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): 9 – Palouse and Nez Perce Prairie

LRU – Common Resource Areas (CRA):
9.1 - Channeled Scablands
9.12 - Moist Loess Islands
9.2 - Palouse Hills
9.3 - Dissected Loess Uplands
9.4 - Deep Loess Foothills
9.5 - Warm Canyons and Dissected Uplands

Site Concept Narrative:
Diagnostics:

Very Shallow is a sparsely vegetated, upland site on very shallow soils (generally less than 8 inches deep). Very shallow sites are often found on windswept ridges and adjacent to exposed rocky ledges. Daubenmire writes that there appears to be no regular difference in either soils or vegetation between lithosols produced by glaciofluvial erosion or those on ridges where only wind and rain could have kept the basalt exposed.

Generally, there are sharp lines on the landscape between Very Shallow and the adjacent ecological site.

Very Shallow expresses itself in four different variations in MLRA 9, all with very low production. This site can be low shrub-short grass, short grass, short grass-short grass or mid grass-short grass. Only in the Channeled Scabland will the stiff sagebrush-Sandberg bluegrass community be found. The Sandberg bluegrass and Sandberg bluegrass-one-spike oatgrass variation are plant communities with mainly short grasses. Likely associated with fracturing in the basalt is the last variation, bluebunch wheatgrass-Sandberg bluegrass.

While there are minor ecological differences between these variations, they are considered functionally equivalent for the purposes of this ecological site. These variations have been combined into one ecological site for several reasons: (1) the co-dominant short grass is Sandberg bluegrass in all cases, (2) Very Shallow has low plant productivity and extreme site limitations. (3) it is common to find three or more of these low shrub or forb species on the same site, and (4) the hydrologic and watershed characteristics is similar regardless of low shrub.

According to Daubenmire, stiff sagebrush is limited to basalts with highly fractured parent material. On some but not all Very Shallow sites, are a few micro-pockets of taller vegetation in association with bedrock fracturing. Taller vegetation can be bluebunch wheatgrass for example.

Many Very Shallow sites in MLRA 9 have ventenata. During wet years Very Shallow can look like a sea of ventenata, but in normal or dry years looks like classic Very shallow with only a thin scattering of ventenata.

Usually, there are abundant rock and soil biotic crust cover, in the interspaces between plants. The lichen and moss play a critical role in water infiltration and resistance to erosion. Because soil depth in minimal, Very Shallow can be seasonally saturated, and heavy traffic (or trailing) can form erosive ruts.

Principle Vegetative Drivers:

The very shallow soil depth and the fracturing of, or the lack of fracturing in the underlying basalt bedrock drive the vegetative expression of this site. Deep-rooted steppe species do not grow on very shallow because of the limited soil depth. The fracture system accounts for variation in the low shrub component and the occasional mid-sized bunchgrass such as bluebunch wheatgrass.

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

The lower part of the soil profile of Very Shallow has high clay content. With winter rain and melting snow, water perches and creates saturated conditions.

In wet years during spring runoff, water runs on the surface of Very Shallow sites for a short period. Even more water runs beneath the surface to sites below. This increases the effective precipitation to the adjacent sites below.

Physiography:

MLRA 9 is south of the Okanogan Highlands and Spokane Valley, east of the Columbia Basin, includes only the wet end of the Channeled Scablands and forms a horseshoe around the Blue Mtns. The landscape is part of the Columbia basalt plateaus and Northern Rocky foothills. Did not come up with a convenient elevational line.

MLRA 9 has three distinct geographical types:
(1) the Palouse Hills on the east side
(2) the loess hills to the south and west
(3) the Channeled Scabland-loess islands in the northwest

Physiographic Division: Intermontane Plateau and Northern Rocky Mountain System
Physiographic Province: Columbia Plateau and Northern Rocky Mountains
Physiographic Sections: Walla Walla Plateau and Blue Mountain Section

Landscapes: Hills, plateaus and mountains
Landform: Sideslopes, hillslopes, ridges

Elevation: Dominantly 1,000 to 5,500 feet
Slope: Total range: 0 to 90 percent
Central tendency: 20 to 50 percent
Aspect: Occurs on all aspects

Geology:

MLRA 9 is almost entirely underlain by Miocene basalt flows. Columbia River basalts are covered by wind-blown loess and volcanic ash with a thickness up to 250 feet thick. The oldest layer of loess accumulated between 2 and 1 million years ago, while the uppermost layers of Palouse Loess accumulated between 15,000 years ago and modern times. The mid layers of loess were deposited episodically between 77,000 years and 16,000 years ago. During the Pleistocene era the channeled scablands, the northwest portion of MLRA 9, were scoured of topsoil by the Lake Missoula Floods about 15,000-17,000 years ago. Flows removed topsoil from exposed ridges and basalt rims in canyons.

Climate

The climate across MLRA 9 is characterized by moderately cold, wet winters, and relatively dry summers.

Mean Annual Precipitation:
Range: 16 – 28 inches
Winter precipitation, primarily snow, occurs during low-intensity, Pacific-frontal storms. During winter these storms produce occasional rains that fall on frozen or thawing ground surfaces. High intensity, convective thunderstorms produce some rain during the growing season. Precipitation is evenly distributed throughout fall, winter and spring.

Mean Annual Air Temperature:
Range: 40 to 52 F
Freezing temperatures generally occur from late-October through early-April. Temperature extremes are -10 degrees in winter and 110 degrees in summer. Winter fog is variable and often quite localized, as the fog settles on some areas but not others.

Frost-free Period (days):
Total range: 60 to 170
Central tendency: 100 to 140
The growing season for Very Shallow is generally October to mid-November and March through May.

Soil features

Edaphic:

The Very Shallow ecological site commonly occurs with rock outcrop, Shallow Stony or one of the Loamy or North Slope ecological sites. Soils are very shallow to bedrock. Typical soil surface has about 40 percent rock, 10 to 20 percent bare ground, 10 to 20 percent biotic crust and 30 percent vegetative cover. Sites with less than 10 percent vegetative cover can be considered rock outcrop.

Very Shallow sites are sensitive to soil disturbances. When the Very Shallow site is saturated and muddy, physical damage to the site – from vehicle ruts and hoof prints from cows, horses or deer for example – remain intact for many years.

Rocks or plants sitting on pedestals is called pedestaling. Two completely different processes cause the pedestaling. The first process is frost-heaving which pushes the plants upward and is evident across the entire site. The lower part of the soil profile has higher clay content. With winter rain and melting snow, water perches and creates saturated conditions. Freezing weather causes these saturated soils frost-heave, and then during spring thaw, the site becomes muddy. The second pedestaling process is erosion which washes soil away from plants and rocks but only in water flow patterns.

The degree of pedestaling on Very Shallow is quite variable. On many sites the soil surface is smooth and shows little to no evidence of pedestaling. But other sites show a high degree of pedestaling. The difference is presumed to be the amount of clay in the soil and the shrink-swell potential. In some years water runs on the surface and some erosion may occur. If a site has a high degree pedestaling, the observer must determine whether this process is natural or human-induced (water running off cropland onto the rangeland for example).

Representative Soil Features:

This ecological site components are dominantly Lithic taxonomic subgroups of haploxerolls great groups of the Mollisols. Soils are very shallow. Average available water capacity of about 0.6 inches (1.5 cm) in the 0 to 40 inches (0-100 cm) depth range.

Soil parent material is dominantly loess mixed with minor amounts of ash in the upper part of the soil over residuum derived from basalt.

The associated soils are Rockly and similar soils.

Dominate soil surface is very cobbly loam to extremely stony loam.

Dominant particle-size class is loamy-skeletal.

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

Fragments within surface horizon > 3 inches (% Volume):
Minimum: 0
Maximum: 40
Average: 25

Fragments within surface horizon ≤ 3 inches (% Volume):
Minimum: 0
Maximum: 25
Average: 20

Subsurface fragments > 3 inches (% Volume):
Minimum: 10
Maximum: 50
Average: 30

Subsurface fragments ≤ 3 inches (% Volume):
Minimum: 0
Maximum: 25
Average: 20

Drainage Class: Well drained
Water table depth: Greater than 60 inches

Flooding:
Frequency: None

Ponding:
Frequency: None

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

Depth to root-restricting feature (inches):
Minimum: 4
Maximum: 12

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: 0.4
Maximum: 1.0
Average: 0.6

Vegetation dynamics

Ecological Dynamics:

Very Shallow in MLRA 9 produces about 150-300 pounds/acre of biomass annually.
The Very Shallow ecological site in MLRA 9 has four different variations on the short grass theme for the Reference Community. Sandberg bluegrass is dominant in every variation:
1. Stiff sagebrush – Sandberg bluegrass (found only in the Channeled Scabland portion of MLRA 9)
2. Sandberg bluegrass
3. Sandberg bluegrass – one-spike oatgrass
4. Bluebunch wheatgrass – Sandberg bluegrass

In the spring this site has a rich diversity of native annual and perennial forbs on most sites. Very Shallow supports edible species that have been an important food source for the Native Americans for many generations. Bitterroot and biscuitroot are the main species harvested for food.

Sandberg bluegrass is a shallow rooted, perennial bunchgrass, perfectly suited to Very Shallow sites. It has short leaves and a green to purplish panicle seed head. On most sites Sandberg is an understory grass, but on Very Shallow it is the dominant grass. It begins growth in the fall then grows rapidly in the spring and sets seed before moisture is gone. Sandberg bluegrass is resistant to drought, grazing, trampling and fire.

Stiff sagebrush is a short, scraggly-looking and strongly scented with the characteristic sage odor. It is low and spreading with a conspicuously woody base. The base is often heaved from the soil by frost action. The trunk is very irregular, spreading above the base in a dense cluster of short, rigid, and rather brittle branches up to sixteen inches in length. Stiff sagebrush leaves are forked into three deep lobes like fingers. Unlike other sagebrush species, the leaves of stiff sage are deciduous, and by fall, all of the leaves have dropped. The ground under each plant will have a pile of dead leaves.

One-spike oatgrass is a low, densely tufted plant with fuzzy, dull green leaves. The sheath covering the stem has long, dense hairs. At the tip of the stem is one, or occasionally two spikelets.

Impacts of fire and grazing on Very Shallow:
Fire: The vegetative cover is too low to carry fires, so these sites rarely burn
Grazing: In many pastures the Very Shallow sites are not attractive to grazing animals and so are rarely if ever grazed.

Frequent heavy grazing in April & May can be hard on Sandberg bluegrass and the community can become dominated by forbs (native and introduced). To counter this situation, a year of complete rest may be necessary.

Based on inherent protection from both fire and grazing, most Very Shallow sites are stable and in excellent condition. But this is not always the case. In MLRA 8 Very Shallow ridges were hammered by horses or migrating elk.

Many Very Shallow sites in MLRA 9 have ventenata. During wet years Very Shallow can look like a sea of ventenata, but in normal or dry years look like classic Very shallow with only a thin scattering of ventenata.

In many years most grasses remain dormant in the fall. Sandberg bluegrass, however, greens up every year. And so, from late fall through winter and into early spring these Very Shallow sites provide important green forage for deer, elk and upland birds. But these sites also dry up sooner than adjoining sites due to the very shallow soil depth. Grasses are dry from May through September.

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.


Supporting Information:

Associated Sites:
Very Shallow in MLRA 9 is associated with rock outcrop, Shallow Stony, Stony South Slope, Stony Foothills, Loamy bunchgrass, and Loamy dwarf shrub. It is common for Very Shallow sites to transition back and forth with rock outcrop or any of these ecological sites.

Similar Sites:
MLRA 8 Palouse Prairie Very Shallow extends into MLRA 43C Blue Mountains.

Most MLRAs in Eastern Washington has a comparable Very Shallow ecological site:
MLRA 6 East Slope Cascades
MLRA 7 Columbia Basin
MLRA 8 Columbia Plateau

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 009X
Palouse and Nez Perce Prairies

Subclasses

• R009XY301WA–Very Shallow 16-24 PZ

Stage

Provisional

Contributors

K. Guinn, Technical Team: C. Smith, R. Fleenor, K. Paup-Lefferts