Physiographic features

This ecological site occurs mainly on floodplains and stream terraces. Parent materials are volcanic ash and/or loess over mixed alluvium.

Landscapes: Plateaus, valleys, hill, foothills
Landforms: Flood plains, stream terraces, drainageways

Elevation:
Total range = 500 to 1230 m
(1,640 to 4,035 feet)
Central tendency = 775 to 955 m
(2,540 to 3,135 feet)

Slope (percent):
Total range = 0 to 4 percent
Central tendency = 0 to 2 percent

Water Table Depth: 0 – 77 cm (about 45% of components have a perched water table)
(0 - 30 inches)

Flooding:
Frequency: rare - frequent
Duration: brief – very long

Ponding:
Frequency: None
Duration: None

Aspect: NA

Table 2. Representative physiographic features

Table 3. Representative physiographic features (actual ranges)

Climatic features

The climate of this portion of the MLRA is controlled by a combination of large-scale and small-scale factors. The large-scale factors here include latitude, relative position on the North American continent, prevailing hemispheric wind patterns, and extensive mountain barriers. Small-scale or local factors include the topographic setting and position (valley, slope, or ridge location), as well as orientation or aspect, and vegetative cover. Elevation may cover various scales. Broadly, the climate is transitional between a northern Pacific coastal type and a continental type. The Pacific influence is noted particularly by the late autumn and winter maximum in cloudiness and precipitation; also in the relatively moderate average winter temperatures, compared with areas east of the Rocky Mountains. Summer is characteristically sunny and dry, though July and August are the only distinct summer months. July and August are thus also the peak fire-danger months. Annual precipitation (rain and melted snow) averages as little as 10 inches at the lowest canyon floors; over 100 inches at the highest elevations. Wettest months are normally November, December, and January. Close to 60 percent of the annual total occurs during the period November through March. A slight, secondary peak in precipitation normally appears in May and June, followed by a sharp decrease in July. Snowfall accounts for more than 50 percent of the total precipitation at elevations above 4,800 ft. Snow cover usually persists in the mid elevation valleys from early December through the end of March. High-elevation snowpack reaches a depth of 5 ft (1.5 m) or more in March and April and may linger into June. The main season of lightning (or thunderstorm) activity extends from late May through August. Storms occur on an average of 3 or 4 days each in June, July, and August. Monthly mean temperatures in populated valley locations range from 24 F (-4 C) in January to 65 F (18 C) in July; these are midpoint values between the average daily maximum and minimum temperatures. The annual mean is 43 F (6 C). A large diurnal range occurs in summer. Extreme temperatures have been as high as 103" to 105" F (about 40" C) and as low as -36" F (-38" C). Temperature inversions are commonplace, particularly on the clear summer and early autumn nights. The frost-free season, defined as the period with minimum temperatures staying above 32" F (0" C), varies widely with elevation and topographic position. The season is generally longer at lower elevation locations and on slope positions in the "thermal belt" around 3,500 ft. The season is shorter in positions affected by cold air drainage and slopes above the “thermal belt” at elevations >5,500 ft. Relative humidity is usually high throughout the day in late autumn and winter, averaging 70 to 80 percent or higher in midafternoon. In July and August, afternoon values average near 35 percent in the mid elevation valleys and 45 percent at 5,500 ft. Summer nighttime humidity in these valleys typically recovers to over 90 or 95 percent by dawn. On the slopes above the temperature inversion, at the same time, humidity may average only 50 to 60 percent. Winds have a prevailing (most frequent) direction from the southwest during all or most of the year. Local terrain effects modify the larger-scale wind that occurs in the adjacent free atmosphere. A nighttime drainage effect is common. Sunshine duration is at a minimum in December, when it may average only 20 percent of the maximum possible. July has close to 80 percent of the maximum possible.

(from Finklin, A. 1983. Climate of Priest River Experimental Forest, Northern Idaho.GTR-INT-159)

Frost-free period (days):
Total range = 63 to 134 days
Central tendency = 95 to 116 days

Mean annual precipitation (cm):
Total range = 515 to 1335 mm
(20 to 53 inches)
Central tendency = 750 to 990 mm
(30 to 39 inches)
MAAT (C)
Total range = 5.6 to 9.4
(42 to 49 F)
Central tendency = 7.1 to 8.0
(45 to 46 F)

Climate stations: none

Influencing water features

Soil features

This ecological site is associated with several soil components (Schnoorson, Lovell, Hoodoo, Porrett, Aquepts, Teneb, Lebaron, Clarkia, Aquolls, Potlatch, Cougarbay). These components can be grouped into the soil subgroups Aeric Fluvaquents, Aquandic Epiaqualfs, Aquandic Humaquepts, Aquandic Palexeralfs, Aquandic Endoaqualfs, Typic Vitraquands, Aquandic Albaqualfs, Fluvaquentic Endoaquolls. These soils are often composed volcanic ash and/or loess over mixed alluvium.

Parent Materials:
Kind: Tephra (volcanic ash)
Origin: mixed
Kind: loess
Origin: mixed
Kind: alluvium
Origin: mixed

Surface Texture:
(1) Ashy-Silt Loam
(2) Silt Loam
(3) Ashy-Loam
(4) Silty Clay Loam
(5) Ashy-Silty Clay Loam

Table 4. Representative soil features

Table 5. Representative soil features (actual values)

References

• . USNVC [United States National Vegetation Classification]. 2019. United States National Vegetation Classification Database, V2.03. Federal Geographic Data Committee, Vegetation Subcommittee, Washington DC.. USNVC: http://usnvc.org/.

• Finklin, A.I. 1983. Climate of Priest River Experimental Forest, northern Idaho. Gen. Tech. Rep. INT-159. U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station, Ogden, UT. 53.

• Jim Cornwell. 2009. NRCS Idaho Draft Range Site Descriptions.

• 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.

• Rocchio, J.F. and R.C. Crawford. 2015. Ecological systems of Washington State. A guide to identification. Washington Department of Natural Resources.. Natural Heritage Report.. Washington Department of Natural Resources, Natural Heritage Program, Olympia, WA. 1–397.

Contributors

Stephanies Shoemaker
Brian Gardner

Approval

Curtis Talbot, 10/15/2020