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

Hierarchical Classification
Major Land Resource Area (MLRA): 6 – Cascade Mountains, East Slope

LRU – Common Resource Areas (CRA):
6.5 – Chiwaukum Hills and Lowlands
6.6 – Yakima Plateau and Slopes
6.7 – Grand Fir Mixed Forest
6.8 – Oak-Conifer Eastern Cascades-Columbia Foothills


Site Concept Narrative:
Diagnostics:

More than 80% of the landscape of MLRA 6 is forest. This site stands out because of a lack of trees.

North Aspect, prairie is an upland ecological site on the prairie portion of MLRA 6 – the High Prairie in Klickitat County and the Swauk Prairie in Kittitas County. This site occurs on north-facing slopes. The soils are silt loam over gravelly clay loam and deeper than 40 inches. North Aspect Prairie soils are not hydric.

In the Reference State North aspect, prairie has a dense herbaceous layer with little bare ground and not much lichen-moss.

The High Prairie and the Swauk Prairie are grassland steppe and do not have sagebrush, nor bitterbrush, and no rabbitbrush. Bitterbrush may be found on adjoining ecological sites, however. Idaho fescue dominates the reference state in terms of cover and production. Other native bunchgrasses and native forbs fill the interspaces.


Principle Vegetative Drivers:

The vegetative expression of this productive site is driven by three factors: (1) moderately deep to deep soil depth provides unrestricted rooting for most species, (2) precipitation of 20-24 inches ensures a long growing season, and (3) the north aspect provides cooler temperatures year-round and longer lasting snowpack than adjacent ecological sites. North Slope provides crucial water to Idaho fescue at the hottest time of the growing season. Also, being wetter, North Slope supports a denser plant cover than the Loamy Prairie ecological site.


Influencing Water Features:

A plant’s ability to grow on a site and overall plant production is determined by soil-water-plant relationships
1. Whether rain and melting snow runs off-site or infiltrates into the soil
2. Whether soil condition remain aerobic or become saturated and become anaerobic
3. Water drainage and how quickly the soil reaches wilting point

This ecological site is cooler and moister than surrounding sites due to microclimatic effects. North slopes have less direct solar radiation and reduced evapotranspiration than adjacent uplands or south facing slopes and may retain snow cover longer into the growing season. Deep soils on the north slopes and extensive subsurface root systems of the dominant grasses also provide greater soil moisture infiltration and retention compared with other areas.

Compared to other upland ecological sites, North Slope has more available soil moisture. The north and northeast slopes mean cooler temperatures. Closer spacing of plants mean less evaporation and less runoff. Idaho fescue is especially linked to the additional soil moisture on this ecological site. Bluebunch wheatgrass, is not as linked to the additional soil moisture.


Physiographic Features:

Most of MLRA 6 is in the Northern and Middle Cascade Mountains. This mountainous area consists of sharp alpine summits with some higher volcanic cones to the west, and lower lying foothills to the east. Strongly sloping mountains and U-shaped valleys are dominant in the north, with eroded basalt plateaus more typical in the south. The East Slope of the Cascades is a transitional area between the moist, rugged Cascade Mountains to the west and the drier, lower lying Columbia Basalt Plateau to the east. MLRA 6 has some of the landforms typical of both mountains and plateaus.

Physiographic Division: Pacific Mountains
Physiographic Province: Cascade-Sierra Mountains
Physiographic Sections: Northern Cascade and Middle Cascade Mountains

Landscapes: Mountains and hills
Landform: Side-slopes, summits and shoulders

Elevation: Dominantly 2,000 to 5,500 feet
Central tendency: 2,800 to 4,800 feet
Slope: Total range: 0 to 60 percent
Central tendency: 2 to 30 percent
Aspect: Dominantly northerly aspects, but occurs on all aspects


Geology:

MLRA 6 consists of Pre-Cretaceous metamorphic rocks cut by younger igneous intrusives. Tilted blocks of marine shale, carbonate, and other sediments occur in the far north, and some younger continental, river-laid sediments occur around Leavenworth, WA. Columbia River basalt is dominant in the southern portion of the state. Alpine glaciation has left remnants of glacial till, debris, and outwash in the northern part of this MLRA.

Climate

The climate across MLRA 6 is characterized by moderately cold, wet winters, and hot, dry summers, with limited precipitation due to the rain shadow effect of the Cascades. The average annual precipitation for most of the East Slope of the Cascades is 16-50 inches. Seventy-five to eighty percent of the precipitation comes late October through March as a mixture of rain and snow. The lowest precipitation occurs along the eastern edge, then increasing with rising elevation to the west. Most of the rainfall occurs as low-intensity, Pacific frontal storms during the winter, spring and fall. Rain turns to snow at the higher elevations. All areas receive snow in winter. Summers are relatively dry. The East Slopes experience greater temperature extremes and receive less precipitation than the west side of the Cascades. The shortest freeze-free periods occur along the western edge and the northern end of this MLRA, which are mountainous. The longest freeze-free periods occur along the Columbia River Gorge.

Mean Annual Precipitation:
Range: 18-40 inches
Central tendency: 20-24 inches
Soil moisture regime is xeric.

Mean Annual Air Temperature:
Range: 43 to 48 degrees
Central tendency: 44 to 46 degrees
Soil temperature regime is mesic to frigid.

Frost-free period (days):
Total range: 40 to 130
Central tendency: 70 to 110
The growing season for North aspect, prairie is March through mid-August.

Soil features

Edaphic:

This North aspect, prairie occurs with Loamy, prairie, Shallow stony, prairie and Very shallow ecological sites.


Representative Soil Features:

This ecological site components are dominantly Vitrandic and Ultic taxonomic subgroups of Argixerolls and Haplocryolls great groups of the Mollisols. Soils are dominantly moderately deep or deeper. Average available water capacity of about 4.0 inches (10.2 cm) in the 0 to 40 inches (0-100 cm) depth range.

Soil parent material is dominantly mixed loess and colluvium over residuum.

The associated soils are Sapkin and similar soils.

Dominate soil surface is loam to very stony loam.

Dominant particle-size class is loamy to loamy skeletal.

Fragments on surface horizon > 3 inches (% Volume):
Minimum: 0
Maximum: 5
Average: 1

Fragments within surface horizon > 3 inches (% Volume):
Minimum: 10
Maximum: 35
Average: 30

Fragments within surface horizon ≤3 inches (% Volume):
Minimum: 0
Maximum: 20
Average: 10

Subsurface fragments > 3 inches (% Volume):
Minimum: 5
Maximum: 30
Average: 20

Subsurface fragments ≤ 3 inches (% Volume):
Minimum: 10
Maximum: 30
Average: 15

Drainage Class: Dominantly well drained
Water table depth: Greater than 20 inches

Flooding:
Frequency: None

Ponding:
Frequency: None

Saturated Hydraulic Conductivity Class:
0 to 10 inches: Moderately high and high
10 to 40 inches: Moderately high to low

Depth to root-restricting feature (inches):
Minimum: 30
Maximum: Greater than 60

Electrical Conductivity (dS/m):
Minimum: 0
Maximum: 0

Sodium Absorption Ratio:
Minimum: 0
Maximum: 0

Calcium Carbonate Equivalent (percent):
Minimum: 0
Maximum: 0

Soil Reaction (pH) (1:1 Water):
0 - 10 inches: 6.1 to 7.3
10 - 40 inches: 6.1 to 7.3

Available Water Capacity (inches, 0 – 40 inches depth):
Minimum: 1.3
Maximum: 5.0
Average: 4.0

Vegetation dynamics

Ecological Dynamics:

North Aspect, prairie produces about 1000-1400 pounds/acre of biomass annually

In the reference condition Idaho fescue dominates the North aspect, prairie ecological site. Idaho fescue is a long-lived shorter grass and has a dense clump of shoots. Idaho fescue has an awned panicle inflorescence.

Idaho fescue provides a crucial and extensive network of roots to the upper portions (up to 48” deep in soils with no root-restrictive horizons) of the soil profile. These roots create a massive underground source to stabilize the soils, provide organic matter and nutrients inputs, and help maintain soil pore space for water infiltration and water retention in the soil profile. The extensive rooting system of mid-sized bunchgrasses leave very little soil niche space available for invasion by other species. This drought resistant root can compete with, and suppress, the spread of exotic weeds.

The stability and resiliency of the reference communities is directly linked to the health and vigor of Idaho fescue. Research has found, on similar rangeland, that communities remain resistant to medusahead if sites maintain at least 0.8 mid-sized bunchgrass plant/sq. ft. (K. Davies, 2008). Idaho fescue holds the system together. If we lose either or both bunchgrass the ecosystem begins to unravel.

The natural disturbance regime for grassland communities is periodic lightning-caused fires. Ponderosa pine communities have the shortest FRI of about 10-20 years (Miller). The FRI increases as one moves to wetter forested sites or to dries shrub steppe
communities. Given the uncertainties and opinions of reviewers, a mean of 75 years was chosen for Wyoming sagebrush communities (Rapid Assessment Model). This would place the historic FRI for prairies around 30-50 years perhaps, and even as short as 5-10 years in some locations.

The effect of fire on the community depends upon both the severity and season of the burn. See Vallentine’s Range Improvement for more detail. With a light to moderate fire there can be a mosaic of burned and unburned patches. Bunchgrasses thrive as the fire does not get into the crown. Idaho fescue can exhibit rapid tillering when there is light severity fires and favorable soil moisture. Largely, the community is not affected by lower intensity fire

A severe fire puts stress on the entire community. Some spots and areas can be completely sterilized. Under windy conditions, a fire can burn into the crown of Idaho fescue, leaving behind “black holes” or nothing but ash where fescue plants were incinerated. Sterilized spots and dead Idaho fescue plants makes the site vulnerable to exotic invasive species, so seeding should be strongly be considered. Idaho fescue makes the site more at risk.

Spring burning can be especially damaging to Idaho fescue.

Grazing is another common disturbance that occurs to this ecological site. Grazing pressure can be defined as heavy grazing intensity, or frequent grazing during reproductive growth, or season-long grazing (the same plants grazed more than once). As grazing pressure increases the plant community unravels in stages:
1. Idaho fescue declines while bluebunch wheatgrass and unpalatable forbs increase
2. All grasses decline while unpalatable forbs continue to increase. Invasive species such as bulbous bluegrass, annual bromes and ventenata colonize the site
3. The site can become an invasive grass community

Managing grassland to improve the vigor and health of native bunchgrasses begins with an understanding of grass physiology. New growth each year begins from basal buds. Given the opportunity Idaho fescue readily produces new seedlings while bluebunch wheatgrass plants rely principally on tillering. During seed formation, the growing points of bluebunch wheatgrass become elevated and are vulnerable to damage or removal. Idaho fescue has weak stems and is much more sensitive to grazing than bluebunch wheatgrass.

If defoliated during the formation of seeds, bluebunch wheatgrass has limited capacity to tiller compared with other, more grazing resistant grasses (Caldwell et al., 1981). Repeated critical period grazing (boot stage through seed formation) is especially damaging. Over several years each native bunchgrass pasture should be rested during the critical period two out of every three years (approximately April 15–July 15). And each pasture should be rested the entire growing-season every third year (approximately March 1 – July 15).

In the spring each year it is important to monitor and maintain an adequate top growth: (1) so plants have enough energy to replace basal buds annually, (2) to optimize regrowth following spring grazing, (3) to protect the elevated growing points of bluebunch wheatgrass, and (4) to avoid excessing defoliation of Idaho fescue with its weak stems.

These grasses remain competitive if:
(1) Basal buds are replaced annually,
(2) Enough top-growth is maintained for growth and protection of growing points,
(3) Idaho fescue makes viable seed and
(4) The timing of grazing and non-grazing is managed over a several-year period. Careful management of late spring grazing is especially critical

For more grazing management information refer to Range Technical Notes found in Section I Reference Lists of NRCS Field Office Technical Guide for Washington State.

In Washington, Idaho fescue – bluebunch wheatgrass communities provide habitat for a variety of upland wildlife species.


Supporting Information:

Associated Sites:
North Aspect, prairie is associated with Loamy prairie, Shallow Stony prairie and
Very Shallow ecological sites.

Similar Sites:
North Aspect, prairie is similar to North Aspect in MLRA 8 for the Goldendale Prairie

Inventory Data References (narrative):
Data to populate Reference Community came from several sources: (1) NRCS ecological sites from 2004, (2) Soil Conservation Service range sites from 1980s and 1990s, (3) Daubenmire’s habitat types, and (4) ecological systems from Natural Heritage Program

Major Land Resource Area

MLRA 006X
Cascade Mountains, Eastern Slope

Stage

Provisional

Contributors

Provisional Site Author: Kevin Guinn Technical Team: R. Fleenor, K. Bomberger, K. Paup-Lefferts