Cascade Mountains leeward forests

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This ecoregion stretches as a narrow band along a north-south axis along the leeward side of the Cascade Mountains that straddle the Canada-U.S. border in the province of British Columbia and Washington state.

In the southern half of the ecoregion the mean annual temperature is 6°C, mean summer temperature is 15°C, and mean winter temperature is -3.5°C. In the northern half of the ecoregion, temperatures are approximately 2.5°C cooler. A strong climatic gradient exists from the moist coastal climate to the semiarid continental climate of the southern interior. Precipitation ranges from 300 mm in the south to 500 mm in the north, and also ranges from 600 mm in the east to 1200 mm in the west (ESWG 1995).

The southern half of the ecoregion is made up of the Cascade Ranges, a mountainous upland within the southern Pacific Ranges. The Chilcotin Ranges make up the northern half of the ecoregion, and reach elevations of up to 2700 m asl. The Okanagan Range in the south runs along the Canada-United States border (ESWG 1995).

  • Scientific Code
  • Ecoregion Category
  • Size
    17,900 square miles
  • Status
    Relatively Stable/Intact
  • Habitats

Biological Distinctiveness
Alpine tundra communities consist of Engelmann spruce (Picea engelmanii), subalpine fir (Abies lasciocarpa), and lodgepole pine (Pinus contorta). Montane forests are made up of lodgepole pine, quaking aspen (Populus tremuloides), white spruce (P. glauca), and Douglas fir (Pseudotsuga menziesii) with a pine grass understory. At the lowest elevations in the eastern region there is a parkland of scattered ponderosa pine (P. ponderosa) in a matrix of bluebunch wheatgrass (Agropyron spp.) and sagebrush (Atremesia tridentata) grasslands (ESWG 1995).

This ecoregion is home to bighorn sheep (Ovis canadensis), mountain goat (Oreamnos americanus), grizzly and black bear (Ursus arctos and U. americanus), black-tailed deer (Odocoileus hemionus), coyote (Canis latrans), blue grouse (Dendragapus obscurus), cougar (Puma concolor), and various raptors in the southern part of the region (ESWG 1995). Large numbers of salmon (Oncorhynchus spp.) use the Fraser River as a major migration corridor. The ecoregion contains habitat for the endangered spotted owl (Strix occidentalis).

Conservation Status

Habitat Loss
Nearly 70 percent of the ecoregion is considered to remain as intact habitat. A variety of human activities occur in the ecoregion, including logging, base metal mining, small areas of agriculture in the lower elevations, cattle grazing in lower elevation areas and some sheep grazing in alpine areas and some significant transportation corridors.

Remaining Blocks of Intact Habitat
There are few large blocks of remaining habitat left in this ecoregion. Some remaining blocks include:

•South Chilcotin-Spruce Lake
•Stein Valley
•Manning Park
•Snowy Mountain
•Degree of Fragmentation
The Fraser River is a natural movement barrier to the north/south movement of small mammals, ungulates and carnivores. However, the construction of several major east-west highways and railways, complete with high fencing in some cases, has further disrupted the north-south movement of species such as grizzly and black bears, wolverine, and fisher.

Degree of Protection

•Ts’yl-os Provincial Park - British Columbia - 2332.4 km2
•North Cascades National Park - north-central Washington
•Big Creek-South Chilcotin Provincial Park - British Columbia - 868 km2
•Manning Provincial Park - British Columbia - 658.84 km2
•Cathedral Provincial Park - British Columbia - 332.72 km2
•Lower Stein Wilderness Area - British Columbia - 330 km2
•Skagit Valley Recreation Park - British Columbia - 325.08 km2
•Marble Range Provincial Park - British Columbia - 180 km2
•Cascade Recreation Park - British Columbia - 166.8 km2
•Edge Hills Provincial Park - British Columbia - 130 km2
•Upper Stein Wilderness Area - British Columbia - 100 km2
Types and Severity of Threats
Outside of protected areas, there are significant threats to forests on both the U.S. and Canadian sides of the border. There are additional threats from mineral exploration, and rural/recreational developments adjacent to some of the lakes in the ecoregion (e.g. Carpenter Lake).

Suite of Priority Activities to Enhance Biodiversity Conservation

•New protected areas established at Spruce Lake and Snowy Mountain in British Columbia.
•Restoration of suitable corridors to enable dispersal of mammalian species in a north-south direction.
Conservation Partners

•Canadian Parks and Wilderness Society, British Columbia Chapter
•The Nature Conservancy, British Columbia
•Nature Trust of BC
•Northwest Wildlife Preservation Society
•Sierra Club, Western Canada
•World Wildlife Fund Canada
Relationship to other classification schemes
The Chilcotin Ranges (TEC 204) make up the northern part of the Cascade Mountains Leeward Forests, the Interior Transition Ranges (TEC 208) lie in the southern part, and the small Okanagan Range area (TEC 210) in the far south is included as well (Ecological Stratification Working Group 1995). Ponderosa Pine and Douglas-fir Montane forest (2), Interior and Coastal Subalpine forest (2-3), Grassland and Tundra all characterize this south-central area of British Columbia (Rowe 1972).

Prepared by: K. Kavanagh, M. Sims