Ecological site group R008XG130WA
Loamy, sagebrush
Last updated: 09/21/2023
Accessed: 11/21/2024
Ecological site group description
Key Characteristics
None specified
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): 8 – Columbia Plateau
LRU – Common Resource Areas (CRA):
8.1 - Channeled Scablands
8.2 - Loess Islands
8.3 - Okanogan Drift Hills
8.4 - Moist Pleistocene Lake Basins
8.5 - Moist Yakima Folds
8.7 - Okanogan Valley
Site Concept Narrative:
Note: For MLRA 8 there are four ecological sites with the name ‘Loamy’.
1. One for the sagebrush steppe region
2. One specifically for grasslands on Goldendale Prairie (Klickitat Co.)
3. One specifically for grasslands on south side of Columbia Hills (Klickitat Co.)
4. One for other grassland regions in MLRA 8
a. SE portion of MLRA 8 includes portions of Adams, Franklin, Walla Walla, Asotin, Columbia and Garfield counties
b. Area above Coulee Dam in Douglas Co.
The Loamy ESD below is for the sagebrush steppe areas of MLRA 8 (see 1 above).
Diagnostics:
This upland site occurs in the sagebrush region on 20 inches & deeper non-skeletal loamy soils. Soils have a loamy surface texture and limited rock fragments (generally 10% or less) in the root-growing portions of the soil profile. Silt loam, fine sandy loam and sandy loam are most common, but a variety of soils and landforms are possible.
As one moves across MLRA 8, the landscape position for Loamy changes. At 9 inches of precipitation Loamy occurs on all but the north to northeast slopes. But at 12 inches of precipitation Loamy may be found only on south to southwest slopes. Since Aridic soils in MLRA 8 are 9-12 inches of precipitation, Loamy could be considered an Aridic ecological site.
Fire-sensitive shrubs dominate the reference state overstory, while perennial bunchgrasses and forbs fill the interspaces. The shrub layer is typically waist- to shoulder-high Wyoming sagebrush. The natural fire regime maintains a patchy distribution of shrubs. Depending on the time interval since the last fire, the shrub canopy can be as little 0-3% or as much as 40%. Cool-season bunchgrasses form two distinct layers. Bluebunch wheatgrass is the dominant bunchgrass in the top grass layer, while Sandberg bluegrass is the major grass of the lower grass layer.
Disclaimer Statement:
Loamy, sagebrush ecological site concept covers a variety of soils and site conditions. There are at least four consistent and unifying factors across most of MLRA 8: (1) geology is largely basalt and loess, (2) soils are largely loessal, loess over basalt or loess-influenced, (3) similar climate of moderately cold, wet winters and hot, dry summers, and with limited precipitation, (4) dominant plant species (Wyoming sagebrush and bluebunch wheatgrass for example) that are adapted to a wide variety of soils and site conditions.
With the information and knowledge currently available, the technical team determined that site responses to disturbances, and species composition are similar enough to maintain a single Loamy ecological site across sagebrush steppe areas. If it is later determined that there are significant differences across the variation that must be addressed, this Loamy ecological site will be split into two or more separate ecological sites.
Principle Vegetative Drivers:
The moderately deep to deep silt loam soils drive the vegetative expression of this productive site. Most species have unrestricted rooting on this 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 run off-site or infiltrate into the soil
2. Whether soil condition remain aerobic or become saturated and anaerobic
3. How quickly the soil reaches the wilting point
With adequate cover of live plants and litter, there are no restrictions on Loamy sites with water infiltrating into the soil. These sites are well drained and are saturated for only a short period.
Physiographic Features:
The landscape is part of the Columbia basalt plateau.
Physiographic Division: Intermontane Plateau
Physiographic Province: Columbia Plateau
Physiographic Sections: Walla Walla Plateau Section
Landscapes: Hills, valleys and plateaus
Landform: Sideslopes, terraces, benches, alluvial fans
Elevation: Dominantly 800 to 4,000 feet
Central tendency: 1,000 to 3,000 feet
Slope: Total range: 0 to 90 percent
Central tendency: 2 to 30 percent
Aspect: Occurs on all aspects
Geology:
This MLRA is almost entirely underlain by Miocene basalt flows. Columbia River basalt is covered in many areas with as much as 200 feet of loess and volcanic ash. Small areas of sandstones, siltstones, and conglomerates of the Upper Tertiary Ellensburg Formation are along the western edge of this area. Some Quaternary glacial drift covers the northern edge of the basalt flows, and some Miocene-Pliocene continental sedimentary deposits occur south of the Columbia River, in Oregon.
A wide expanse of scablands in the eastern portion of this MLRA, in Washington, was deeply dissected about 16,000 years ago, when an ice dam that formed ancient glacial Lake Missoula was breached several times, creating catastrophic floods. The geology of the northernmost part of this MLRA is distinctly different from that of the rest of the area. Alluvium, glacial outwash, and glacial drift fill the valley floor of the Okanogan River and the side valleys of tributary streams. The fault parallel with the valley separates pre-Tertiary metamorphic rocks on the west, in the Cascades, from older, pre-Cretaceous metamorphic rocks on the east, in the Northern Rocky Mountains. Mesozoic and Paleozoic sedimentary rocks cover the metamorphic rocks for most of the length of the valley on the west.
Climate
The Wyoming sagebrush-bluebunch wheatgrass areas are both warmer and drier than grasslands or other shrub steppe sites (Daubenmire). The climate is characterized by moderately cold, wet winters, and hot, dry summers, with limited precipitation due to the rain shadow effect of the Cascades. Taxonomic soil climate is either xeric (12 – 16 inches PPT) or aridic moisture regimes (10 – 12 inches PPT) with a mesic temperature regime.
Mean Annual Precipitation:
Range: 10 – 16 inches
Seventy to seventy-five percent of the precipitation comes late October through March as a mixture of rain and snow. June through early October is mostly dry.
Mean Annual Air Temperature:
Range: 44 to 54 F
Central Tendency: 48 – 52 F
Freezing temperatures generally occur from late-October through early-April. Temperature extremes are 0 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: 90 to 210
Central tendency: 120 to 160
The growing season for loamy, sagebrush is March through mid-July.
Soil features
Edaphic:
The Loamy, sagebrush ecological site commonly occurs with Stony, sagebrush, Very Shallow, Cool Loamy and Loamy Bottom ecological sites.
Representative Soil Features:
This ecological site components are dominantly Aridic, Xeric, Calcic and Vitrandic taxonomic subgroups of Haploxerolls, Durixerolls, Palexerolls, Argixerolls and Haploxerepts great groups of the Mollisols and Inceptisols taxonomic orders, with Aridisols occurring as well. Soils are moderately deep to very deep. Average available water capacity of about 5.5 inches (14.0 cm) in the 0 to 40 inches (0-100 cm) depth range.
Soil parent material is dominantly mixed loess with influence of volcanic ash possible.
The associated soils are Alstown, Bagdad, Benwy, Caliralls, Cashmere, Colockum, Dougville, Ellisforde, Manastash, Mikkalo, Newbon, Palerf, Ralock, Renslow and similar soils.
Dominate soil surface is clay loam to very fine sandy loamy, with ashy modifier sometimes occurring as well.
Dominant particle-size class is fine to coarse-silty
Fragments on surface horizon > 3 inches (% Volume):
Minimum: 0
Maximum: 5
Average: 0
Fragments within surface horizon > 3 inches (% Volume):
Minimum: 0
Maximum: 30
Average: 5
Fragments within surface horizon ≤ 3 inches (% Volume):
Minimum: 0
Maximum: 30
Average: 10
Subsurface fragments > 3 inches (% Volume):
Minimum: 0
Maximum: 60
Average: 10
Subsurface fragments ≤ 3 inches (% Volume):
Minimum: 5
Maximum: 50
Average: 15
Drainage Class: Dominantly well drained, but some somewhat excessively drained
Water table depth: Greater than 60 inches
Flooding:
Frequency: None
Ponding:
Frequency: None
Saturated Hydraulic Conductivity Class:
0 to 10 inches: High to moderately low
10 to 40 inches: High to moderately low
Depth to root-restricting feature (inches):
Minimum: 20
Maximum: Greater than 60 inches
Electrical Conductivity (dS/m):
Minimum: 0
Maximum: 10
Sodium Absorption Ratio:
Minimum: 0
Maximum: 10
Calcium Carbonate Equivalent (percent):
Minimum: 0
Maximum: 25
Soil Reaction (pH) (1:1 Water):
0 - 10 inches: 5.1 to 9.6
10 - 40 inches: 5.1 to 9.0
Available Water Capacity (inches, 0 – 40 inches depth):
Minimum: 1.7
Maximum: 9.7
Average: 5.5
Vegetation dynamics
Ecological Dynamics:
Loamy, sagebrush produces about 600-1200 pounds/acre of biomass annually.
Wyoming big sagebrush and bluebunch wheatgrass are at the core of the Loamy ecological site and warrant a degree of understanding.
Wyoming sagebrush in a long-lived, multi-branched, evergreen shrub. Size varies from 3 feet to 5 feet depending on soil and site conditions. Wyoming big sagebrush has a significant rooting system, composed of a two-part rooting structure with a primary deep taproot, and a shallow extensive network of finer roots that spread laterally. This rooting system allows Wyoming big sagebrush to survive in the hottest and driest portions of the sagebrush range by tapping into groundwater sources deep into the soil profile itself. This also allows Wyoming big sagebrush to be more competitive with bunchgrasses when the landscape positions and/or soils are less ideal for grass species to maintain the competitive advantage.
Bluebunch wheatgrass is a long-lived, mid-sized bunchgrass with an awned or awnless seed head arranged is a spike. Bluebunch 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 bluebunch wheatgrass. Refer to page 8 for more details about bluebunch physiology. Research has found that the community remains resistant to medusahead invasion if the site maintains at least 0.8 mid-sized bunchgrass plant/sq. ft. (K. Davies, 2008). It is bluebunch that holds the system together. If we lose the bluebunch the ecosystem crashes or unravels.
The natural disturbance regime for grassland communities is periodic lightning-caused fires. The fire return intervals (FRI) listed in research for sagebrush steppe communities is quite variable. 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 and a range of 50-100 was chosen for Wyoming sagebrush communities (Rapid Assessment Model).
Some fires are spotty or do not burn hot enough to fully remove the sagebrush. Fires with light severity will remove less sagebrush and open smaller patches for grass and forb recovery, whereas the more severe fires will remove almost all the sagebrush and leave vast areas open to return to bunchgrass dominance. This is how the patchy distribution occurs. Rabbitbrush and horsebrush are sprouting shrubs and may also increase following fire.
The effect of fire on the community depends upon the severity of the burn. With a light to moderate fire there can be a mosaic of burned and unburned patches of sagebrush. Sagebrush can return to pre-burn conditions quickly. Bunchgrasses thrive as the fire does not get into the crown. With adequate soil moisture Idaho fescue and bluebunch wheatgrass can make tremendous growth the year after the fire. Other than impacting the sagebrush layer, the community is not affected.
A severe fire puts stress on the entire community. The sagebrush layer is completely removed. Spots or patches with heavy sagebrush are sterilized by the fire and must be seeded to prevent invasive species (annual grasses, tumble mustard) from totally occupying the site. Bluebunch wheatgrass and basin wildrye will have weak vigor for a few years but generally survive. Idaho fescue plants are very much at risk with a severe burn coupled with wind. The result can be “black holes” or ash 2-3 inches into the crown. The death of Idaho fescue plants creates holes in the community, and the opportunity for exotic species to colonize. Needle and thread is one native species that can increase via new seedlings.
For most of MLRA 8, Wyoming sagebrush does not recover easily after fire. The sagebrush in Douglas County, however, returns much more readily. For reasons that have not been clearly established, Douglas County may have a genetically different strain of sagebrush or be enough cooler and wetter, to receive more snowpack to get favorable responses. After disturbances sagebrush often becomes very dense and weedy in nature. Research indicates that microbes in the soil profile are essential for sagebrush success from seed.
The longer the site goes without fire and the more grazing pressure added, the more sagebrush cover increases, and the more bunchgrasses decline. As sagebrush cover increases bluebunch wheatgrass cover declines but individual plants may persist underneath the sagebrush. And, the dense sagebrush community phase is more vulnerable to outside pressures. Invasive species take advantage of available soil rooting spaces. 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 (the same plant grazed more than once). As grazing pressure increases the plant community unravels in stages:
1. Cusick bluegrass, a highly desirable and palatable bunchgrass, declines and is eliminated. Adjacent native species fill the void.
2. Bluebunch wheatgrass declines while Sandberg bluegrass, needle and thread and sagebrush increase
3. As bluebunch wheatgrass continues to decline, invasive species such as cheatgrass and knapweed colonize the site
4. With further decline the site can become a sagebrush-cheatgrass community
Managing sagebrush 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. Bluebunch wheatgrass plants rely principally on tillering, rather than establishment of new plants through natural reseeding. During seed formation, the growing points 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 (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, and (3) to protect the elevated growing points of bluebunch wheatgrass.
Bluebunch wheatgrass remains 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
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, Wyoming sagebrush – bluebunch wheatgrass communities provide habitat for a variety of upland wildlife species.
Supporting Information:
Associated Sites:
Loamy is associated with other ecological sites in the sagebrush steppe areas of MLRA 8, including Shallow Stony, Stony, Cool Loamy, Stony Foothills and Stony Foothills South Slope. It is also associated with Very Shallow, Mound-Intermound Complex, Loamy Bottom, Alkali Terrace, Sodic Flat, and Riparian Complex.
Similar Sites:
Loamy sagebrush in MLRA 8 Columbia Plateau is a bluebunch wheatgrass – Wyoming sagebrush ecological site. Loamy in MLRA 7 Columbia Basin is also a similar shrub steppe site.
In MLRA 8 the other Loamy ecological sites – Loamy Goldendale Prairie, Loamy grassland and Loamy South Aspect Columbia Hills do not have sagebrush.
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 008X
Columbia Plateau
Subclasses
Stage
Provisional
Contributors
Technical Team: K. Moseley, G. Fults, R. Fleenor, W. Keller, C. Smith, K. Bomberger, C. Gaines, K. Paup-Lefferts
Provisional Site Author: Kevin Guinn
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