Natural Resources
Conservation Service
Ecological site F003XN941WA
Southern Washington Cascades Wet Frigid Coniferous Forest
Last updated: 5/10/2024
Accessed: 11/14/2024
General information
Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.
MLRA notes
Major Land Resource Area (MLRA): 003X–Olympic and Cascade Mountains
Steep mountains and narrow to broad, gently sloping valleys characterize this MLRA. A triple junction of two oceanic plates and one continental plate is directly offshore from Puget Sound. Subduction of the oceanic plates under the westerly and northwesterly moving continental plate contributes to volcanic activity in the Cascade Mountains. Movement among these plates has resulted in major earthquakes and the formation of large stratovolcanoes. The Cascade Mountains consist primarily of volcanic crystalline rock and some associated metasedimentary rock. The mean annual precipitation is dominantly 60 to 100 inches, but it is 30 to 60 inches on the east side of the Cascade Mountains.
The soil orders in this MLRA are dominantly Andisols, Spodosols, and Inceptisols and minor areas of Entisols and Histosols. The soils are dominantly in the frigid or cryic temperature regime and the udic moisture regime. The soils generally are shallow to very deep, well drained, ashy to medial, and loamy or sandy. They are on mountain slopes and ridges.
Ecological site concept
This ecological site is in depressions and swales and on terraces, glacial-valley walls, and debris aprons in Mount Rainier National Park. Climate is a key component in the succession of the forest dynamics. The site is in cool, wet areas at middle to high elevations (1,600 to 4,600 feet).
The soils that support this ecological site are in the frigid soil temperature regime and the aquic soil moisture regime. They are poorly drained and very deep. The soils have a seasonal high water table at the surface to a depth of 10 inches below the surface at some time during the growing season. They are subject to frequent periods of ponding in April, May, and June, which has a direct effect on the vegetative productivity of the site. A thin organic horizon consisting of decomposing twigs, needles, and litter is on the soil surface. This horizon helps to protect the soils from wind and water erosion.
Western redcedar (Thuja plicata) and red alder (Alnus rubra) are the most common overstory species, but some western hemlock (Tsuga heterophylla), Douglas-fir (Pseudotsuga menziesii), and grand fir (Abies grandis) are present. The root penetration of western redcedar makes it well adapted to forested swamps. American skunkcabbage (Lysichiton americanus), Oregon oxalis (Oxalis oregana), western swordfern (Polystichum munitum), deer fern (Blechnum spicant), western oakfern (Gymnocarpium dryopteris), and twinflower (Linnaea borealis) are in scattered areas.
Associated sites
F003XN945WA |
Southern Washington Cascades Wet Low Cryic Coniferous Forest The vegetation in ecological site F003XN945WA has commonalities to that of site F003XN941WA; however, site F003XN945WA receives more precipitation and is commonly located at higher elevations. |
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Similar sites
F003XN942WA |
Southern Washington Cascades Moist Frigid Coniferous Forest Ecological site F003XN941WA, Southern Washington Cascades Wet Frigid Coniferous Forest, is similar to site F003XN942WA, Southern Washington Cascades Moist Frigid Coniferous Forest. Ecological site F003XN941WA is wetter and will frequently pond water on the soil surface between April and June. Site F003XN942WA has a high seasonal water table starting at a depth of 10-20 inches from the soil surface at some point during the growing season. |
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F003XN943WA |
Southern Washington Cascades Frigid Coniferous Forest Ecological site F003XN941WA, Southern Washington Cascades Wet Frigid Coniferous Forest, is similar to site F003XN943WA, Southern Washington Cascades Frigid Coniferous Forest. F003XN943WA has a lower water table and higher water-holding capacity. The vegetation ranges from the more wet-adapted species, such as western redcedar and American skunkcabbage, in site F003XN941WA to drier species, such as western hemlock and Cascade Oregon grape, in site F003XN943WA. |
Table 1. Dominant plant species
Tree |
(1) Thuja plicata |
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Shrub |
Not specified |
Herbaceous |
(1) Lysichiton americanus |
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