King County riparian habitat

Riparian habitats are often characterized by particular trees and shrub species that line the banks of most rivers and streams in the lowlands and foothills of King County.

A section of Griffin Creek. Photo copyright King County.
A section of Griffin Creek. Photo copyright King County.

These habitats tend to be used by a diversity of species out of proportion to the area represented by streamsides. Although riparian habitats occupy only about 2 percent of the landscape, they contain more species than the surrounding uplands. Over 50 percent of the wildlife species of Western Washington (birds, mammals, and herptiles) use riparian zones regularly. Some species like the Pacific giant salamander might be considered wholly dependent on riparian habitats because they breed in streamside forests and feed in the rivers and lakes bounded and protected by riparian habitats.

In addition, riparian habitats provide critical functions to the aquatic habitats they bound: litter and insects for food, shade to moderate temperatures, large wood for instream habitat structure, and nutrient transformation that influences water quality. In most cases, small streams were bounded directly by the forest stands through which they flowed; any true riparian habitats tended to lie along the very stream edge and be very narrow. Typical plants of this zone along small streams include salmonberry, Pacific ninebark, several willow species, and red alder. Alongside larger streams and rivers in King County, the riparian habitats were historically among the most complex habitats in the landscape. The dynamics of flow in Puget Sound rivers—floods and droughts—controlled the location, species recruitment and survival, and community composition of the riparian habitats. In a transect from river to upland, one could historically traverse willow breaks, newly sprouted cottonwoods, mature cottonwood, Oregon ash, and Sitka spruce, each species closely associated with the flood regime of the river. Along the river, the communities became more complex as various patches responded to the dynamics of the river and to the work of beaver in the sloughs and side channels. Given this complex array of habitats, ages, and communities, it is no surprise that riparian habitats are often considered keystones of richness and diversity.

Few examples of pre-settlement riparian habitats remain in the lowlands and foothills of King County. Most of the riparian habitats that now line our river and streams have been greatly simplified. The American beaver, an aptly named “ecosystem engineer,” is now relatively rare compared to pre-settlement times, and their handiwork can no longer be found as easily (they are making a comeback in some places, however, and ecologists celebrate each evidence of a new beaver dam in the side channels of our rivers). Furthermore, the flow regimes of our large rivers have been largely regulated to reduce flooding and the damage to homes and businesses; the damage to the riparian ecosystem has increased, however, as the disturbances mainly responsible for the variety of plant communities have been eliminated. Our riparian habitats today are dominated by red alder, and occasional cottonwood stands, some older than the dams that now regulate the river. The fate of future stands often rests with volunteers and agencies that sponsor riparian planting events to reinvigorate the habitats that were once invigorated by floods.

Despite the changes these lowland and foothill landscapes have undergone, the diversity of habitats supports a tremendous diversity of wildlife species. The high species richness is a function of the broad distribution of habitat types and the diversity of habitat types across the large area. However, these habitats are also prone to invasion by exotic species, both plants and animals, and are also the source of many non-native species that have invaded nearby native habitats. Often the species that occupy these habitats are either habitat generalists or species that are using the disturbed habitats for feeding while nesting in less disturbed habitats nearby. Others are seasonal migrants using the habitats as resting stopovers or winter feeding areas.

In the highlands and sub-alpine areas, riparian habitats are generally much reduced as headwater streams are quite small and often flow steeply through narrow canyons and gorges. These streams are often bordered by vegetation characteristic of the adjacent terrestrial habitats.  In some low gradient areas, more extensive riparian habitats develop where beaver have dammed streams forming ponds or where small lakes interrupt the stream. The resulting pond and wetland systems provide complex habitats that support many species of birds, mammals, and amphibians. Distinctive plant types and communities may form in these wet areas and include saxifrage (Saxifraga sp.), willow-herb (Epilobium sp.), monkey flowers (Mimulus sp.), rein orchid (Habenaria sp.), and bluebells (Mertensia sp.). Where peaty soils form, sedges of the genus Carex, low shrubs of Labrador tea (Ledum) and bog laurel (Kalmia), and a few distinctive herbs such as marsh marigold (Caltha leptosepala). arnica (Arnica sp.), and pedicularis (Pedicularis sp.) can be found.


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.