The North Cascades ecoregion

Ecoregions provide a useful framework and background for the discussion of marine, freshwater, and terrestrial environs of the county. The discussion of ecoregions is based on U.S. Environmental Protection Agency (EPA) ecoregion conventions, which result in units similar to European biogeographical regions because they denote areas of general similarity in ecosystems.

King County map, showing incorporated land and major water bodies. Copyright King County.
King County map, showing incorporated land and major water bodies. Copyright King County.

EPA’s ecoregions have been mapped across the North American continent and are classified hierarchically into four levels of increasing complexity and detail. There are only 15 Level I ecoregions across the entire continent, and King County falls within 2 of these: Marine West Coast Forests and Northwestern Forested Mountains. There are 52 Level II ecoregions, and the two that occur across King County correspond identically with the Level I ecoregions: Marine West Coast Forest and Western Cordillera. Level III regions describe smaller ecological areas nested within level II regions. There are three Level III ecoregions in King County: Puget Lowlands, Cascades, and North Cascades. Level IV ecoregions describe an even finer scale of nested ecological areas and allow locally defining characteristics to be identified and more specific management strategies to be formulated for such local conditions. In King County, there are nine Level IV Ecoregions (see Table 2 and Landscape Diversity Map).

Table 2. Level III and Level IV Ecoregions that lie within King County’s geographic boundaries..

Level III

Level IV

Puget Lowland


Eastern Puget Riverine Lowlands

Eastern Puget Uplands

Central Puget Lowland

North Cascades

North Cascades Lowland Forests

North Cascades Highland Forests

North Cascades Subalpine/Alpine



Western Cascades Lowlands and Valleys

Western Cascades Montane Highlands

Cascade Subalpine/Alpine


The North Cascades Ecoregion

From the Puget Ecoregion, we move upslope into the North Cascades Ecoregion and its three component Level IV ecoregions: North Cascade Lowland Forests, North Cascade Highland Forests, and the North Cascades Subalpine/Alpine. Together, these ecoregions comprise approximately 1,838 square kilometers (656 square miles) and extend from about 244 meters (800 feet) ASL in the river bottoms to over 2,134 meters (7,000 feet) at the Cascade crest.

North Cascade Lowland Forests

The North Cascade Lowland Forests are the lowest (in elevation) extension of the Cascade Ecoregion and encompass the upslope valleys of King County’s major river systems: the Skykomish River Valley in the northeast, the Tolt River Valley in the north, and the three forks of the Snoqualmie (North, Middle, and South) in eastern King County. Of these, the Skykomish forests penetrate farthest to the east, approaching within a few miles of the Cascade Crest. These are deeply cut valleys for the most part, and it is possible to traverse from the river bottom to subalpine heights on a single slope. In doing so, one would walk from lush forests of the river bottom through several plant communities in a relatively short horizontal distance. In the river bottoms, the lowland forests of western hemlock, western redcedar, and Douglas-fir were historically dominant—large trees with dense canopies that kept the river bottoms cool and moist. These forests were the focus of much logging in the late 19th and early 20th centuries and had been mostly logged off by the end of WWI.  As logging operations ceased in these valleys, the lands were left to regenerate. These forests grow quickly in the valley bottoms but the new stands are little like the old and complex forests that once stood here. Still, the new forests are gaining in age and structure as they are left to re-grow or are newly managed for ecological benefits as well as commodity value.

It is in this ecoregion that the relationship among forests, rivers, and Pacific Salmon reaches a zenith. The often closed canopy of the bottomland forests maintains a tunnel of cool air above the river, and the canopy helps keep waters cool; leaf and needle-fall are building materials for aquatic insects (some of which are dependent on the needles of particular species of conifer for their cases; one particular species of caddisfly has declined, for example, because the needles of Sitka Spruce are now in short supply). Aquatic insects are important food for young salmon. Trees that fall in rivers via windthrow and riverbank erosion provide cover, create complex habitats, and trap the gravels necessary for salmon spawning. In fact, in these rivers, this large woody debris (as it has come to be called) is a critical component of healthy salmon habitat. Much of the wood that finds its way to lower rivers and on into our coastal estuaries originates in this ecoregion and is delivered by floods to the lower reaches. The three forks of the Snoqualmie, however, lie above Snoqualmie Falls which is an impassable barrier to up-migrating Pacific salmon. These rivers still play an important role in moving nutrients, wood, and gravel into the lower mainstem river where salmon reside. Despite the history of logging, this ecoregion remains largely forested with regenerated stands and is slowly regaining basic ecological functions important to riparian and aquatic biodiversity.

North Cascade Highland Forests

The North Cascades Highland Forest Ecoregion lies between 854 meters (2,800 feet) ASL and approximately 1700 meters (5,600 feet) and covers approximately 874 square kilometers (312 square miles); ownership is dominated by the US Forest Service (the Mt. Baker-Snoqualmie National Forest), although there is considerable private land at the lower elevations of this ecoregion. This ecoregion is the heart of the Pacific Silver Fir (PSF) zone, and the namesake species may occur in almost monotypical stands at mid-elevations. In the upper reaches of this zone, Pacific Silver Fir often blends with Alaskan cedar, mountain hemlock, and even subalpine fir. This terrain is often the steepest and, coupled with deep snowfall, makes for severe snowpack instability on some western slopes. These areas are known as avalanche tracks and are easily seen as long, vertical strips of shrubs and other non-tree vegetation. The consistent and violent disturbance of avalanches has produced a distinct vegetation community that contrasts with the adjacent forests. In the place of large conifers, dense thickets of shrub-like mountain alder, vine maple, and mountain maple, with flexible and bowed stems, dominate many of the tracks. But not all tracks have proven to be the same; the composition of the vegetation communities, though all shrubby and flexible to avalanche surges, tends to be related to the frequency of the avalanche disturbance: the greater the frequency of disturbance, the fewer conifers and the more mountain alder and other low shrubs. This pattern makes for considerable diversity amid the forest stands and the tracks are feeding grounds for a variety of subalpine and highland animals.

This ecoregion was one of the last remaining timber-producing areas within King County until the late 1970s. Finally, in 1989, the last mill capable of cutting old-growth size logs was closed.  With the growth of population in the lowlands to the west, the forest has lately become a major recreational destination. Forest production from this area is now mainly confined to private lands although some harvest occurs on state and federal lands. What remains of the forest outside the wilderness and roadless areas is mainly a forest with little structural diversity mostly of the same species and age in stands less than 50 to 75 years old.

North Cascades Subalpine/Alpine

The North Cascade Subalpine and Alpine Ecoregion extends from about 854 meters (2,800 feet) ASL to almost 2,400 meters (7,900 feet) ASL at Mt. Daniel, the highest point in King County. The dramatic landscapes of the North Cascade subalpine/alpine ecoregion of King County cover 452 square kilometres (161 square miles) and are the work of continental and alpine glaciers. This area comprises the least disturbed landscapes in the County. However, human influence and effect is present here too: old mining claims, most now abandoned or unworked, dot the alpine landscape, and the area is used heavily for recreation by the citizens of King County and Puget Sound. Most of the subalpine and alpine landscape is contained within two wilderness areas: the Alpine Lakes Wilderness in east central King County and the Henry M. Jackson Wilderness in the far northeast corner of the county. The Alpine Lakes Wilderness is a landscape of small mountain lakes nestled among the high rock peaks and timbered valleys of the region. Approximately 500 of these small lakes are found in King County. Over half of Washington State's population lives within a one-hour drive of the Wilderness. With nearly 150,000 visitors each year, the wilderness areas have suffered considerable damage in all accessible areas.

Snow Lake. Photo by Jennifer Vanderhoof.

The Subalpine Ecoregion is dominated by mountain hemlock, which extends from the Pacific Silver Fir-dominated zone to timberline, occasionally intermixed with Alaskan Cedar and scattered Pacific Silver Fir, and often set amid open subalpine meadows or “alpine parkland.” Heavy snowpack at this elevation often persists into mid to late-summer and suppresses the growth of trees except in a few scattered locations. These meadows come to be dominated by a mix of heathers (not true Old World heathers but related), mountain huckleberry, and sedges at higher elevations. These meadows often bear the brunt of heavy use by hikers. The steady use of informal trails through heather meadows degrades and eventually destroys plant cover. The ribbon of trail cuts deeper into the soil and is further aided by erosive forces of wind and snowmelt until the track is shin-deep. When the trails reach that point, they are often abandoned for a parallel track and the process begins again. Restoration of these meadows has become a constant activity of the Forest Service in recent years and many areas have been closed to foot traffic until the area is healed, a process that takes many years.

An alert visitor to these meadows and parklands will see a variety of animals, some residents of the subalpine and others that travel from lower elevations to graze or hunt during the spring and summer. Among the more charismatic animals are elk, black-tail deer, black bear, and cougar; rarely seen, except by their tracks or other sign, are grey wolves and Grizzly bears, two species that are making a return to the Cascades after being eradicated earlier in the century (see Mammals discussion below). Two avian species, both faithful indicators of this ecoregion, are Clark’s nutcracker and the gray jay. Ruffed grouse are common but rarely seen in the brushy areas, and goshawk and golden eagles hunt over the meadows.  Year-round residents of this ecoregion are rare because of the harsh winters, but one in particular typifies the close fit between habitat and inhabitant: the marmot is the most recognizable animal that is regularly encountered in this region. Both the hoary and the yellow-bellied marmot can be found throughout the North Cascades.

The summit of the Cascade rim is only a few hundred feet above these meadows and parklands, and the boundary between subalpine and true alpine, the timberline, is often characterized by the presence of dwarfed conifers or krummholz, much as in the Alps and other mountain ranges of the world. Heather meadows can be expected in the wetter areas of these stony slopes, along with patches of black sedge, mountain heliotrope, and Alaskan spirea. On the uppermost alpine ridges, the terrain is stony (called fellfields in other parts of the world), plant cover is sparse, and only a few species find footholds in this extreme habitat: sandworts, fleabanes, wild buckwheat, and saxifrages are the most conspicuous plants. Little has changed in this landscape since the large alpine glaciers departed from these ridges and slopes.

About the Author: 
Robert Fuerstenberg, Jennifer Vanderhoof, Jonathan Frodge, Kathryn Gellenbeck, Kollin Higgins, Klaus Richter, and Kim Stark collaborated to write the King County Biodiversity Report, which was published by the King County Department of Natural Resources and Parks as part of the Local Action for Biodiversity (LAB) project, a global biodiversity initiative. The report serves as the foundation of a plan for long-term protection of biodiversity in King County. Citation: King County. 2007. King County biodiversity report. King County Water and Land Resources Division, Department of Natural Resources and Parks. Prepared for International Council for Local Environmental Initiatives (ICLEI), Biodiversity Initiative. 102 pp.