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Riparian Ecosystem Management Study Area

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Location of study regions relative to major features of Washington state. 

Data are being collected from two sub-regions of the Pacific Coast Range in southwest Washington.  Both sub-regions fall within the Western Hemlock Zone, with the eastern sub-region transitional to the Puget Trough physiographic province (Franklin and Dyrness, 1973).

Sub-region 1 (Capitol Forest, Thurston County) is a 37,000 ha parcel of public land centered approximately 5 km southwest of Puget Sound's southern tip.  Dominant coniferous species are:

  • Douglas fir (Pseudotsuga menziesii (Mirbel) Franco).
  • Western hemlock (Tsuga heterophylla (Raf.) Sarg.)
  • Western red cedar (Thuja plicata Donn ex D. Don). 

Sub-region 2 (Willapa Hills) is centered near Menlo, Wa, approximately 10 km inland from the Pacific Ocean coast, Pacific County.  Dominant coniferous species are:

  • Western hemlock (T heterophylla)
  • Sitka spruce (Picea sitchensis (Bong.) Carr.)
  • Western red cedar (T. plicata.) 

Both sub-regions are dominated by moderate-to-steep slopes zoned primarily for timber production, from which primary forest (so called old growth) was harvested 60-80 years previous to our study. Forest structure is primarily coniferous, with hardwoods (mostly red alder, Alnus rubra Bong.) invading riparian areas. Elevation ranges from near sea level to 764 m. Sub-region 1 geology is primarily basaltic; sub-region 2 is mixed basalts and marine sediments. Study site soils were predominantly silt loam, with pockets of gravelly and cobbly loam in sub-region 1. Climate is winter wet, summer dry, with little rainfall May-September. The sub-regions are similar in mean annual temperature but sub-region 2 receives nearly twice the rainfall as sub-region 1.


Franklin, S.F. and C.T. Dyrness. 1973. Natural Vegetation of Oregon and Washington. U.S. Dept. of Agriculture Forest Service, PNW-GTR-8, 471 pp.