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
 
Site Concept Narrative:
Diagnostics:

The channeled scabland-loess island region is the only portion of MLRA 9 that is shrub steppe. Stony foothills, channeled scabland occurs on two Common Resource Areas – 9.1 channeled scabland and 9.12 loess islands. This site is also found in Daubenmire’s Threetip Sagebrush-Fescue vegetative zone.

Fire sensitive, bitterbrush dominates the reference state overstory, while perennial bunchgrasses such as Idaho fescue and bluebunch wheatgrass are dominant in the herbaceous understory. The shrub layer is typically waist- to shoulder-height bitterbrush with a mix of other shrub steppe species scattered throughout including Wyoming sagebrush, rabbitbrush, and currant.

Stony foothills, channeled scabland is an upland bitterbrush-bunchgrass site occurring in the transition between threetip sagebrush and forest in eastern Lincoln, southwestern Spokane, and northwestern Whitman counties. The soils are deep (60 inches or greater), coarse textured and rocky. Textures are mostly sandy loam and sand with some loams. Soils are often gravelly to very gravely to extremely stony. Soils are well drained.

Principle Vegetative Drivers:

The coarse soils and neutral to north aspect drive the vegetative expression of this site. Bitterbrush prefers well drained, coarse soils, while the neutral or north slopes are good for both bluebunch and Idaho fescue.

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

With adequate plant cover and litter, the water infiltrates into Stony Foothills readily. These sites are well drained and are saturated for only a short period.

Physiographic Features:

The landscape is part of the Columbia basalt plateaus and Northern Rocky foothills. 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.

MLRA 9 has three distinct geographical areas:
(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

Landscapes: plateaus and loess hills
Landform: Dominantly benches, terraces, terraces escarpments

Elevation: Dominantly 1,800 to 3,000 feet
Slope: Total range: 0 to 60 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.

The Channeled Scabland was impacted by the Missoula Floods, but the Loess Islands were not inundated or scoured by the floodwaters.

Climate

The channeled scabland region is the coldest and driest part of MLRA 9. The climate across MLRA 9 is characterized by moderately cold, wet winters, and relatively dry summers.

Mean Annual Precipitation:
Range: 14 – 18 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: 42 to 52 F
Central Tendency: 47 to 50 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.

Areas with threetip sagebrush and Idaho fescue when compared to Wyoming sagebrush-bluebunch wheatgrass regions, are cooler from late fall to early spring (October through April), and has higher P (precipitation) and P/T (precipitation-transpiration) for five months (September, November, December, January and March) (Daubenmire).

Frost-free period (days):
Total range: 60 to 180
Central tendency: 100 to 140
The growing season for Stony foothills is April through end of July.

Soil features

Edaphic:

The Stony foothills, channeled scabland ecological site occurs with Cool loamy, channeled scabland and Ponderosa pine ecological sites.

Representative Soil Features:

This ecological site components are dominantly Vitrandic and Lithic taxonomic subgroups of Argixerolls and Haploxerolls taxonomic great group of the Mollisols taxonomic order. Soils are dominantly very deep. Average available water capacity of about 2 inches (5.1 cm) in the 0 to 40 inches (0-100 cm) depth range.

Soil parent material is dominantly glaciofluvial deposits with loess and volcanic as in the upper part, residuum and colluvium.

The associated soils are Alecanyon, Cheney and similar soils.

Dominate soil surface is silt loam to gravelly ashy coarse sandy loam.

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

Fragments within surface horizon > 3 inches (% Volume):
Minimum: 5
Maximum: 20
Average: 15

Fragments within surface horizon ≤ 3 inches (% Volume):
Minimum: 5
Maximum: 20
Average: 10

Subsurface fragments > 3 inches (% Volume):
Minimum: 10
Maximum: 30
Average: 20

Subsurface fragments ≤ 3 inches (% Volume):
Minimum: 10
Maximum: 40
Average: 30

Drainage Class: Excessively and well drained
Water table depth: Dominantly greater than 60 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 and high

Depth to root-restricting feature (inches):
Minimum: Dominantly greater than 60, but strongly contrasting textural stratification can occur up to 20 inches occurrences
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 7.8
10 - 40 inches: 6.1 to 7.8

Available Water Capacity (inches, 0 – 40 inches depth):
Minimum: 3.5
Maximum: 9.3
Average: 7

Vegetation dynamics

Ecological Dynamics:

Stony foothills, channeled scabland produces about 1100-1600 pounds/acre of biomass annually.

Antelope bitterbrush, Idaho fescue and bluebunch wheatgrass are at the core of the Stony Foothills ecological site and warrant a degree of understanding. Antelope bitterbrush is a very palatable, high quality shrub for big game and livestock. It is adapted to a wide range of soils and precipitation. Bitterbrush is usually 2-6 feet in height and up to 8 feet in width. Rodents normally cache bitterbrush seed within 50-75 feet of an existing seed source. Following a fire, the rodent seed caches become an important source of regeneration. Another important source of regeneration are pockets of unburned rangeland that provide much needed seed to the system.

Idaho fescue is shorter and has a dense clump of shoots, while bluebunch wheatgrass is taller and is less dense. Both species are long-lived bunchgrasses. Bluebunch has an awned or awnless inflorescence arranged in a spike while Idaho fescue has an awned inflorescence arranged in a panicle. The ratio of Idaho fescue to bluebunch wheatgrass plants on any site can vary due to aspect and elevation.

Needle-and-thread is another perennial bunchgrass on Stony Foothills. It produces erect, unbranched stems about 3 feet in height. The sharp-pointed seeds have a 4 to 5-inch long twisted awn. With wetting and drying needle and thread seed drills itself into the ground. Thus, needle and thread is one of the best seeders in the reference plant community. With grazing pressure on the dominant bunchgrasses, needle-and-thread increases.

In healthy communities, these mid-sized grasses provide 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. This root-network stabilizes the soils, provides organic matter and nutrients, and helps to maintain soil pore space for water infiltration and retention un the soil profile. The extensive rooting system of mid-sized grasses leave very little space for invasion by other species. This drought resistant root mass 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 and bluebunch wheatgrass. Research has found that on similar rangeland the community remains resistant to medusahead if the site maintains at least 0.8 mid-sized bunchgrass plant/sq. ft. (Davies). These two bunchgrasses hold 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. How one answers fire return intervals for bitterbrush communities depends on the frame of reference used. Current conditions for Stony Foothills are communities often dominated by dense canopies of bitterbrush, some of which has become decadent. These shrubs are 50-100 years old or older due to fire suppression. These bitterbrush plants do not readily re-sprout following fire. Germinating seeds, especially from rodent caches is the primary source to bitterbrush re-establishment. The framework of current conditions suggests a fire return interval of 50-100 years or longer.

Miller et al, paint a totally different picture for pre-settlement mountain big sage-bitterbrush-fescue communities. These communities were dominated by the herb layer. Shrubs were widely scattered and patchy. The fire regime was high frequency (10-20 years), low severity, low intensity. The landscape would have been a mosaic of burned and unburned patches. In any given fire some bitterbrush plants would have survived the fire. Also, bitterbrush plants were likely much younger (10-30 years old), more vigorous and more likely to sprout following fire. In recent years sprouting bitterbrush after low severity fire supports the notion of sprouting bitterbrush. Seedlings from rodent caches would have also been important for the recovery of the shrub layer.

The effect of fire on the main species is mixed for the Stony Foothills site. Bitterbrush is very susceptible to fire kill and is considered a weak sprouter. Bluebunch wheatgrass and needle and thread are fire tolerant, but Idaho fescue is much more sensitive to fire. Under windy conditions, a fire can burn into the crown of Idaho fescue, leaving behind “black holes” or nothing but ash. When a site loses its Idaho fescue, the holes will be filled by vigorous native species or exotic weeds. Bluebunch wheatgrass keeps the site resistant to change, while bitterbrush and Idaho fescue makes the site more at risk.

A low intensity, high frequency fire regime favors bitterbrush sprouting and rapid tillering by both Idaho fescue and bluebunch wheatgrass. A high intensity, low frequency fire regime hinders recovery – Idaho fescue plants may be devastated, bluebunch wheatgrass set back, and bitterbrush regeneration limited to seedlings.

Fires with light severity will remove less bitterbrush and open smaller patches for grass and forb recovery, whereas the more severe fires will remove almost all the bitterbrush and leave vast areas open to return to bunchgrass dominance. This is how the patchy distribution occurs. So, fire resets the competitive advantage back to the bunchgrasses by removing much of the overstory. This, in turn, maintains the stability and overall resilience of the site. However, this is not always true as some fires are spotty or do not burn hot enough to fully remove the bitterbrush. Rabbitbrush and horsebrush are sprouting shrubs and may also increase following fire.

The longer the site goes without fire and the more grazing pressure added to the bunchgrasses, the more bitterbrush cover increases, and the more bunchgrasses decline. This leaves the dense bitterbrush community phase more vulnerable to outside pressures. Invasive species take advantage of the available soil rooting spaces in the interspaces. The once extensive grass roots are largely absent. Soils are no longer receiving the organic inputs, and there is less surface cover by grass litter. Both water infiltration into the soil, and water percolation through the soil, are affected, leaving open soil space that is drier and more vulnerable to wind and water erosion, and invasion by undesirable species. Once these undesirable species have colonized, the site is at high risk of crossing a threshold if a disturbance such as fire were to occur.

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 (same plants grazed more than once). As grazing pressure increases the plant community unravels in stages:
1. Cusick bluegrass is eliminated. Adjacent natives fill the void
2. Idaho fescue declines while bluebunch wheatgrass and threetip sagebrush increase
3. Both Idaho fescue and bluebunch wheatgrass decline while threetip sage and threadleaf sedge increase
4. With further decline invasive species colonize the site
5. The site can become a shrub-annual grass community

Managing shrub steppe 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.

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 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.

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

Antelope bitterbrush is an important browse species for big game animals and needs special management consideration with livestock in mind. There is no problem with spring grazing as livestock do not focus their attention to bitterbrush in the spring. Fall is a different story. Feeding some alfalfa every second or third day helps minimize livestock use of bitterbrush in the fall.

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, antelope bitterbrush / Idaho fescue /bluebunch wheatgrass communities provide habitat for big game and sharp-tailed grouse.

Supporting Information:
 
Associated Sites:
Stony Foothills, channeled scabland is associated with Cool Loamy and ponderosa pine forest sites.

Similar Sites:
MLRA 6 East Slope of the Cascades and MLRA 8 Columbia Plateau have comparable Stony Foothills ecological sites.

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

Stage

Provisional

Contributors

Kevin Guinn, R. Fleenor, K. Paup-Lefferts, W. Keller