Physiographic features

Physiographic Features
This ecological site occurs mainly on forested backslopes of mountains and side slopes of associated drainageways. Parent materials are till derived from mixed origins thinly mantled by mixed volcanic ash and loess.

Landscapes: Mountains

Landforms: Mountain slope, drainageways

Elevation:
Total range = 915 to 1675 m; median = 1235 m
(3,000 to 5,495 feet; median = 4,050 feet)

Slope (percent):
Total range = 3 to 65 percent
Median = 25 percent

Water Table Depth:
90-170 cm
(35-70 inches)

Flooding:

Frequency: None
Duration: None

Ponding:

Frequency: None
Duration: None

Aspect: 248-23-113

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 1,205 feet in the lower river valleys to over 7,200 feet in the higher terrain. The annual precipitation increases from 14 inches in the valleys to over 45 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 = 70 to 120 days
Median = 115 days

Mean annual precipitation (cm):
Total range = 355 to 760 mm
(14 to 30 inches)
Median = 480 mm
(19 inches)
MAAT (C)
Total range = 2.8 to 6.7
(37 to 44 F)
Median = 5.6
(42 F)

Climate stations: none

Influencing water features

Water Table Depth:
90-170 cm
(35-70 inches)

Soil features

Representative Soil Features

This ecological site is associated the soil component Koepke . This component is Vitrandic Haploxerolls. These soils have developed in mixed Mazama tephra deposits over glacial till. The tephra influenced 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,
Origin: mixed

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

Surface Fragments

Table 4. Representative soil features

Table 5. Representative soil features (actual values)

References

• 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

Curtis Talbot, 10/23/2020