Natural Resources
Conservation Service
Ecological site F003XB308WA
High Cirque Walls Forest mountain hemlock
Last updated: 5/10/2024
Accessed: 12/30/2024
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
This area includes the west slope and parts of the east slope of the Cascades Mountains in Washington and Oregon. The Olympic Mountains in Washington State are also included. These mountains are part of a volcanic arc located at a convergent plate boundary. Volcanic rocks predominate but metamorphic and sedimentary rocks occur in the North Cascades and Olympic Mountains. Topography is generally dissected and steep, but some areas consist of constructional volcanic platforms and isolated stratovolcanoes. Elevation is usually 500 to 6000 feet but reaches to 14,410 ft at the summit of Mount Rainier. Many areas hosted alpine glaciers or ice sheets during the Pleistocene, and a few remain today.
Climate becomes cooler and moister with increasing elevation and latitude. Low elevations experience a long growing season and mild temperatures. High elevations can accumulate snowpack lasting into summer and frost may occur in any month. Average annual precipitation ranges from 60 to 180 inches in most areas. Most precipitation falls during the fall, winter, and spring during low-intensity frontal storms. Summers are relatively dry. Average annual temperature is 27 to 50 degrees F. The frost-free period is 10 to 180 days.
LRU notes
The Olympic Mountains land resource unit is composed of the mid to upper elevation areas on the Olympic Peninsula in northwest Washington. It occurs primarily on the eastern side of the peninsula above the warmer, lower Olympic foothills of MLRA 2.
Large amounts of rain and snow contribute to a very moist environment and a considerable stream and river network. Major rivers that have headwaters in the LRU include the Elwha, Wynoochee, and Skokomish Rivers.
Lithology is primarily oceanic sedimentary rock stacked in an accretionary wedge and coastal basalt that has been metamorphosed and vertically uplifted into a large horseshoe shape called the Crescent Formation (Washington Geological Survey). This chaotic collection of rock in many cases has been metamorphosed. These geologic materials were heavily modified by Pleistocene alpine glaciation. Contemporary glaciers which receive copious amounts of yearly snowfall continue to sculpt the dissected valleys with runoff.
Soils are primarily Spodosols, Inceptisols, and unique Andisols developed from non-volcanic materials.
The LRU has a strong rainshadow effect and areas on the northeastern side of the peninsula are considerably drier than near-Pacific western slopes. Vegetation is primarily dense forest. At lower elevations, western hemlock (Tsuga heterophylla) is the dominate tree species; western redcedar (Thuja plicata) is quite common in moist areas and Douglas-fir (Pseudotsuga menziesii ) is common in drier areas. Pacific silver fir (Abies amabilis) and mountain hemlock (Tsuga mertensiana) are the primary tree species in the higher elevations; subalpine fir (Abies lasiocarpa) and Alaska cedar (Callitropsis nootkatensis) can be widespread as well.
Classification relationships
Mountain hemlock/Alaska huckleberry, mountain hemlock/Alaska huckleberry/beargrass
Ecological site concept
This ecological site resides on cirques and mountain slopes in the mountain, at elevations of 2,800 to 4,080 feet on slopes 45 to 85 percent. The climate is cold and moist (105 to 125 frost free days, mean annual precipitation of 135 to 205 inches and average annual air temperature of 38 to 41 Fahrenheit). Site conditions are harsh with heavy, persistent, late melting snowpack that results in a short growing season. The soils are primarily Andisols with medial-skeletal textures. Andic soil properties are derived from the extreme weathering environment and higher amounts of organic matter in the soil; volcanic ash influence is minimal. Parent material is primarily colluvium derived from basalt. The soil temperature regime is cryic and the soil moisture regime is udic. Soils have lithic contacts within 40 inches of the soil surface. The reference community overstory is primarily mountain hemlock and Pacific silver fir may have high cover. The understory generally has high cover of Alaska huckleberry (Vaccinium alaskensis) with a diversity of other species including: white avalanche-lily (Erythronium montanum), strawberryleaf raspberry (Rubus pedatus), oval-leaf blueberry (Vaccinium ovalifolium), thinleaf huckleberry (Vaccinium membranaceum), deer fern (Blechnum spicant), oneleaf foamflower (Tiarella trifoliata var. unifoliate), common beargrass (Xerophyllum tenax), bride’s bonnet (Clintonia uniflora), rusty menziesia (Menziesia ferruginea), and mosses. A variety of seral tree species are present including western hemlock (Tsuga heterophylla), western redcedar (Thuja plicata) on warmer, lower elevation sites and subalpine fir (Abies lasiocarpa) and Alaska cedar (Callitropsis nootkatensis). At the highest elevations, the overstory has only mountain hemlock (Tsuga mertensiana) and the understory has pink mountainheath (Phyllodoce empetriformis), Cascade bilberry (Vaccinium deliciosum), western moss heather (Cassiope mertensiana), oval-leaf blueberry (Vaccinium ovalifolium), common beargrass (Xerophyllum tenax), thinleaf huckleberry (Vaccinium membranaceum), Sitka valerian (Valerian sitchensis). Avalanches can occur on this site. Diseases and insect damage include Annosus root rot, laminated; heart and butt rot, hemlock dwarf mistletoe, or rusty red stringy rot. Lightning strikes are common, though because of snowpack, limited fuels, fires caused by lightning tend to be small, patch disturbances. Stand replacement fires that are very rare occur with a rotational interval of 1000 years in the Olympic Mountains. Generally, mountain hemlock in the Pacific Northwest during pre-logging times had fire rotation intervals of 600 years. 0710411 North Pacific Mountain Hemlock Forest – Wet Biophysical Setting from LANDFIRE is 1000 years.
Associated sites
F003XB307WA |
High Mountain Slopes Forest Pacific silver fir |
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Similar sites
F003XA308WA |
High Cirque Forest mountain hemlock |
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F003XC309WA |
Mountain Slopes Parkland and Forest whitebark pine |
Table 1. Dominant plant species
Tree |
(1) Tsuga mertensiana |
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Shrub |
(1) Vaccinium alaskaense |
Herbaceous |
Not specified |
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