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Ecological site R008XY978WA

Sodic Flat

Last updated: 5/23/2025
Accessed: 10/18/2025

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General information

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.

MLRA notes

Major Land Resource Area (MLRA): 008X–Columbia Plateau

MLRA 8 encompasses about 50,100 square kilometers mainly in Washington and Oregon, with a small area in Idaho. This MLRA is characterized by loess hills, surrounding scablands, and alluvial deposits. This MLRA consists mostly of Miocene Columbia River Basalt covered with up to 200 feet of loess and volcanic ash. The dominant soil order in this MLRA is Mollisols. Soils in this MLRA dominantly have a mesic temperature regime, a xeric moisture regime, and mixed minerology.

Classification relationships

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
8.6 - Lower Snake and Clearwater Canyons
8.7 - Okanogan Valley

Ecological site concept

In the upland setting ecological sites are often expansive, and thus, can be delineated and separated on aerial photos. But in the landscape position of bottoms, basins and depressions this is rarely the case as small changes in soil chemistry, the water table and elevation or aspect results in significant changes in plant community composition. In short distances there are often big swings of available water holding capacity, and soils can go from hydric to non-hydric, or from saline-sodic to not. So, in bottoms, riparian areas and depressions, ecological sites and community phases occur as small spots, strips and patches, or as narrow rings around vernal ponds. And generally, in a matter of steps one can walk across several ecological sites. On any given site location, two or more of these sites occur as a patchwork – Loamy Bottom, Alkali Terrace, Sodic Flat, Wet Meadow, Herbaceous Wetland and Riparian Woodland. These ecological sites may need to be mapped as a complex when doing resource inventory.

Diagnostics:

Sodic Flat has a two-layered plant community. The top layer is scattered or patchy black greasewood, which is a three to six feet tall deciduous shrub with spines and fleshy leaves. The bottom layer, saltgrass, is a short, warm season rhizomatous grass. At the soil surface Sodic Flat is a patchy network of bare ground and saltgrass as there is no moss or lichens.

Sodic Flat is part of the lentic (standing water) ecosystem. It occurs on valley flats, bottoms, basins, terraces and depressions. This site may also occur as a narrow zonal ring around ponds and vernal pools. Soils are typically deep, clay loam and silt loam texture and have limited rock fragments (generally 10 percent or less) in the root-growing portions of the soil profile. Soils are hydric and strongly to very strongly alkaline.

Sodic Flat is a harsh site. Not many plant species can tolerate the sodic conditions.

Principle Vegetative Drivers:

An elevated water table and very strongly alkaline-sodic soil chemistry drive the vegetative expression of the Sodic Flat ecological site. A limited number of plant species are adapted to the high pH. Conditions are so harsh that 40-80% of the soil surface is bare. Saltgrass is spotty and greasewood is scattered or patchy across the site.

Associated Sites:
Sodic Flat is associated with other ecological sites in bottoms and basin areas of MLRA 8, including Alkali Terrace, Loamy Bottom, Wet Meadow, Wetland Complex and Riparian Complex. Alkali Terrace is also associated with upland sites such as Loamy, Stony, Very Shallow and Cool Loamy.

Similar Sites:
MLRA 7 Columbia Basin has a comparable Sodic Flat ecological site.

Associated sites

R008XY970WA	Alkali Terrace
R008XY980WA	Wet Meadow
R008XY930WA	Loamy Bottom

R008XY970WA

Alkali Terrace

R008XY980WA

Wet Meadow

R008XY930WA

Loamy Bottom

Similar sites

R007XY978WA	Sodic Flat

R007XY978WA

Sodic Flat

Table 1. Dominant plant species

Tree	Not specified
Shrub	(1) Sarcobatus vermiculatus
Herbaceous	(1) Distichlis spicata

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Physiographic features

The landscape is part of the Columbia basalt plateau. Sodic Flat occurs on valley flats, bottoms, basins, terraces and depressions. This site may also occur as a narrow zonal ring around ponds and vernal pools. So, in bottoms, riparian areas and depressions, ecological sites and community phases occur as small spots, strips and patches, or as narrow rings around vernal ponds. Generally, in a matter of steps one can walk across several ecological sites. On any given site location, two or more of these sites occur as a patchwork of Loamy Bottom, Alkali Terrace, Sodic Flat, Wet Meadow, Herbaceous Wetland, and Riparian Complex. These ecological sites may need to be mapped as a complex when doing resource inventory.

Physiographic Division: Intermontane Plateau
Physiographic Province: Columbia Plateau
Physiographic Sections: Walla Walla Plateau Section

Landscapes: Hills and plateaus
Landform: Drainageways, depressions and terraces

Table 2. Representative physiographic features

Landforms	(1) Hills (2) Plateau (3) Drainageway (4) Depression (5) Terrace
Flooding frequency	None to rare
Ponding frequency	Frequent
Elevation	1,000 – 3,600 ft
Slope	5%
Water table depth	60 in
Aspect	W, NW, N, NE, E, SE, S, SW

Table 3. Representative physiographic features (actual ranges)

Flooding frequency	Not specified
Ponding frequency	Not specified
Elevation	Not specified
Slope	15%
Water table depth	Not specified

Climatic features

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 to 16 inches of precipitation) or aridic moisture regimes (10 to 12 inches of precipitation) with a mesic temperature regime.

Table 4. Representative climatic features

Frost-free period (characteristic range)	110-160 days
Freeze-free period (characteristic range)
Precipitation total (characteristic range)	10-16 in
Frost-free period (actual range)	90-200 days
Freeze-free period (actual range)
Precipitation total (actual range)

Influencing water features

Sodic Flat soils are poorly drained to moderately well drained and have mostly slow permeability. So, there are significant restrictions with water infiltrating into the soil, and thus, the soils remain saturated and in an anaerobic condition from late winter to mid-spring. By late summer Sodic Flat is dry.

Soil features

This ecological site components are dominantly Typic and Duric taxonomic subgroups of Halaquepts and Natrixerolls great groups of the Mollisols and Inceptisols taxonomic order. Soils are moderately deep to very deep. Average available water capacity of about 5.5 inches (14.0 cm) in the zero to 40 inches (zero to 100 cm) depth range.

Soil parent material is dominantly mixed alluvium.

The associated soils are Emdent, Halaquepts, Spofford, Umapine, Weissenfels and similar soils.

Dominate soil surface is silt loam to very fine sandy loam, with ashy modifier sometimes occurring as well.

Dominant particle-size class is fine to coarse-loamy.

Table 5. Representative soil features

Parent material	(1) Alluvium
Surface texture	(1) Silt loam (2) Very fine sandy loam
Family particle size	(1) Fine (2) Coarse-loamy
Depth to restrictive layer	20 – 60 in
Soil depth	60 in
Surface fragment cover <=3"	2%
Surface fragment cover >3"	1%
Available water capacity (0-40in)	5.5 in
Calcium carbonate equivalent (Depth not specified)	20%
Electrical conductivity (Depth not specified)	10 mmhos/cm
Sodium adsorption ratio (Depth not specified)	15 – 30
Soil reaction (1:1 water) (0-10in)	6.6 – 11
Subsurface fragment volume <=3" (Depth not specified)	5%
Subsurface fragment volume >3" (Depth not specified)	4%

Table 6. Representative soil features (actual values)

Depth to restrictive layer	Not specified
Soil depth	Not specified
Surface fragment cover <=3"	5%
Surface fragment cover >3"	5%
Available water capacity (0-40in)	4 – 8.3 in
Calcium carbonate equivalent (Depth not specified)	Not specified
Electrical conductivity (Depth not specified)	Not specified
Sodium adsorption ratio (Depth not specified)	Not specified
Soil reaction (1:1 water) (0-10in)	Not specified
Subsurface fragment volume <=3" (Depth not specified)	15%
Subsurface fragment volume >3" (Depth not specified)	10%

Ecological dynamics

Sodic Flat produces about 1,500 pounds per acre of biomass annually.

Regarding saline-alkali soils Daubenmire (page 50) wrote, “It seems impossible to find areas where one can be confident that the vegetation has not been somewhat altered by domesticated animals.” Some areas were also manipulated by tillage or other farming practices.

Black greasewood is a spiny, deciduous, semi-evergreen shrub that grows three to 10 feet tall. It has high tolerance to sodic and saline affected soils. Greasewood is highly drought tolerant but can also tolerate a high, water table.

Generally, greasewood receives limited grazing from livestock. Greasewood plants contain sodium and potassium oxalates, and are toxic to livestock, but can be safely grazed in light amounts in the spring while the leaves ae growing. This shrub sprouts readily following a fire. Greasewood can tap into groundwater at a great depth.

Greasewood and saltgrass have greater tolerance of high salinity, high water table and pH than does basin wildrye. So, basin wildrye has limited adaptation to Sodic Flat.

Saltgrass is a short, warm-season, sod-forming grass that can form dense mats with rhizomes and sometimes stolons. Saltgrass is one of the most common plants found on saline-alkaline soils and it is one of the most drought tolerant species. Being rhizomatous, saltgrass is tolerant of moderate to heavy grazing, and as a warm-season grass, it provides green forage a little longer than adjacent upland sites.

Among plants there is a decreasing tolerance of high-water table and high salinity:
Winterfat, spiny hopsage, rabbitbrush, big sagebrush, saltgrass, alkaligrass, spike-rush, basin wildrye, and western wheatgrass

Fire and grazing are two of the main disturbances to the rangeland of Eastern Washington. Fire has minimal effect on Sodic Flat sites. Saltgrass is rhizomatous with growing points protected below ground, while greasewood readily sprouts when burned. Under heavy grazing pressure the amount of bare ground will increase and over time invasive species colonize.

In Washington, greasewood and saltgrass communities provide habitat for a variety of upland wildlife species.

State and transition model

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State 1
Reference Sagebrush Steppe with No Invasive Species

State 1 represents Sodic Flat with no invasive or exotic species. All the functional, structural groups have one or more species. Reference State Community Phases: 1.1 Reference Black greasewood – Saltgrass 1.2 Shrub Black Greasewood 1.3 Bunchgrass – Rhizomatous Grass Foxtail barley – Saltgrass Dominate Reference State Species: Black greasewood, saltgrass At-risk Communities: • All communities in the reference state are at risk of invasive species. Annual or biennial weeds and annual grass seeds blow onto most sites annually • Community 1.3 is most at risk of invasion

Community 1.1
Reference Black Greasewood, Saltgrass, and other Native Grasses

40% black greasewood 40% saltgrass 15% other native grasses

Figure 1. Annual production by plant type (representative values) or group (midpoint values)

Community 1.2
Deciduous Shrub Community Black Greasewood and Saltgrass

70% black greasewood 20% saltgrass 5% other grasses

Community 1.3
Weedy Bunchgrasses and Rhizomatous Grasses

Foxtail barley and saltgrass

Pathway 1.1A
Community 1.1 to 1.2

Result: Shift from Reference Community 1.1 (shrub-rhizomatous grass) to Community 1.2 (deciduous shrub dominated community). Greasewood increases as saltgrass declines. Primary Trigger: heavy to severe grazing (heavy grazing intensity or an extended grazing period) Ecological process: with consistent defoliation pressure saltgrass has poor vigor, fewer shoots and shorter shoots. As saltgrass cover declines greasewood increases via new seedlings. Rabbitbrush may also increase. Indicators: declining saltgrass cover, increasing greasewood (number of plants and cover).

Pathway 1.2A
Community 1.2 to 1.3

Result: shift from Community 1.2 (deciduous shrub) to Community 1.3 (weedy bunchgrass-rhizomatous grass). Primary Trigger: Moderate-severity to high-severity fire. Secondary trigger would be a mechanical shrub control treatment. Ecological Process: fire or mowing kills the greasewood. This releases resources and niche space. Foxtail barley is a pioneer species following disturbances, and seedlings establish quickly. Indicators: greatly diminished greasewood cover, increased cover of foxtail barley.

State 2
Invasive Species

State 2 represents Sodic Flat where invasive broadleaf weeds and/or invasive annual grasses have prominence. Foxtail barley is present and saltgrass has been reduced.to scattered patches Community Phases for State 2: State 2 can have several variations: 1. Invasive broadleaf weeds with foxtail barley and saltgrass patches 2. Invasive annual grasses with foxtail barley and saltgrass patches 3. Both variations above can be with or without some greasewood and/or rabbitbrush Some Invasive Species in State 2: cheatgrass perennial pepperweed rabbitsfoot grass alkali grass

Community 2.1
Invasive Species

Invasive broadleaf weeds, foxtail barley, saltgrass, and invasive annual grasses. Greasewood may be present.

Transition T1A
State 1 to 2

Result: shift from Reference state with no invasive species to State 2 with invasive species Primary Trigger: heavy to severe grazing pressure (heavy to severe grazing intensity or extended grazing period). Ecological process. With consistent defoliation saltgrass has reduced vigor and bare ground increases which provide opportunities for invasive species to colonize and expand. Weed seeds blow onto most sites annually. Indicators: initially reduced cover of saltgrass and increasing bare ground. The presence of invasive species where none has occurred. Later increasing cover of invasive species. Recovery State 2 is considered non-reversible. Sodic Flat is a harsh site. Soils are very strongly alkaline and sodic. Seeding success would be very problematic. Seeding is not a viable option economically or from a plant adaptability standpoint.

Additional community tables

Table 7. Community 1.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production (lb/acre)	Foliar cover (%)
Shrub/Vine
1	Dominant Sprouting Shrub			600–
	greasewood	SAVE4	Sarcobatus vermiculatus	–	–
2	Other Sprouting Shrubs - Trace			0–
	rabbitbrush	CHRYS9	Chrysothamnus	–	–
Grass/Grasslike
3	Other Native Grasses - Minor			300–
	basin wildrye	LECI4	Leymus cinereus	–	–
	foxtail barley	HOJU	Hordeum jubatum	–	–
	Sandberg bluegrass	POSE	Poa secunda	–	–
	alkali cordgrass	SPGR	Spartina gracilis	–	–
4	Dominant Rhizomatous Warm-Season Grass			600–
	saltgrass	DISP	Distichlis spicata	–	–
5	Other Graminoids - Minor			45–
	arctic rush	JUAR2	Juncus arcticus	–	–
Forb
6	Native Forbs - Minor			30–
	common yarrow	ACMI2	Achillea millefolium	–	–

Supporting information

Other references

Boling M., Frazier B., Busacca, A., General Soil Map of Washington, Washington State University, 1998 Daubenmire, R., Steppe Vegetation of Washington, EB1446, March 1968

Davies, Kirk, Medusahead Dispersal and Establishment in Sagebrush Steppe Plant Communities, Rangeland Ecology & Management, 2008 Environmental Protection Agency, map of Level III and IV Ecoregions of Washington, June 2010

Miller, Baisan, Rose and Pacioretty, “Pre and Post Settlement Fire regimes in mountain Sagebrush communities: The Northern Intermountain Region Natural Resources Conservation Service, map of Common Resource Areas of Washington, 2003 Rapid Assessment Reference Condition Model for Wyoming sagebrush, LANDFIRE project, 2008

Rocchio, Joseph & Crawford, Rex C., Ecological Systems of Washington State. A Guide to Identification. Washington State Department of Natural Resources, October 2015. Pages 156-161 Inter-Mountain Basin Big Sagebrush

Rouse, Gerald, MLRA 8 Ecological Sites as referenced from Natural Resources Conservation Service-Washington FOTG, 2004 Soil Conservation Service, Range Sites for MLRA 8 from 1980s and 1990s

Tart, D., Kelley, P., and Schlafly, P., Rangeland Vegetation of the Yakima Indian reservation, August 1987, YIN Soil and Vegetation Survey

Contributors

Kevin Guinn

Approval

Kirt Walstad, 5/23/2025

Acknowledgments

Provisional Site Author: Kevin Guinn

Technical Team: K. Moseley, G. Fults, R. Fleenor, W. Keller, C. Smith, K. Bomberger, C. Gaines, K. Paup-Lefferts

Rangeland health reference sheet

Interpreting Indicators of Rangeland Health is a qualitative assessment protocol used to determine ecosystem condition based on benchmark characteristics described in the Reference Sheet. A suite of 17 (or more) indicators are typically considered in an assessment. The ecological site(s) representative of an assessment location must be known prior to applying the protocol and must be verified based on soils and climate. Current plant community cannot be used to identify the ecological site.

Author(s)/participant(s)
Contact for lead author
Date	05/13/2025
Approved by	Kirt Walstad
Approval date
Composition (Indicators 10 and 12) based on	Annual Production

Indicators

Number and extent of rills:
Presence of water flow patterns:
Number and height of erosional pedestals or terracettes:
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
Number of gullies and erosion associated with gullies:
Extent of wind scoured, blowouts and/or depositional areas:
Amount of litter movement (describe size and distance expected to travel):
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
Functional/Structural Groups (list in order of descending dominance by above-ground annual-production or live foliar cover using symbols: >>, >, = to indicate much greater than, greater than, and equal to):

Dominant:

Sub-dominant:

Other:

Additional:
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
Average percent litter cover (%) and depth ( in):
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
Potential invasive (including noxious) species (native and non-native). List species which BOTH characterize degraded states and have the potential to become a dominant or co-dominant species on the ecological site if their future establishment and growth is not actively controlled by management interventions. Species that become dominant for only one to several years (e.g., short-term response to drought or wildfire) are not invasive plants. Note that unlike other indicators, we are describing what is NOT expected in the reference state for the ecological site:
Perennial plant reproductive capability:

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