Natural Resources
Conservation Service

Ecological site R008XY970WA

Alkali Terrace

Last updated: 5/23/2025
Accessed: 07/14/2026

Home / esd CATALOG / MLRA 008X / ecological site R008XY970WA

USC

Metric

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:

Alkali Terrace is a grassland site featuring a dichotomy of two grasses. Scattered across a carpet of short warm-season sod-forming grass, are tall cool-season bunchgrasses. The overstory is tall, upright basin wildrye (Leymus cinereus) while the much shorter saltgrass (Distichlis sp.) fills the interspaces.

Alkali Terrace is part of the lentic (standing water) ecosystem. It occurs on moisture receiving sites such as terraces, bottoms, basins, fans and depressions. This site also occurs as a narrow zonal ring around ponds, lakes and vernal pools.

Soils are typically deep, ashy loam or clay loam texture and mostly have little rock fragments. Soils are moderately alkaline but not hydric. The sols are moderately saline-sodic and conspicuously bare between the vascular plants as there is no moss or lichen.

Occasionally one will find a subset of Alkali Terrace – saltgrass with no basin wildrye or shrubs. This version of Alkali Terrace has much smaller acreage and much lower production than the more prevalent sites with basin wildrye and saltgrass.

Principle Vegetative Drivers:

Moderately saline-sodic soil conditions and deep soils drive the vegetative expression of the Alkali Terrace ecological site. Basin wildrye and saltgrass are both at home on this site. Winter & spring – water table at 30 to 40 inches.

Associated Sites:
Alkali Terrace is associated with bottomland sites – Loamy Bottom, Sodic Flat, Wet Meadow, Wetland Complex and Riparian Complex ecological sites. It is also associated with upland sites such as Loamy Cool, Loamy, and Stony.

Similar Sites:
MLRA 7 Columbia Basin has a comparable Alkali Terrace ecological site.

Associated sites

R008XY402WA	Loamy Bottom 10-16 PZ
R008XY978WA	Sodic Flat
R008XY720WA	Riparian Complex
R008XY435WA	Loamy 14-20 PZ Goldendale Prairie
R008XY455WA	Loamy North Aspect 14-20 PZ Goldendale Prairie

Similar sites

R007XY970WA	Alkali Terrace

R007XY970WA

Alkali Terrace

Table 1. Dominant plant species

Tree	Not specified
Shrub	(1) Sarcobatus vermiculatus
Herbaceous	(1) Leymus cinereus (2) Distichlis

Download full description

Physiographic features

The landscape is part of the Columbia basalt plateau. Alkali Terrace occurs on moisture receiving sites such as terraces, bottoms, basins, fans and depressions and this site also occurs as a narrow zonal ring around ponds, lakes 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 – 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, valleys and plateaus
Landform: Floodplains, terraces, drainageways and depressions

Table 2. Representative physiographic features

Landforms	(1) Hills (2) Valley (3) Plateau (4) Flood plain (5) Terrace (6) Drainageway (7) Depression
Flooding frequency	None to occasional
Ponding frequency	None to frequent
Elevation	500 – 2600 ft
Slope	0 – 5 %
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	0 ft
Slope	0 – 15 %

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 PPT) or aridic moisture regimes (10 to 12 inches PPT) 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)	10-20 in
Frost-free period (actual range)	90-200 days
Freeze-free period (actual range)
Precipitation total (actual range)

Influencing water features

Alkali Terrace receives both surface runoff and discharging groundwater from nearby upland sites. The soils are deep and very deep, somewhat poorly to well drained and unrestricted, and thus, remain saturated for only a short period in late winter to early spring. With adequate cover of live plants and litter, there are no water infiltrating restrictions on Alkali Terrace.

Soil features

This ecological site components are dominantly Typic, Xeric and Pachic taxonomic subgroups of Haploxerolls, Palexerolls and Haplodurids great groups of the Mollisols and Aridisols taxonomic order, with Inceptisols occurring as well. Soils are dominantly deep or very deep but limited moderately deep occurs as well. Average available water capacity of about five inches (12.7 cm) in the zero to 40 inches (zero to 100 cm) depth range.

Soil parent material is dominantly mixed alluvium.

The associated soils are Aquolls, Emdent, Gooseflats, Leahy, Mitta, Nack, Pedigo, Stanfield and similar soils.

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

Dominant particle-size class is fine to loamy-skeletal

Table 5. Representative soil features

Parent material	(1) Alluvium
Surface texture	(1) Silt loam (2) Gravelly loam
Family particle size	(1) Fine (2) Loamy-skeletal
Drainage class	Somewhat poorly drained to well drained
Depth to restrictive layer	40 – 60 in
Soil depth	60 – 0 in
Surface fragment cover <=3"	0 – 5 %
Surface fragment cover >3"	0 – 1 %
Available water capacity (0-40in)	0 – 5 in
Calcium carbonate equivalent (Depth not specified)	5 – 30 %
Electrical conductivity (Depth not specified)	0 – 30 mmhos/cm
Sodium adsorption ratio (Depth not specified)	0 – 30
Soil reaction (1:1 water) (0-10in)	5.6 – 11
Subsurface fragment volume <=3" (Depth not specified)	0 – 10 %
Subsurface fragment volume >3" (Depth not specified)	0 – 5 %

Table 6. Representative soil features (actual values)

Drainage class	Not specified
Depth to restrictive layer	0 in
Soil depth	0 in
Surface fragment cover <=3"	0 – 20 %
Surface fragment cover >3"	0 – 5 %
Available water capacity (0-40in)	1.4 – 8.3 in
Calcium carbonate equivalent (Depth not specified)	0 %
Electrical conductivity (Depth not specified)	0 mmhos/cm
Sodium adsorption ratio (Depth not specified)	0
Soil reaction (1:1 water) (0-10in)	0
Subsurface fragment volume <=3" (Depth not specified)	0 – 45 %
Subsurface fragment volume >3" (Depth not specified)	0 – 15 %

Ecological dynamics

Alkali Terrace produces about 3,000 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.

Basin wildrye, also called Great Basin wildrye, and inland saltgrass are at the core of the Alkali Terrace ecological site and warrant a degree of understanding. Basin wildrye is a tall, cool-season bunchgrass and has coarse, robust stems and leaves. It grows five to seven feet tall and sometimes exceeds three feet in diameter and, is one of the highest producing species. Basin wildrye is commonly found on loamy bottoms, saline-alkali soils and on the tops of loamy mounds. It tolerates alkaline soils and seasonal flooding but not anaerobic conditions. Basin wildrye is considered weakly rhizomatous.

Saltgrass is a short, warm-season, sod-forming grass that can form dense mats with its rhizomes and sometimes stolons. Saltgrass is one of the most common plants found on saline-alkaline soils. It is one of the most drought tolerant species. Being rhizomatous, saltgrass is tolerant of moderate to heavy grazing.

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 to 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 to 100 was chosen for Wyoming sagebrush communities (Rapid Assessment Model).

Because basin wildrye produces a large amount of biomass, fire can burn and smolder in the crown of the plant for considerable time. This can leave basin wildrye plants much diminished. It can take years for basin wildrye to fully recover from the effects of fire. Saltgrass, being rhizomatous, is quite tolerant of fire, but due to limited fuel, often does not burn.

Grazing is another common disturbance that occurs in this ecological site. Grazing pressure can be defined as heavy grazing intensity, or frequent grazing during reproductive growth, or season-long grazing. As grazing pressure increases the plant community unravels in stages:
1. Basin wildrye plants produce fewer shoots and tillers and become smaller allowing saltgrass to expand
2. As the decline continues invasive species such as perennial pepperweed and cheatgrass colonize the site
3. With further decline the site can become an invasive weed community

Saltgrass is quite tolerant of grazing, and as a warm-season grass it provides green forage a little longer than adjacent upland sites. Basin wildrye is not tolerant of heavy grazing especially in late spring when the growing points are elevated 4 to 6 inches above the soil surface. For Loamy Bottom, basin wildrye should be the key species to manage and monitor.

Managing sagebrush steppe to improve the vigor and health of native bunchgrasses begins with an understanding of grass physiology. New growth for existing bunchgrasses begins each year from basal buds. Basin wildrye plants can expand via tillering, or new plants through natural reseeding. Regrowth from spring grazing comes mostly from photosynthesis.

During seed formation, the growing points of basin wildrye become elevated four to six inches and are vulnerable to damage or removal. Repeated grazing during late spring 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 to July 15). And each pasture should be rested the entire growing season every third year (approximately March 1 to July 15).

Basin wildrye 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

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

State and transition model

Custom diagram

Standard diagram

More interactive model formats are also available. View Interactive Models

More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective text

State 1
Reference Grassland Steppe with No Invasive Species

State 1 represents Alkali Terrace with no invasive or exotic species. All the functional, structural groups have one or more species. By cover saltgrass dominates the Reference Community By weight basin wildrye dominates the Reference Community Reference State Community Phases: 1.1 Reference Basin wildrye – Saltgrass 1.2 Rhizomatous Saltgrass – Basin wildrye Dominate Reference State Species: Basin wildrye, 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 1.1
Basin Wildrye and Saltgrass

65% basin wildrye
20% saltgrass
10% other native grasses

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

Community 1.2
Saltgrass and Basin Wildrye

25% basin wildrye
60% saltgrass
10% alkali cordgrass

Pathway 1.1A
Community 1.1 to 1.2

Result: Shift from Reference Community 1.1 (Basin Wildrye and Saltgrass) to Community 1.2 (Saltgrass and Basin Wildrye). Basin wildrye declines while saltgrass makes a corresponding increase. Also, alkali bluegrass declines and alkali cordgrass increases. Primary Trigger: Excessive grazing pressure (heavy grazing intensity, season long grazing or frequent late spring grazing) to basin wildrye. Ecological process: with consistent defoliation pressure basin wildrye and has low vigor, shrinking crowns and some mortality. Saltgrass rhizomes move into the areas vacated by basin wildrye and new saltgrass shoots become established.

Pathway 1.2A
Community 1.2 to 1.1

Result: Shift from rhizomatous grass community 1.2 back to Reference Community 1.1 with more bunchgrasses. Primary Trigger: Light to moderate grazing especially during dormant season, coupled with favorable moisture years allows basin wildrye to expand. Ecological process: Given the opportunity (good vigor and adequate soil moisture) basin wildrye plants gain the competitive edge and re-establishes dominance via tillering and new seedlings.

State 2
Invasive Species

State 2 represents Alkali Terrace where invasive broadleaf weeds and/or invasive annual grasses have prominence. Basin wildrye is all but missing and saltgrass remains as a patchwork of spots and clumps. State 2 can have two variations, both with or without rabbitbrush: 1. Broadleaf annual or biennial weeds with saltgrass patches 2. Annual grasses with saltgrass patches Community Phases for State 2: Invasive broadleaf annual or biennial weeds with patches of saltgrass Invasive annual grasses with patches of saltgrass Some Invasive Species in State 2: cheatgrass slender cinquefoil rabbitsfoot grass foxtail barley perennial pepperweed

Community 2.1
Invasive Species

Invasive annual and biennial broadleaf weeds with or without rabbitbrush
Foxtail barley

State 3
Seeded Grasses

State 3 represents a site that has been seeded to desirable grasses such as basin wildrye, beardless wildrye, tall wheatgrass, or western wheatgrass. Community Phases for State 3: 3.1 Seeded Grass 3.2 Shrub – Seeded Grass

Community 3.1
Seeded Grasses

85% seeded grasses

Community 3.2
Shrubs and Seeded Grasses

50% shrubs
40% seeded grasses

Pathway 3.1A
Community 3.1 to 3.2

Result: Shift from Community 3.1 Seeded Grasses to community 3.2 Shrub and Seeded Grasses. Primary Trigger: Grazing pressure (heavy intensity, season long grazing, frequent late spring grazing) to desirable seeded grasses. Ecological Process: with consistent grazing pressure, seeded grasses have poor vigor, shrinking crowns and some mortality. Rabbitbrush seed which blows onto the site establishes a crop of seedlings. Rabbitbrush cover expands as the shrubs grow.

Pathway 3.2A
Community 3.2 to 3.1

Result: Shift from Community 3.2 shrub-seeded grasses to Community 3.1 seeded grasses Primary Trigger: chemical spraying to kill rabbitbrush coupled with proper grazing management. A good remnant population of basin wildrye in good vigor is required to respond to the herbicide treatment. Ecological Process: chemical spray kills rabbitbrush plants and this release resources. Basin wildrye expands via tillering and new seedlings.

Transition T1A
State 1 to 2

Result: Shift from Reference State to State 2 with invasive species Primary Trigger: Grazing pressure (heavy intensity, season long grazing, frequent late spring grazing) to basin wildrye. Ecological process: with consistent grazing pressure basin wildrye has poor vigor, shrinking crowns and mortality. Initially, saltgrass increases but then declines with further grazing pressure. Invasive species colonize and as the deterioration continues, eventually dominate the site. Indicators: Increasing gaps between basin wildrye plants, decreasing cover of saltgrass and increasing cover of invasive species.

Restoration pathway R2A
State 2 to 3

Transition from State 2, a community dominated by invasive annual species, to State 3, which is predominately desirable seeded grasses. Species selection for the seeding is critical as the site is moderately saline-sodic. This restoration transition does not occur without significant time and inputs to control weeds, prepare a seedbed, seed desirable species, and post-seeding weed control and management. It may take two years or longer to kill invasive annual species and remaining saltgrass, and to exhaust the seedbank of invasive weed seeds. Care must be taken to maintain soil structure so that the seedbed has many safe-sites for the seed. Seed placement must be managed to achieve seed-soil contact at a very shallow depth (about 1/8 inch is desired). Species that can tolerate the saline-sodic conditions include basin wildrye, beardless wildrye, tall wheatgrass, and western wheatgrass. Proper grazing management is essential to maintain the stand post-seeding. The actual transition occurs when the seeded species have successfully established and are outcompeting the annual species for cover and dominance of resources.

Transition T3A
State 3 to 2

Result: Shift from State 3 seeded grasses to State 2 with invasive species Primary Trigger: Grazing pressure (heavy intensity, season long grazing, frequent late spring grazing) to desirable seeded grasses. Ecological Process: with consistent grazing pressure desirable grasses have poor vigor, shrinking crowns and mortality. This allows invasive species to colonize and then expand to a position of dominance. Indicators: increasing gaps between basin wildrye plants, increasing cover of invasive species

Additional community tables

Table 7. Community 1.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)
Shrub/Vine
1	Sprouting Shrubs - Trace			0–
	rabbitbrush	CHRYS9	Chrysothamnus	–	–
	greasewood	SAVE4	Sarcobatus vermiculatus	–	–
Grass/Grasslike
2	Dominant Tall Bunchgrass			2600–
	basin wildrye	LECI4	Leymus cinereus	–	–
3	Other Native Grasses - Minor			400–
	Sandberg bluegrass	POSE	Poa secunda	–	–
	alkali cordgrass	SPGR	Spartina gracilis	–	–
4	Dominant Rhizomatous Warm Season Grass			810–
	saltgrass	DISP	Distichlis spicata	–	–
5	Other Graminoids - Minor			150–
	clustered field sedge	CAPR5	Carex praegracilis	–	–
Forb
6	Native Forbs - Minor			150–
	common yarrow	ACMI2	Achillea millefolium	–	–

Table 8. Community 1.2 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 9. Community 2.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 10. Community 3.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 11. Community 3.2 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Supporting information

Inventory data references

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

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	05/12/2025
Approved by
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:

Download reference sheet

Natural ResourcesConservation Service