Pacific Northwest Coast

Description & Physiography

The Pacific Northwest Coast ecoregion includes most of the Olympic Peninsula of Washington, the coast mountain ranges extending down to central Oregon, and most of Vancouver Island in British Columbia. Approximately 11 percent of Washington is within this ecoregion. As of 1991, about 5 percent of the Washington portion had been converted to agricultural or urban uses.

The Olympic Mountains, the ocean coast and coastal plain, and the Willapa Hills are the ecoregion’s dominant landforms in Washington. Glaciated peaks in the Olympic Mountains rise to an elevation of nearly 8,000 feet above sea level. Streams and rivers typically begin as deeply incised, steep gradient drainages that eventually feed large, low-gradient river systems on the coastal plain. The coastal plain is up to 20 miles wide on the Olympic Peninsula and mostly underlain by glacial till and outwash. Major estuaries and associated dunes are found on the southern coast. The Willapa Hills are well-rounded highlands with old, well-weathered soils.

Climate

High precipitation typifies the ecoregion, averaging 60 to 240 inches annually. Most precipitation falls as rain from November through April. Snow pack and rain-on-snow zones cover a considerable area only in the Olympic Mountains. As a result of a rain shadow effect, the northeastern Olympic Mountains receive the lowest precipitation of equivalent elevations anywhere in western Washington. Along the outer coast and adjacent valleys, fog and cool temperatures in the summer are important climatic factors.

Plants & Animals

Coniferous forests dominate the vegetation of the ecoregion. Lowland forests are dominated by western hemlock, Douglas-fir, and western redcedar. In the coastal fog belt, Douglas-fir is rare and Sitka spruce becomes abundant. Forests in the mountains are mostly dominated by Pacific silver fir and mountain or western hemlock. High elevations in the Olympic Mountains have subalpine parkland and alpine habitats.

Two of the largest estuaries on North America’s west coast are part of this ecoregion. Other special habitats include coastal dunes, wetlands, riparian areas, and sphagnum bogs. The Olympic Mountains are rich in rare plant species due to their isolation, the number of unusual habitats, and the presence of steep environmental gradients. They include species endemic to the Olympic Mountains as well as species that are disjunct from other mountainous areas.

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Links to Completed Ecoregional Assessments

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