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

Major land resource area (MLRA): 043A-Northern Rocky Mountains
Modal LRU – 43A01 Okanogan Plateau

This LRU is composed predominantly of mid to low elevation mountain slopes, foothills, structural benches and valley walls. The soils tend to be loamy andisols, or inceptisols and mollisols with distinct ash surfaces. Till, outwash and residuum/colluvium from granitic or metamorphic rock are the dominant parent materials. Soil climate is a frigid or cryic temperature regime and xeric moisture regime with average annual precipitation around 535 mm (21 inches).

Others where occurring – 43A02 – Western Selkirk Highlands
43A03 – Columbia-Colville Valleys
44A02 - Pend Oreille-Kootenai Valleys


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

Landscapes: Mountains, Valleys

Landforms: Mountain slopes, Outwash Terraces, Lacustrine Terraces, Till plains, and Moraines

Elevation:
Total range = 370 to 805 m
(1,215 to 2,640 feet)
Central tendency = 535 to 650 m
(1,755 to 2,130 feet)

Slope (percent):
Total range = 0 to 50 percent
Central tendency = 10 to 30 percent

Water Table Depth:
70 to >200 cm (where present water tables are perched)
(28 to >80 inches)



Flooding:

Frequency: None
Duration: None

Ponding:

Frequency: None
Duration: None

Aspect: 330-20-120 (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 1,205 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 125 days
Central tendency = 100 to 110 days

Mean annual precipitation (cm):
Total range = 370 to 805 mm
(15 to 32 inches)
Central tendency = 535 to 650 mm
(21 to 26 inches)
MAAT (C)
Total range = 3.5 to 8.2
(38 to 48 F)
Central tendency = 5.3 to 6.5
(41 to 44 F)

Climate stations: AENEAS LOOKOUT, IRENE MTN WAUCONDA, KETTLE FALLS, QUARTZ LOOKOUT, Lost Lake

Soil features

Representative Soil Features

This ecological site is associated with several soil components. The soil components can be grouped into seven soil suborders. These are the Andic Haploxeralfs, Andic Haploxerepts, Typic Vitrixerands, Vitrandic Haploxeralfs, Vitrandic Haploxerepts, Vitrandic Haploxerolls, and Xeric Vitricryands. 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 granitic or metamorphic 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, Galciolacustrine
Origin: mixed
Kind: residuum and colluvium
Origin: Granitic, Metavolcanic

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

Surface Fragments

Vegetation dynamics

Ecological Dynamics of the Site
This ecological site is a combination of two plant associations Douglas-fir / dwarf huckleberry and Grand fir (ABGR) / dwarf huckleberry. A close plant association in the Okanogan region is the Douglas-Fir (PSME)/huckleberry plant association. Most of the PSME/cool shrub is located west of the Columbia river and the ABGR/cool shrub occurs east of the Columbia River. They both occur on low benches and outwash terraces. They are situated on cool air drainages creating frosty conditions. They are warm during the day and cool at night when the cool air drains in. Elevations range is 2000 - 4000 feet. They are similar ecologically with the difference being the DF/dwarf huckleberry is drier with no grand fir and ponderosa pine more consistent on the Douglas-fir site. They both have Douglas-fir, lodgepole pine (PICO), and western larch (LAOC) as main components of seral and mid seral stands. Both rarely reach climax condition with grand fir as the main overstory stand component due to fire or human disturbance. The grand fir site is more productive for tree growth with higher site indices for all species.

Douglas-fir is the main tree component with western larch, lodgepole pine, and ponderosa pine (PIPO) (sporadic depending on frost). Grand fir will be minor component in the understory. Englemann spruce (PIEN) may be present on moist sites. Dwarf huckleberry is the key understory component along with bearberry, shiny-leaf spirea, serviceberry, twinflower, snowberry, pachistima, Utah honeysuckle, Oregon Grape, pinegrass, heartleaf arnica, feather solomonplume, and w. prince’s pine. In the moister grand fir portions of this site bunchberry dogwood, queencup beadlily, baldhip rose, russet buffaloberry, and western fescue can be present.

Major Land Resource Area

MLRA 043A
Northern Rocky Mountains

Subclasses

• F043AY531WA–Cool-Frigid, Moist-Xeric, Loamy Mountainsides, ashy surface (Douglas-fir-Grand Fir Cool Shrub) Douglas-fir-grand fir/low huckleberry-big huckleberry-dwarf huckleberry
• F043AY532WA–Cool-Frigid, Moist-Xeric, Loamy Terraces, ashy surface (Douglas-fir-Grand Fir Cool Shrub) Douglas-fir-grand fir/low huckleberry-big huckleberry-dwarf huckleberry

Stage

Provisional