Ecological site group description

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.

Physiography

Physiographic Features
This ecological site occurs mainly on forested backslopes of mountains and hills, and summits and treads of outwash terraces. Parent materials are till derived from mixed origins, outwash, and residuum and colluvium derived from igneous (granitic) and metamorphic rock thinly mantled by volcanic ash and loess.

Landscapes: Mountains, Valleys

Landforms: Mountain slope, Hill slope, Outwash Terraces, Stream Terraces

Elevation:
Total range = 590 to 1245 m
(1,935 to 4,085 feet)
Central tendency = 810 to 985 m
(2,655 to 3,230 feet)

Slope (percent):
Total range = 0 to 55 percent
Central tendency = 15 to 30 percent

Water Table Depth:
>200 cm
(>80 inches)

Flooding:

Frequency: None
Duration: None

Ponding:

Frequency: None
Duration: None

Aspect: 110-190-265 (central tendency)

Climate

Climatic Features

During the spring and summer, a circulation of air around a high-pressure center brings a prevailing westerly and northwesterly flow of comparatively dry, cool and stable air into the region. As the air moves inland, it becomes warmer and drier which results in a dry season beginning in the late spring and reaching a peak in mid-summer. In the fall and winter, a circulation of air around two pressure centers over the ocean brings a prevailing southwesterly and westerly flow of air into the Pacific Northwest. This air from over the ocean is moist and near the temperature of the water. Condensation occurs as the air moves inland over the cooler land and rises along the windward slopes of the mountains or highlands. This results in a wet season beginning in October, reaching a peak in winter, then gradually decreasing in the spring.

The elevation within the LRU varies from approximately 1,445 feet in the lower river valleys to over 7,600 feet in the higher terrain. The annual precipitation increases from 21 inches in the valleys to over 60 inches over the higher mountains. Winter season snowfall varies from 30 to 50 inches. Both rainfall and snowfall increase in the higher elevations. Snow can be expected after the first of November and to remain on the ground from the first of December until March or April.

In January, the average maximum temperature is near 31° F and the minimum temperature is 18° F. Minimum temperatures from -10° to -20°F are recorded almost every winter and temperatures ranging to -30° F have been recorded. In July, the average maximum temperature is 85° to 90° and the minimum temperature 45° to 50° F. Maximum temperatures reach 100° F on a few afternoons each summer and temperatures between 105° to 110° F have been recorded. Temperatures in the mountains decrease three to five degrees Fahrenheit with each 1,000 feet increase in elevation. The average date of the last freezing temperatures can be expected by mid-May and before mid-October in the warmer areas.
(Compiled from WRCC: Climate of Washington and available station data)


Frost-free period (days):
Total range = 85 to 135 days
Central tendency = 100 to 120 days

Mean annual precipitation (cm):
Total range = 510 to 1315 mm
(20 to 52 inches)
Central tendency = 710 to 950 mm
(28 to 37 inches)
MAAT (C)
Total range = 2.8 to 9.1
(37 to 48 F)
Central tendency = 5.2 to 6.8
(41 to 44 F)

Climate stations: none

Soil features

Representative Soil Features

This ecological site is associated with several soil components. The soil components can be grouped into six soil suborders. These are the Alfic Udivitrands, Andic Dystrudepts, Andic Haploxerepts, Typic Udivitrands, TypicVitrixerands, and Vitrandic Dystrudepts. These soils have developed in various thicknesses of Mazama tephra deposits (often highly mixed with loess) over several other parent materials. These parent materials are dominantly: glacial till, outwash and material weathered from sedimentary or metasedimentary rocks. The tephra layers are important for forest productivity. Where present in sufficient thickness they can: retain large amounts of water compared to other parent materials, increase cation exchange capacity and have high availability of organically bound plant nutrients.

Parent Materials:
Kind: Tephra (volcanic ash)
Origin: mixed
Kind: Till, Outwash
Origin: mixed
Kind: residuum and colluvium
Origin: Metasedimentary, other sedimentary rock

Surface Texture: (<2mm fraction)
(1) Ashy Silt Loam
(2) Ashy Sandy Loam
(3) Ashy Loam

Surface Fragments

Vegetation dynamics

Ecological Dynamics of the Site

This grand fir site is on the moister end of the grand fir series and can have many tree species occurring depending on disturbance and seed source. Douglas-fir is the main seral species and will occur in mature stands with grand fir with fire exclusion. Engelmann spruce can also be present in fire excluded mature stands. With stand replacing or mixed severity disturbance Douglas-fir, western larch, ponderosa pine, western white pine, and lodgepole pine can occur in mixed stands. Quaking aspen, paper birch, and black cottonwood can be present in early to mid-seral stands.

The bulk of this ecological site occurs in N. Idaho. In NE Washington it occurs in the Huckleberry Mountains and northeast corner of the Selkirk Mountains LRU. This site in WA tends to be on the drier side than the sites in N. Idaho. Western white pine would be more represented in N. Idaho. Western larch and ponderosa pine taking the place of white pine in WA.

Key understory species include Douglas maple, ninebark, oceanspray, serviceberry, snowberry, twinflower, honeysuckle, Oregon grape, rose, thimbleberry, pachistima, Scouler willow, spirea, pinegrass, brides bonnet, pathfinder, sweetroot, starry solomonplume, western princes pine, and white hawkweed.

Root rot and beetle kill will occur in the mature grand fir – Douglas fir stands. Western white pine once would have been more prevalent in the seral to mature stands, however, blister rust has made it a minor component of current stands. Low intensity frequent fires will favor more open western larch, Douglas-fir, and ponderosa pine stands. Mixed severity fires will create a mosaic of mixed stands of all tree species. Severe fires may create ceanothus brush fields with tree regeneration slow to reclaim the site.

Major Land Resource Area

MLRA 043A
Northern Rocky Mountains

Subclasses

• F043AY529WA–Warm-Frigid, Dry-Udic, Loamy Foothills/Mountainsides, ashy surface (Grand Fir Moist Herb) Abies grandis/Clintonia uniflora
• F043AY530WA–Warm-Frigid, Dry-Udic, Sandy Outwash Terraces, mixed ash surface (Grand Fir Moist Herb) Abies grandis/Clintonia uniflora

Stage

Provisional