![](/images/logos/USDA-logo.png)
Natural Resources
Conservation Service
Ecological site AX003X00D004
Western Middle Cascades Frigid Udic Forest Group
Last updated: 5/09/2024
Accessed: 08/17/2024
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
The Cascade and Olympic Mountains (MLRA 3) include 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 Western Cascades land resource unit (LRU E) is located in western Oregon. It is bounded by the Santiam River on the north, the High Cascade volcanic platform on the east, the Rogue-Umpqua Divide on the south, and the Willamette and Umpqua Valleys on the west. This area is equivalent to the area generally known as the “Old Cascades.”
Bedrock consists of basalt and andesite of the Sardine Formation overlying the Little Butte Volcanic Series which contains soft tuff (Orr, et al. 1992). The Sardine Formation “cap” is absent at many locations. Topography is dissected and steep in most areas. Areas of low relief contain ancient and contemporary landslides. Alpine glaciation occurred in headwater basins during the Pleistocene but subsequent mass movement has partially obscured glacial features (Noller, et al. 2016).
Soil moisture regime is udic or aquic. Soil temperature regime ranges from mesic to cryic. Soils in this LRU generally have higher apparent clay content compared with those to the north and Spodosols do not occur. Most soils contain an appreciable amount of volcanic glass. Inceptisols usually have isotic mineralogy. Andisols are usually amorphic and meet the second criteria for andic soil properties (Soil Survey Staff, 2014). Ultisols can occur at the lowest elevations.
Conifer forest is the dominant vegetation. Natural fire is dominantly moderately frequent, mixed-severity (Spies, et al. 2018). Franklin and Spies (1991) noted an increase in tree bole fire scars south of 44.5 degrees latitude in the Oregon Cascades. This LRU hosts small amounts of fire-tolerant species common in the Siskiyou-Trinity Area (MLRA 5) but absent in areas to the north. These species include Pacific madrone (Arbutus menziesii), incense cedar (Calocedrus decurrens), giant chinkapin (Chrysolepis chrysophylla), and sugar pine (Pinus lambertiana).
At low to mid elevations, Douglas-fir (Pseudotsuga menziesii) is a long-lived, early-seral tree; western hemlock (Tsuga heterophylla) is an associated shade-tolerant tree. Red alder (Alnus rubra) is a short-lived, early-seral tree. It occurs ephemerally on uplands but persists on wet or repeatedly-disturbed sites.
At high elevations, Noble fir (Abies procera) is an early-seral tree; Pacific silver fir (Abies amabilis) is an associated shade-tolerant tree. Sitka alder (Alnus viridis ssp. sinuata) and vine maple (Acer circinatum) form persistent shrubfields on sites subject to heavy snowpack or avalanches. Wetlands typically support shrubby or herbaceous vegetation.
Classification relationships
This ecological site group description covers a variety of cool western hemlock plant associations including the following (McCain and Diaz 2002):
• Western hemlock / twinflower
• Western hemlock / devilsclub / Oregon oxalis
• Western hemlock / devilsclub / starry false lily of the valley
• Western hemlock / Pacific rhododendron / salal
• Western hemlock / Pacific rhododendron / twinflower
• Western hemlock / Pacific rhododendron / Cascade barberry
• Western hemlock / Pacific rhododendron / Oregon oxalis
• Western hemlock / Pacific rhododendron / common beargrass
• Western hemlock / Alaska blueberry / bunchberry dogwood ,
• Western hemlock / Alaska blueberry / Oregon oxalis
• Western hemlock / Alaska blueberry - devilsclub
Ecological site concept
This forested site occurs in the cooler portion of the western hemlock zone. Soil temperature regime is frigid, and soil moisture regime is udic. Forest litter turnover and associated nutrient cycling can be slow compared with warmer sites, but rapid compared with colder sites. Elevation is typically 2000 to 4000 feet.
Associated sites
AX003X00B003 |
Western Middle Cascades Mesic Udic Forest Group Lower elevations, drier and warmer sites. |
---|---|
AX003X03F007 |
Glaciated Middle Cascades Cryic Udic Forest Group Higher elevations, cooler and wetter sites. |
Similar sites
AX003X03C004 |
Glaciated Middle Cascades Frigid Udic Forest Group Similar position, but on the Glaciated portion of the Western Cascades. |
---|
Table 1. Dominant plant species
Tree |
(1) Pseudotsuga menziesii |
---|---|
Shrub |
(1) Rhododendron macrophyllum |
Herbaceous |
Not specified |
Legacy ID
F003XE004OR
Click on box and path labels to scroll to the respective text.