Physiographic features

Physiographic Features
This ecological site occurs mainly on forested footslopes of mountains, floodplains, backswamps, drainageways and depressions on terraces or valley floors. Parent materials are alluvium or till derived from mixed origins mantled by mixed volcanic ash and loess.

Landscapes: Mountains, Valleys

Landforms: Mountain foot slopes, drainageways, flood plains, backswamps,
stream terraces, valley floors

Elevation:
Total range = 440 to 1450 m
(1.445 to 4,755 feet)
Central tendency – 620 to 950 m
(2,035 to 3,115 feet)

Slope (percent):
Total range = 0 to 33 percent
Central tendency = 0 to 13 percent

Aspect: all

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 = 85 to 145 days
Central tendency = 105 to 120 days

Mean annual precipitation (cm):
Total range = 285 to 1225 mm
(11 to 48 inches)
Central tendency = 375 to 715 mm
(15 to 28 inches)

MAAT (C)
Total range = 3.5 to 9.8
(38 to 50 F)
Central tendency = 6.4 to 8.3
(43 to 47 F)

Climate stations: none

Influencing water features

Water Table Depth:
0 - 62 cm
(0 - 24 inches)

Flooding:
Frequency: None to Frequent
Duration: None to Long

Ponding:
Frequency: None to Frequent
Duration: None to Long

Soil features

Representative Soil Features

This ecological site is associated the soil components Aquandic Endoaquolls, Bossburg, Longswamp, Medisaprists, Ralsen, Sanpoil, and Uncas. These components are Aquandic Endoaquolls, Cumulic Haplaquolls, Fluvaquentic Haplaquolls, Histic Vitraquands, and Vitrandic Haploxerolls. These soils have developed in mixed Mazama tephra deposits over alluvium or 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.

Table 4. Representative soil features

Table 5. Representative soil features (actual values)

References

• Kovalchik, B.L. and R.R. Clausnitzer. 2004. Classification and Management of Aquatic, Riparian, and Wetland Sites on the National Forests of Eastern Washington: Series Description. General Technical Report PNW-GTR-593. United States Department of Agriculture, Forest Service, Pacific Northwest Research Station. 1–354.

• 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, 10/14/2020