City of Seattle, Seattle Public Utilities, Riparian Permanent Sample Plots 2003-current, Cedar River Municipal Watershed, King County, WA

The City of Seattle’s Cedar River Municipal Watershed is managed to support and supply clean drinking water to the greater Seattle area. The watershed covers 91,000 acres, hosts a rich diversity of plants, animals, and habitats, and is owned by the City of Seattle. From 2003 to 2005, Seattle Public Utilities established 61 permanent sample plots (PSP) in riparian habitats of the Cedar River Municipal Watershed. 31 of these plots (plot #s 1-31) were established in 2003 upstream of Chester Morse Lake, the drinking water reservoir for the City of Seattle. 30 additional plots (plot #s 32-61) were established in 2005 downstream of Chester Morse Lake. In 2012, 6 of the 61 total plots (plot #s 4, 11, 12, 27, 28, 29) were resampled and the sampling methods were simplified. Each sampling year had different surveyors.

The riparian permanent sample plots were limited to low gradient, moderately to unconfined reaches along the Cedar River and its tributaries because they typically show the most variability in riparian condition, stream-riparian interactions are greatest, and fish use is highest. Sites were randomly selected along these reaches, with two plots located at each site, one on each side of the stream. Sites were stratified into four stand types: deciduous dominated, mixed deciduous/conifer, conifer dominated in stem exclusion phase with little understory, and conifer dominated differentiated with well-developed understory, with at least five plots in each type.

Each plot was measured for tree species and diameter, snag diameter and height, shrub species and cover, herb species and cover, sapling species and cover, percent canopy cover, and other species found in the plots but not previously recorded in the tree, shrub, and herb sampling.

Selection of riparian plots for resampling in 2012 was designed to include plots in second and old growth forests and with medium and large stream sizes. Future resampling is expected to occur at an approximately ten-year interval. The third resampling effort is expected to begin in 2025. This data package will be updated after resampling efforts occur.