Flora of the Lower Watershed

Habitat and plant species diversity in the Cedar River Municipal Watershed is significant. The Watershed spans elevations from 538 feet at Landsburg to 5,447 feet at Meadow Mountain at the Cascade Crest. Precipitation ranges from 57 inches to more than 140 inches at higher elevations. Plant habitats here are correspondingly diverse and include bogs and forested fens, extensive riparian forests, ancient coniferous forests, subalpine and arctic-alpine meadows and lakes, and scree/talus.

About 95 percent of the lower Watershed is dominated by a relatively homogeneous canopy of second-growth coniferous or mixed coniferous/deciduous forest that regenerated after the original timber harvest (between 1880 and 1920). Only about 734 acres of unharvested native forest remain in the lower Watershed. Old growth that does persist exists in relatively small, isolated stands surrounded and widely separated by continuous stands of young and mature second-growth forest. About 12,255 acres of the lower Watershed has second-growth forests between 70 and 119 years old. Though older stands and second-growth stands differ dramatically in structural characteristics and biological diversity, these forests are generally dominated by Douglas-fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), and western redcedar (Thuja plicata), with a minor presence of grand and noble firs (Abies grandis and A. procera).

Western hemlock dominates the mid-understory of most stands and is also the most commonly found and most prolific tree species naturally regenerating under existing canopies in second-growth forest stands. Shrub layers are usually dominated by vine maple (Acer circinatum), salal (Gaultheria shallon), and sword fern (Polystichum munitum) where canopies are relatively closed, and include salmonberry (Rubus spectabilis) and other Rubus species where canopies are more open. Mixed stands containing both coniferous and deciduous species such as big leaf maple (Acer macrophyllum) are also present in many areas of the lower Watershed, but are found mostly in forested wetland and riparian habitats, along with Sitka spruce (Picea sitchensis). Pure hardwood stands dominated by red alder (Alnus rubra) are infrequent and located mostly in especially wet or riparian areas.

There are also non-native species that have established in disturbed areas of the Watershed, especially along roads and major structures like the Masonry Dam and the Bonneville Power Administration's 500 kV power transmission line through the lower Watershed. Common invasive species include Tansy Ragwort (Senecio jacobaea), Japanese Knotweed (Polygonum cuspidatum), and Scot Broom (Cytisus scoparius). Non-native garden ornamentals persist in areas that were once small towns or homesteads. These include English Holly (Ilex aquifolium), English Ivy (Hedera helix), Monkey-puzzle Tree (Araucaria araucana), and Lilac (Syringa vulgaris).

Until recently, the full depth of the plant life of the Watershed has been largely unexplored. But, with the help of the Friends and its many volunteers, Watershed staff are currently documenting this rich botanical heritage. The scientific collection of dried plant specimens being created is stored at the University of Washington Herbarium. In addition, as part of its Watershed Stewardship Program, the Friends is working with the City of Seattle to remove invasive plants from the Watershed. Learn more about the Watershed Stewardship Program and volunteering your time.