoregion that extends along the east slope of the Cascade Range from the Columbia River. This Ecoregion is represented by two Ecosections in British Columbia.

• The Hozameen Range Ecosection lies on the east side of the Cascade Ranges' divide. It is mountainous and increases with ruggedness from north to south.
• The Okanagan Range Ecosection is characterized by high mountains with deep, dry valleys that on the eastern side have Bunchgrass and Ponderosa Pine Zones.

 

• The Thompson - Okanagan Plateau Ecoregion is a broad plateau with low elevation basins. It has the driest and warmest climates in the province and contains 5 Ecosections. The Thompson - Okanagan Plateau Ecoregion is a broad plateau with low elevation basins. It has the driest and warmest climates in British Columbia and contains five Ecosections.

• The Northern Okanagan Basin Ecosection is a wide trench located between the Thompson Plateau to the west and the Northern Okanagan Highlands to the east. Large lakes dominate the valley bottom, and Bunchgrass Zone is predominant on the lower valley slopes.
• The Northern Okanagan Highland Ecosection is a cool, moist, transitional mountain area, dominated by a rolling upland.
• The Northern Thompson Upland Ecosection is an area with dissected uplands. The climate is transitional between the drier and warmer climates farther south and moister and cooler climates to the north. It has warm, dry summers and mild winters with relatively high snowfall.
• The Southern Thomson Upland Ecosection is an area with flat plateau uplands, steep sided plateau walls, and two large lowlands. It has the driest climate of any plateau upland in this Ecoregion and it has two large grassland areas.
• The Thompson Basin Ecosection is a warm and exceptionally dry, low elevation area with a high diversity and abundance of wildlife.

 

• The Interior Transition Ranges Ecoregion lies on the east side of the Coast Mountains, but it has coast/interior transition climates. This Ecoregion has three Ecosections.
  

• The Leeward Pacific Ranges Ecosection has bold mountains with deep, narrow valleys in the north. While in the south the mountains become subdued.
• The Pavilion Ranges Ecosection is a mountainous upland area that is transitional with the Coast Ranges to the west and the plateau surface to the east. The Fraser and Thompson rivers have dissected the upland surface. The Bunchgrass and Ponderosa Pine Zones predominate the lower mountain slopes upland surface.
• The Southern Chilcotin Ranges Ecosection has high rounded mountains, with deep narrow valleys. Dry forests in the Alpine Tundra Zone are extensive.

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