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): 044A-Northern Rocky Mountain Valleys
Modal LRU – 44A01 Spokane-Rathdrum Outwash Plains

This LRU is composed predominantly of low to mid elevation foothills and valley floors. The soils tend to be loamy andisols, mollisols and inceptisols with distinct or mixed ash surfaces. Till, outwash and residuum from granitic or metamorphic rock are the dominant parent materials. Soil climate is a mesic temperature regime and xeric moisture regime with average annual precipitation around 525 mm (21 inches).

Others where occurring – 44A02 - Pend Oreille-Kootenai Valleys
43A04 – Selkirk Mountains

Ecological Site Concept:

This ES group is distinguished by an overstory of grand fir and Douglas-fir and an understory shrub component of ninebark, oceanspray, snowberry and /or twinflower. It occurs on foothills, and terraces. This ES group fits into the National Vegetation Standard’s Grand Fir - Douglas-fir Central Rocky Mountain Forest & Woodland Alliance and Washington State’s Natural Heritage Program’s Northern Rocky Mt. Mesic Montane Mixed Conifer Forest.

Physiographic Features
Landscapes: Foothills, Valleys
Landform: outwash terraces, lake terraces and outwash plains

Elevation (m): Total range = 495 to 1185 m
(1,625 to 3,885 feet)
Central tendency = 645 to 860 m
(2,115 to 2,820 feet)

Slope (percent): Total range = 0 to 40 percent
Central tendency = 1 to 15 percent

Water Table Depth (cm):
40 cm to 75 cm (median = 53 cm)
(16 to 30 inches; median = 21 inches)

Flooding:
Frequency: None to occasional
Duration: None to brief


Ponding:
Frequency: None
Duration: None


Aspect: (central tendency)
119-202-287

Water Table Depth:
40 cm to >200 cm
(16 to >80 inches)

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 1,500 feet in the lower river valleys to over 7,000 feet in the higher terrain. The annual precipitation increases from 20 inches in the valleys to over 52 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 = 95 to 130 days
Central tendency = 110 to 120 days

Mean annual precipitation (cm): Total range = 355 to 1065 mm
(14 to 42 inches)
Central tendency = 555 to 760 mm
(22 to 30 inches)


MAAT (C): Total range = 4.8 to 9.3
(41 to 49 F)
Central tendency = 6.7 to 8.0
(44 to 46 F)

Climate Stations: CHEWELAH, CHEWELAH MTN LOOKOUT, Teepee Seed Orchard

Soil features

Representative Soil Features

This ecological site is associated with several soil soil series (e.g. Kegel, Mokins, Fan Lake, Dalkena, Wolfeson, Martella). The soil components can be grouped into: Fluvaquentic Haploxerolls, Andic Haploxeralfs, Vitrandic Haploxerepts, anmd Oxyaquic Vitrandic Haploxerepts. These soils have developed in thin or mixed Mazama tephra deposits over glaciolacustrine, outwash and alluvium from mixed sources. The soils are very deep and have adequate available water capacity to a depth of 1 m. The soils are mostly moderately well-drained.

Parent Materials:
Kind: Tephra (volcanic ash)
Origin: mixed
Kind: Till, Outwash
Origin: mixed
Kind: residuum and colluvium
Origin: Granite, Metasedimentary, other metamorphic rock

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

Surface Fragments

Vegetation dynamics

Ecological Dynamics of the Site

This site is the warmest extent where grand fir can be an overstory component. As the temperature gradient gets warmer Douglas-fir and ponderosa pine habitat types occur. Above this temperature gradient (cooler) subalpine fir habitats exist. Relative to moisture this is the driest grand fir habitat type. As moister increases grand fir/herb, cedar, and cedar-hemlock habitat types occur. Fire disturbance is a major factor in mature stand development. Frequent fires create an open stand of western larch, ponderosa pine, and Douglas-fir with a mixed understory of shrubs, grass, and herbs. Mixed severity fires create a patchy forest overstory with shrubs and grass understory. Fire exclusion allows grand fir to establish and become an overstory component with Douglas-fir. Stands in this condition are subject to stand replacing fires. Root rot can become a problem in these older stands dominated by Douglas-fir and grand fir.
The moister end of this ES lies in Northern Idaho where grand fir is more prominent in stand composition and western larch can be a major stand component. As this ES extends westward grand fir is near its ecological limit and is a minor stand component. Douglas-fir and ponderosa pine are the major tree species. In this warmer environment this ESG looks very similar to the Douglas-fir/ninebark ESG.

Major Land Resource Area

MLRA 044A
Northern Rocky Mountain Valleys

Subclasses

• F044AY503WA–Warm-Frigid, Moist- Xeric Loamy Foothills/Mountainsides, high water table (Grand Fir Warm Dry Shrub) Abies grandis - Pseudotsuga menziesii / Physocarpus malvaceus - Symphoricarpos albus

Stage

Provisional