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

This LRU is composed predominantly of low outwash terraces, outwash plains and the slopes of foothills or low mountains located south of the continental glacial margin and west of Lake Pend Oreille. The soils tend to be loamy andisols, mollisols and inceptisols with mixed to thick volcanic ash surfaces. Alluvium, till and outwash are the dominant parent materials. Soil climate is a mesic temperature regime and xeric moisture regime. Average annual precipitation around 525 mm (21 inches) and mean annual temperature of about 8.2 C (47 degrees F).

Ecological Site Concept:

The data below describes the physiographic, climatic and other parameters for the ponderosa pine/shrub ES group as a whole. This vegetation alliance is widespread so a Core Concept for each parameter is also described. See Appendix A for a finer division of the alliance based on selected soil features.

This ESD in distinguished by an overstory of ponderosa pine understory shrub component of ninebark, oceanspray, and snowberry. It occurs on foothills, mountainsides, and flat terraces. This ESD fits into the National Vegetation Standard’s Central Rocky Mt. Pinus ponderosa / Shrub Understory alliance.

Physiographic Features

This ecological site group occurs mainly on low to mid elevation slopes of glaciated foothills and outwash valleys. It is found predominantly on side slopes, foot slope, and flats. The parent material is volcanic ash or mixed volcanic ash and loess over till, loamy outwash or residuum and colluvium from mainly granitic and metasedimentary rock.


Landscapes: Foothills, Valleys
Landform: Hill slopes, Outwash Terraces, Outwash Plains



Elevation:
Total range = 375 to 870 m
(1,230 to 2,855 feet)
Core Concept = 560 to 685 m
(1,835 to 2,250 feet)

Slope (percent):
Total range = 0 to 45 percent
Core Concept = 6 to 25 percent

Water Table Depth:
56 cm to >200 cm (>85% have no water table present)
(22 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 1,000 feet in the lower river valleys to 3,400 feet over the higher terrain. The annual precipitation increases from 18 inches in the valley to 24 inches over the higher foothills. 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 = 105 to 140 days
Core Concept = 120 to 130 days

Mean annual precipitation (cm):
Total range = 240 to 640 mm
(9 to 25 inches)
Core Concept = 390 to 490 mm
(15 to 19 inches)

MAAT (C)
Total range = 6.9 to 10.2
(44 to 50 F)
Core Concept = 8.1 to 8.9
(47 to 48 F)



Climate Stations: none

Soil features

Representative Soil Features

This ecological site group is associated with several soil components. The soil components can be grouped into two soil subgroups: Vitrandic Haploxerolls, and Vitrandic Haploxerepts. Most of these soils have developed in till, outwash and residuum and colluvium from granitic and metasedimentary rock with mixed volcanic ash in the surface. Minor amounts of soil are formed in lacustrine deposits. The soils range from shallow (lithic bedrock) to very deep. Many of these soils have dense till layers at a depth of 20 to 40 inches and have a low available water holding capacity and slow to very slow permeability in the till layers. The soils are mostly well-drained. Surface textures include ashy fine sandy loam, gravelly ashy sandy loam, stony and/or very stony ashy sandy loam.

See appendix A for a discussion of different sub-divisions of the ponderosa pine/shrub alliance based on differences in soils features.

Appendix A

Examination of map unit components assigned to the Ponderosa Pine/ Shrub alliance showed two possible subdivisions of the larger ecological group.

These are:
1) Warm Mesic Xeric Loamy Foothills, Terraces, low AWC subsoils (Ponderosa Pine/Shrub)
2) Warm Mesic Xeric Sandy Hill slopes and Outwash terraces (Ponderosa Pine/Shrub)


A.1 Warm Mesic Xeric Loamy Foothills, Terraces, low AWC subsoils (Ponderosa Pine/Shrub)

Found in LRU 44A01 (Spokane-Rathdrum Outwash Plain). Climate parameters were obtained from PRISM and other models for the area. Landscape descriptors are derived from USGS DEM products and their derivatives.

Physiographic Features
Landscapes: Foothills, Valleys
Landform: sideslopes, foot slopes summits

Elevation (m): Total range = 490 to 880 m
(1,610 to 2,885 feet)
Core Concept = 635 to 730 m
(2,085 to 2,395 feet)

Slope (percent): Total range = 0 to 55 percent
Core Concept = 8 to 25 percent

Water Table Depth (cm): none present

Flooding:
Frequency: None
Duration: None

Ponding:
Frequency: None
Duration: None

Aspect: 60-165-345
Core Concept: 100-165-260

Climatic Features
Frost-free period (days): Total range = 105 to 135 days
Core Concept = 120 to 125 days

Mean annual precipitation (cm): Total range = 380 to 665 mm
(15 to 26 inches)
Core Concept = 425 to 520 mm
(17 to 20 inches)

MAAT (C): Total range = 7.3 to 9.6 C
(45 to 49 F)
Core Concept = 8.2 to 8.8 C
(47 to 48 F)

Climate Stations: none

Representative Soil Features

This ecological subsite is associated with several soil series (e.g.). The soils are Bobbitt, Lenz, McGuire, Northstar, Skalan, Spokane. The soil components can be grouped into four soil subgroups: Typic Xerochrepts, Ultic Haploxeralfs, Vitrandic Argixerolls, Vitrandic Haploxerolls. These soils have developed in Mazama tephra deposits and loess mixed with outwash, colluvium, and residuum, from granitic, basalt, metamorphic and other mixed rock. The soils are predominantly moderately deep and have a no water table within 75cm of the surface during any part of the year. The soils are mostly well drained.

Parent Materials:
Kind: Tephra (volcanic ash)
Origin: mixed
Kind: outwash, colluvium, residuum, loess
Origin: granitic, basalt, metamorphic, other unspecified

Surface Texture:
(1) Ashy Loam
(2) Ashy Sandy Loam

Fragment content of surface (hard fragments): 0 to 29 percent (median = 0%)

Subsurface Texture Group: Loamy
Fragment content of subsurface (25 to 100cm): 0 to 80 percent (median = 55%)
Most components lack surface fragments
Drainage Class: Well drained (small number Somewhat Excessively drained)
Saturated Hydraulic conductivity: Moderately High to Very High (above restriction) (median = High)
Soil Depth: 66 to >200 cm (median = 81cm)
Lithic contact – 66-97 cm
Paralithic contact – 66 cm
Calcium Carbonate Equivalent (percent): 0
Soil Reaction (1:1 Water): 5.0 to 7.0
Available Water Capacity (total in 100cm): 4.24-6.68cm (median = 5.69cm)


A.2 Warm Mesic Xeric Sandy Hill slopes and Outwash terraces (Ponderosa Pine/Shrub)

Found in LRU 44A01 (Spokane-Rathdrum Outwash Plain). Also present in 43A03 (Columbia-Colville Valleys). Climate parameters were obtained from PRISM and other models for the area. Landscape descriptors are derived from USGS DEM products and their derivatives.

Physiographic Features
Landscapes: Foothills, Valleys
Landform: sideslopes, foot slopes, toe slopes, summits and flats

Elevation (m): Total range = 490 to 880 m
(1,610 to 2,885 feet)
Core Concept = 635 to 730 m
(2,085 to 2,395 feet)

Slope (percent): Total range = 0 to 55 percent
Core Concept = 8 to 25 percent

Water Table Depth (cm): none present

Flooding:
Frequency: None
Duration: None

Ponding:
Frequency: None
Duration: None

Aspect: 60-165-345
Core Concept: 100-165-260

Climatic Features
Frost-free period (days): Total range = 105 to 135 days
Core Concept = 120 to 125 days

Mean annual precipitation (cm): Total range = 380 to 665 mm
(15 to 26 inches)
Core Concept = 425 to 520 mm
(17 to 20 inches)

MAAT (C): Total range = 7.3 to 9.6 C
(45 to 49 F)
Core Concept = 8.2 to 8.8 C
(47 to 48 F)

Climate Stations: none

Representative Soil Features

This ecological subsite is associated with several soil series (e.g.). The soils are Hallcreek, Spokane, Springdale. The soil components can be grouped into two soil subgroups: Andic Haploxerepts, and Vitrandic Haploxerepts. These soils have developed in Mazama tephra deposits and loess mixed with outwash, colluvium, and residuum, from granitic, basalt, metamorphic and other mixed rock. The soils are predominantly moderately deep and have a no water table within 75cm of the surface during any part of the year. The soils are mostly well drained.

Parent Materials:
Kind: Tephra (volcanic ash)
Origin: mixed
Kind: outwash, loess
Origin: mixed unspecified

Surface Texture:
(1) Ashy Coarse Sandy Loam
(2) Ashy Sandy Loam

Fragment content of surface (hard fragments): 0 to 27 percent (median = 24%)

Subsurface Texture Group: Loamy
Fragment content of subsurface (25 to 100cm): 23 to 77 percent (median = 41%)
Most components lack surface fragments
Drainage Class: Somewhat Excessively drained
Saturated Hydraulic conductivity: High to Very High (median = High)
Soil Depth: >200 cm
Calcium Carbonate Equivalent (percent): 0
Soil Reaction (1:1 Water): 5.0 to 6.7
Available Water Capacity (total in 100cm): 4.17-7.10cm (median = 4.35cm)

Vegetation dynamics

This site is located level terrain, foot slopes and side slopes. It is on sites with more moisture than the pine/dry shrub or pine/dry grass sites. Most of this site occurs under 2500’ of elevation. Reference state is characteristic of mature pine stands over snowberry, serviceberry, spirea, chokecherry, woods rose, nutka rose, cascara and ninebark. Redstem ceanothus may be present as evidence of past fires. Fire disturbance is sporadic and currently in the mixed severity or stand replacing regimes. It would not be considered in the pine/savanna category due to lack of frequent ground fires. Overstory canopy cover of these mature pine stands will range from 40 – 60%. These mature pine stands will be subject to bark beetle kill, windfall, and fire. The understory shrubs will resprout quickly and pine regeneration will be dependent on pine seed placement and shrub competition.
The pine/snowberry plant association will be located on the drier topographic locations and the pine/ninebark plant association will be located on northern aspects. These sites have been subject to overgazing, introduced grass seeding and land conversion. Kentucky bluegrass and Canada bluegrass have invaded many of these sites dominating the understory. Sites on level terrain have been converted to crops, pasture, or urban land.

Relationship to Other Established Classifications:

United States National Vegetation Classification (2008) – A3446 Ponderosa Pine / Shrub Understory Central Rocky Mt. Forest & Woodland Alliance

Washington Natural Heritage Program. Ecosystems of Washington State, A Guide to Identification, Rocchio and Crawford, 2015 – Northern Rocky Mountain Ponderosa Pine Woodland and Savanna

Description of Ecoregions of the United States, USFS PN # 1391, 1995 - M333 Northern Rocky Mt. Forest-Steppe-Coniferous Forest-Alpine Meadow Province

Level III and IV Ecoregions of WA, US EPA, June 2010 - 15r Okanogan – Colville Xeric Valleys & Foothills and 15s Spokane Valley Outwash Plains

This ecological site includes the following USDA Forest Service Plant Associations: PIPO/SYAL, PIPO/PHMA, and PIPO/SYOR. (Williams et. al. 1995)

Major Land Resource Area

MLRA 044A
Northern Rocky Mountain Valleys

Subclasses

• F044AY501WA–Warm Mesic Xeric Loamy Foothills, Terraces, low AWC subsoils (Ponderosa Pine/Shrub) Pinus Ponderosa /Symphoricarpos albus, Pinus Ponderosa / Physocarpus malvaceus
• F044AY502WA–Warm Mesic Xeric Sandy Hill slopes and Outwash terraces (Ponderosa Pine/Shrub) Pinus Ponderosa /Symphoricarpos albus, Pinus Ponderosa / Physocarpus malvaceus

Stage

Provisional