Physiographic features

Physiographic Features

This ecological site group occurs mainly on low to mid elevation slopes of glaciated mountains and foothills. It is found predominantly on side slopes, foot slopes and terraces. The parent material is volcanic ash or mixed volcanic ash and loess over till, loamy outwash or residuum and colluvium from mainly metamorphic or granitic rock.


Landscapes: Mountains, Foothills

Landform: Mountain slope, Hill slope, Outwash Terraces, Moraines, Drainageways



Elevation:
Total range = 700 to 2095 m
(2,295 to 6,870 feet)
Central tendency = 1220 to 1570 m
(4,000 to 5,150 feet)

Slope (percent):
Total range = 0 to 80 percent
Central tendency = 20 to 45 percent

Water Table Depth:
30 to >200cm
(12 to >80 inches)


Flooding:

Frequency:
Occasional to None

Duration:
Brief to None

Ponding:

Frequency:
None

Duration:
None

Runoff Class:
Low to Very high

Aspect:
Full range: 225-20-175
Central tendency: 285-20-75

Table 2. Representative physiographic features

Table 3. Representative physiographic features (actual ranges)

Climatic features

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 1,500 feet in the lower river valleys to 7,100 feet on the highest peaks. The annual precipitation increases from 17 inches in the valley to 40 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 = 75 to 115 days
Central tendency = 90 to 105 days

Mean annual precipitation (cm):
Total range = 280 to 1980 mm
(11 to 78 inches)
Central tendency = 590 to 1145mm
(23 to 45 inches)

MAAT (C)
Total range = 1.8 to 8.5
(35 to 47 F)
Central tendency = 4.2 to 5.9
(39 to 43 F)



Climate Stations:
Bonapart Stake

Influencing water features

Soil features

Representative Soil Features

This ecological site group is associated with several soil components. Most soil components can be grouped into six soil subgroups: Xeric Vitricryands, Haploxerandic Haplocryepts, Andic Dystrocryepts, Typic Haplocryands, Typic Vitricryands, and Vitrixerandic Haplocryepts. Most of these soils have developed in Mazama tephra deposits over till, outwash and residuum and colluvium from granitic and metamorphic rock. These tephra (ash) layers are important for forest productivity in that they retain large amounts of water compared to other parent materials, have high cation exchange capacity and high availability of organically bound plant nutrients. Minor amounts of soil are formed in lacustrine deposits. The soils range from moderately deep (densic contact) to very deep. Many of these soils have dense till layers at a depth of 20 to 40 inches and have a low available water holding capacity and slow to very slow permeability in the till layers. The soils are mostly moderately well drained to well-drained, though some poorly drained soils do occur. Surface textures include ashy silt loam, ashy loam, and ashy fine sandy loam.


Parent Materials:
Kind: Tephra (volcanic ash)
Origin: mixed
Kind: residuum, colluvium , alluvium
Origin: Granite, Metamorphic, Metasedimentary rock

Surface Texture:
(1)Ashy silt loam

(2) Ashy loam

(3) Ashy fine sandy loam

Subsurface Texture Group: Loamy

Surface Fragments: None

Drainage Class: Poorly to Well Drained
Permeability Class: Very Slow To Moderately rapid

Electrical Conductivity (mmhos/cm): 0-0-0


Sodium Absorption Ratio: 0-0-0


Calcium Carbonate Equivalent (percent): 0-0-10


Soil Reaction (1:1 Water): 5.3-6.3-7.9


Soil Reaction (0.01M CaCl2): NA


Available Water Capacity (inches):
3.4-6.2-10.9
(8.7-15.6-27.8cm)

Table 4. Representative soil features

Table 5. Representative soil features (actual values)

Other information

Overall this site is productive for tree species listed, however, cool air drainage and frosty conditions can create concerns for regeneration and optimum growth. Site indexes are measured on 50 year and 100 year tables based on Breast Height Age (BA) or Total Age (TA). CMAI indicates the sites ability to produce wood at a certain age of a stand’s maximum annual growth measured in cubic feet per acre.

Table 6. Representative site productivity

References

• . 1998. NRCS National Forestry Manual.

• Smith and Fischer. 1997. Fire Ecology of the Forest Habitat Types of Northern Idaho.

• Williams, C.K., B.F. Kelley, B.G. Smith, and T.R. Lillybridge. October, 1995. Forested Plant Associations of the Colville National Forest.

• Williams, C.K. and T.R. Lillybridge. 1983. Forested Plant Associations of the Okanogan National Forest R6-Ecol-132b-1983.

Approval

Kirt Walstad, 5/14/2024