King County lowland habitat

Red alder, a deciduous species that often grows in disturbed areas. Photo copyright King County.
Red alder, a deciduous species that often grows in disturbed areas. Photo copyright King County.

The history of land use in King County has produced a lowland and foothill landscape of bewildering variety. The once continuous forest of western hemlock, Douglas-fir, and redcedar has given way to a patchwork of lawns, parks, playgrounds, woodlots, greenbelts, old fields, croplands, tree farms, and remnant forests set amid a landscape of urban, suburban, rural, and commercial uses, all joined and, at the same time, separated by a vast network of roads and communication corridors. Despite this apparent richness and variety of patches, this landscape is clearly human-dominated, and habitats for native species have generally been marginalized by the scale and pace of land conversion and resource extraction. This pattern is not, of course, unusual in the history of development. Even so, over the last 30 years, King County has made significant strides in protecting and preserving a variety of habitat types that are critical components of biodiversity. We will discuss the following terrestrial habitat types: forests and woodlands; greenbelts, parks, and corridors; meadows, old fields, hedgerows, and shelterbelts; and riparian habitats.  

Forests and woodlots

The large forest blocks within King County lie mainly in the foothills where logging is still the dominant land use; some of these lands are in private hands, some in state ownership, and some in County ownership. Virtually all these lands have been harvested at least once, and the forests tend to be dominated by early to mid-successional stands of conifers, under 70 years old—many under 50. The few exceptions lie in small blocks of a few hundred acres at most and include two small stands (each less that 11 hectares, 25 acres) of old growth forest in the City of Seattle, Federation State Forest, a 215-hectare (490-acre) grove of old growth in the White River valley of southeastern King County, 3-4 remnant stands in the Green River Valley, and a stand in the Mt. Si Natural Resource Conservation Area (see Landscape Diversity map). Most estimates put the total extent of virgin (uncut) old-growth lowland forest in King County at less than about 10 percent of the historic amount. Except for some “pioneer stands”, none of this forest occurs at elevations below 305 meters (1,000 feet). The best known examples of this historic forest are indicated by the tree symbols on the biodiversity map.

A small patch of remaining old growth in West Seattle. Photo by Robert Fuerstenberg.

Forest management has taken a decidedly ecological turn in the last two decades and local public forest lands have begun to show the effects of this enlightened technique. Tiger Mountain State Forest in central King County and City of Seattle’s Municipal Cedar River Watershed  have worked diligently with local forest ecologists to shape their management toward recovering old growth structure in their forests. The results have been encouraging: the forest are showing multiple layers of vegetation, a lush ground cover of mosses and ferns, greater diversity in age classes, and greater species diversity faster than expected. King County is attempting the same sort of management on its working forest lands and awaits the results in 20 to 30 years.

These forests are exceptions to the general rule, however, and the most stands still harvested for commercial purposes are patch and block cuts where regaining ecologically sound forest structure is not an objective. These forests tend to be composed of many even-aged blocks with very high stem densities that are periodically thinned over the life of the stand. The harvest cycle may be as short as 35 years or as long as 70 in some cases; these forests tend to be almost monotypical where one or two species dominate the forest, and the forest floor may be almost devoid of a groundstory.  Forest edges are sharp and abrupt, patch size is small, and deep forest microclimates are largely absent. Animal diversity in these forests, especially avian diversity, is much lower than in the ecologically managed stands discussed above.   

Adjacent to the agricultural areas of the county, forests tend to be a mix of conifer and deciduous trees, remnants of more extensive stands that have been left to regenerate on their own. Most of these stands are small woodlot patches of a few 10s of acres (at most) that border fields or surround wetlands, or have regrown after fields were abandoned. Red alder, a pioneer species in cutover lands, and Douglas-fir dominate these forest patches, and the understory may be almost entirely composed of Himalayan blackberry, a non-native member of the genus Rubus that was brought to the Pacific Northwest with the first settlers. On the wetter lands of the valley bottoms, small stands of black cottonwood dot the floodplains amid the fields. Many of these stands are regrowth that followed the first wave of clearing, but a few stands in the Snoqualmie valley are probably the progeny of the original trees and have attained girths approaching 1.2 meters (4 feet). These stands and other scattered along our major rivers provide important resting stations for neotropical migrant birds on their way to the northern boreal forests to breed.

Closer to the urban fringe, many forest blocks lie within or surround residential subdivisions and are the remains of former tree farms converted to urban uses. Some of these forest stands are required to remain intact by County development codes and are termed “open space” tracts. These woodlands are kept in protective status in perpetuity, presumably managed by the associations that are established by the residents of the subdivision. More often, these early successional, mixed stands are neglected and are overtaken by invasive species, many of which escape from the landscaping of the development. In addition, most open space forests associated with subdivisions are relatively small, isolated from adjacent tracts by roads, and penetrated by both formal and informal trails that allow recreational use by local residents (but not by the wider public).

Greenbelts, parks, and corridors

Despite the scale of development in the urban and suburban areas, visitors to King County invariably remark on the number of trees that occur in the developed areas of the county. Once again, many of the remaining stands are in greenbelts, urban separators, riparian buffers, and open space parks. These areas have been set aside by city and County codes or occur on steep slopes, or were enshrined in parks earlier in the century. Nevertheless, these habitats are common and regular features of the urban/suburban landscape. Some of these vegetated features are remnants of stands planted by the farmers who were lately resident here and reflect species preferred by them or by conservation agents seeking to protect soil and water. Other stands are the remains of orchards or woodlots; still others were planted by the first urban dwellers some 30 years ago and are large and old enough that their origins are lost on the new residents. Some greenbelts and corridors protect steep slopes on hillsides or in ravines and have a wild look about them—these open spaces still retain many of the native species that once dominated the area, but they are also home to escapes such as English ivy and holly. Whatever their origins, those who live near these green spaces are highly protective of them, and many citizens have taken it upon themselves to laboriously remove the non-native invaders from these spaces.

There are a few notable parks in this area that appear to be centers of high species diversity amid the urban landscape, at least for birds and small mammals. Cougar Mountain Regional Wildland Park, a King County-owned area, lies at the very edge of the urban area and is a kind of outpost of the Western Cascade Lowland Ecoregion. Almost 1,360 hectares (3,100 acres) in size, it is by far the largest park in the County system and comprises conifer stands, deciduous ravines and riparian areas, and mixed forest habitats. It is the first in a series of foothills that align from west to east into the Cascade Highlands. Next in line to the east is Squak Mountain State Natural Area, further east is West Tiger Mountain Natural Resource Conservation Area, and finally the Rattlesnake Mountain Scenic Area. This extensive corridor seems to provide a pathway for avian species to and from the highlands and gives Cougar Mountain a higher than expected richness of birds. This unanticipated richness suggests that Cougar Mountain may be a kind of biodiversity “hotspot” in the lowland landscape of King County.  

Meadows, old fields, hedgerows, and shelterbelts

Set amid the farmlands of King County that still occupy the Snoqualmie valley, the middle Green Valley, the White River valley, and the Enumclaw Plateau are many habitats that are artifacts of the agricultural use of this land, both past and present. Some resemble habitats long altered—the meadows and old fields of the Enumclaw area in south King County are a facsimile of the unusual prairie habitats that dotted this upland in 1850. Others are the remains of land management activities from a bygone era—the aging shelterbelts and windbreaks of blue spruce, eastern juniper, Lombardy poplar, and white pine that still line a few farmsteads or stand along lanes. Some—hedgerows—are accidents of marking fields with rough-cut posts that sprouted branches or are neglected fencerows of Nootka rose and elderberry. Many of these anthropogenic habitats have probably become substitutes for the native types that have been lost.

Agriculture is common in King County river valleys. Photo copyright King County.

In the river valleys, along the wet bottomlands, rowcrops gave way to pastureland for dairies that has, in turn, given way to abandoned fields. Some of these fields have reverted to shallow ponds and swampy meadows, with clumps of willow and red-osier dogwood on the margins. These habitats are stopovers for waterfowl and also harbor amphibians, prey for frequently seen Great Blue Herons. These wetlands are also the haunts of water shrews and meadow voles, and the Northern Harriers that hunt them. But they are also the habitats of many exotic species: nutria, Virginia opossum, and American bullfrogs, to name a few. Other, somewhat drier fields have become meadows dotted with shrubby pioneers such as elderberry and black hawthorn, or invading Scot’s broom. These habitats provide food and cover for ground-nesting birds, including Savannah Sparrows.

Along the drier upland meadows and abandoned fields, Red-tailed Hawks can be seen perched on fence posts, telephone poles, and trees hunting for the abundant mice and voles that make these oldfields home. These abandoned fields are often overgrown with non-native thistles, and American Goldfinches can be seen flitting from patch to patch.

Shelterbelts, also called windbreaks, can attract a diversity of birds, especially if they are the only trees for some distance. In the open lands of the Enumclaw plateau, for example, windbreaks and the occasional woodlot account for considerable bird diversity and are important nesting sites in the agricultural landscape. 

Hedgerows and fencerows, though small, provide food, shelter, and habitat to many species that use these “edge” habitats and give some measure of structural diversity to otherwise monotonous fields and pastures. Other habitats of these areas include field borders, roadsides (if they are left unsprayed), and the occasional abandoned stock pond.

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.