Natural Resources
Conservation Service
Ecological site R011XY021OR
Shallow South Slopes
8-11 PZ
Last updated: 9/23/2020
Accessed: 08/16/2026
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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): 011X–Snake River Plains
Major Land Resource Area (MLRA): 011X – Snake River Plains
Precipitation or Climate Zone: 8-11” P.Z.Ecological site concept
Site does not receive additional moisture
Soils are:
Not saline or saline sodic
Shallow to moderately deep, with >35% coarse fragments (by volume) with a mixture of fragment sizes <3” and >3”, skeletal
not strongly or violently effervescent in the surface mineral 10”
Textures range from silt loam to silty clay loam in the surface mineral 4”
Slope is <30%
Clay content is =<35% in surface mineral 4”
Site does not have an argillic horizon with >35% clayAssociated sites
R011XY012OR Silty 8-11 PZ
Silty 8-11 PZ (non-aspect, higher production)
R011XY013OR Clayey 8-11 PZ
Clayey 8-11 PZ (non-aspect, different composition)
R011XY016OR Sandy 8-11 PZ
Sandy 8-11 PZ (non-aspect, different composition)
R011XY018OR Shallow Loam 8-11 PZ
Shallow Loam 8-11 PZ (non-apect, different composition)
R011XY032OR Silty North Slopes 8-11 PZ
Silty North Slopes 8-11 PZ (north aspect, different composition)
R011XY034OR Sandy North Slopes 8-11 PZ
Sandy North Slopes 8-11 PZ (north aspect, different composition)
Similar sites
R011XY018OR Shallow Loam 8-11 PZ
Shallow Loam 8-11 PZ (non-aspect, higher production, different composition – Thurber’s needlegrass dominant)
Table 1. Dominant plant species
Tree Not specified
Shrub (1) Artemisia tridentata ssp. wyomingensis
(2) Grayia spinosaHerbaceous (1) Pseudoroegneria spicata ssp. inermis
(2) Achnatherum thurberianumPhysiographic features
This site occurs on south aspects of low elevation terraces in the Malheur, Owyhee and adjacent Snake River drainage. Slopes typically range from 12 to 60%. Elevations vary from 2,100 to 3,200 feet.
Table 2. Representative physiographic features
Landforms (1) Terrace
Elevation 2100 – 3200 ft Slope 12 – 60 % Aspect SE, S, W Climatic features
The annual precipitation ranges from 8 to 11 inches, most of which occurs in the form of rain during the months of December through April. The soil temperature regime is mesic with a mean air temperature of 53 degrees F. Temperature extremes range from 110 to -10 degrees F. The frost free period ranges from 150 to 190 days. The optimum growth period for plant growth is late March through June.
Table 3 Representative climatic features
Frost-free period (average) 190 days Freeze-free period (average) Precipitation total (average) 10 in ">Influencing water features
Soil features
The soils of this site are typically shallow to very shallow and well drained. Typically the surface layer is a silt loam to a very fine sandy loam 2 to 6 inches thick. The subsoil is a silt loam to silty clay loam 6 to 12 inches thick. Depth to lacustrine or alluvial sediments ranges from 8 to 20 inches. An indurate pan is often present. Permeability is moderate. The available water holding capacity (AWC) is about 2 to 4 inches for the profile. The erosion potential is moderate to severe.
Table 4. Representative soil features
Parent material (1) Loess – rhyolite
Surface texture (1) Silt loam
(2) Very fine sandy loam
Family particle size (1) Loamy
Drainage class Well drained Permeability class Moderate Soil depth 6 – 20 in Available water capacity
(0-40in)2 – 4 in Ecological dynamics
The potential native plant community is dominated by Wyoming big sagebrush, spiny hopsage and beardless wheatgrass. Thurber’s needlegrass is prominent. Sandberg bluegrass is the dominant shallow rooted perennial grass. A variety of forbs and shrubs are present. Vegetative composition of the community is approximately 75 percent grasses, 10 percent forbs and 15 percent shrubs. The approximate ground cover is 50 to 60 percent (basal and crown).
Range in Characteristics:
Wyoming big sagebrush increases at the upper end of the precipitation zone and spiny hopsage at the lower end. Beardless wheatgrass increases on silty surfaces. Thurber’s needlegrass increases on a very fine sandy loam surfaces and on droughtier sites. Needle and thread is present on coarser surfaces. Sandberg bluegrass increases on silty surfaces in association with a strong microbiotic crust. Production increases at the upper end of the precipitation zone.
Response to Disturbance:
Disturbances that impact the condition of this site include overgrazing by large ungulates, fire, droughts that impact the hydrologic functions of these low-lying sites, and outside anthropogenic impacts that affect site hydrology which will impact water availability for the reference plants. Any disturbance that continues long enough or is of great enough severity will reduce reference plant vigor and cover rapidly.
When the condition of the site deteriorates as a result of over grazing beardless wheatgrass and Thurber’s needlegrass rapidly decreases. Wyoming big sagebrush, spiny hopsage and Sandberg bluegrass increase. Cheatgrass, other annuals and biennial weeds rapidly invade. With fire and continued disturbance Wyoming big sagebrush is severely impacted. Rabbitbrush increases slightly and annuals and noxious biennial forbs strongly invade. Bare ground increases and excessive erosion contributes to downstream sedimentation. The excessive erosion is most pronounced in drainage areas where deep incised gulley’s form.
States: ARTRW/POSE-BRTE (degraded without fire); BRTE/biennial forbs or POSE-POBU/biennial forbs (following fire on degraded range)
**The State-and-Transition Model represents only the Reference Plant Community phase due to limited time, data, and literature support at the time of development. Future work will be needed to describe dynamics, alterative states and land use models.State and transition model
More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective textEcosystem states
State 1 submodel, plant communities
State 1
Historic Climax Plant CommunityCommunity 1.1
Reference Plant CommunityThe reference plant community is dominated by Wyoming big sagebrush, spiny hopsage and beardless wheatgrass. Thurber’s needlegrass is prominent. Sandberg bluegrass is the dominant shallow rooted perennial grass. A variety of forbs and shrubs are present. Vegetative composition of the community is approximately 75 percent grasses, 10 percent forbs and 15 percent shrubs. The approximate ground cover is 50 to 60 percent (basal and crown).
Figure 1. Annual production by plant type (representative values) or group (midpoint values)
Table 5. Annual production by plant type
Plant type Low
(lb/acre)Representative value
(lb/acre)High
(lb/acre)Grass/Grasslike 150 300 525 Shrub/Vine 30 60 105 Forb 20 40 70 Total 200 400 700 Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 Dominant, perennial, moderate rooted bunchgrass 200–240 beardless wheatgrass PSSPI Pseudoroegneria spicata ssp. inermis 200–240 – 2 Sub-dominant, moderate rooted bunchgrass 80–120 Thurber's needlegrass ACTH7 Achnatherum thurberianum 80–120 – 3 Other moderate rooted bunchgrasses 20–80 needle and thread HECO26 Hesperostipa comata 12–32 – bluebunch wheatgrass PSSPS Pseudoroegneria spicata ssp. spicata 8–20 – foxtail wheatgrass PSSA2 ×Pseudelymus saxicola 0–12 – Indian ricegrass ACHY Achnatherum hymenoides 0–12 – squirreltail ELEL5 Elymus elymoides 5–12 – 4 Shallow rooted bunchgrass 8–20 Sandberg bluegrass POSE Poa secunda 8–20 – Forb8 Dominant, perennial forbs 28–52 arrowleaf balsamroot BASA3 Balsamorhiza sagittata 8–12 – fleabane ERIGE2 Erigeron 4–8 – buckwheat ERIOG Eriogonum 4–8 – desertparsley LOMAT Lomatium 4–8 – phlox PHLOX Phlox 4–8 – common yarrow ACMI2 Achillea millefolium 4–8 – 9 Other perennial forbs 12–40 Indian paintbrush CASTI2 Castilleja 0–4 – Douglas' dustymaiden CHDO Chaenactis douglasii 0–4 – bastard toadflax COMAN Comandra 0–4 – hawksbeard CREPI Crepis 2–4 – common woolly sunflower ERLA6 Eriophyllum lanatum 0–4 – haplopappus HAPLO11 Haplopappus 0–4 – povertyweed IVAX Iva axillaris 0–4 – western stoneseed LIRU4 Lithospermum ruderale 0–4 – woodland-star LITHO2 Lithophragma 1–4 – lupine LUPIN Lupinus 0–4 – hoary tansyaster MACA2 Machaeranthera canescens 0–4 – plains pricklypear OPPO Opuntia polyacantha 0–4 – beardtongue PENST Penstemon 0–4 – scarlet globemallow SPCO Sphaeralcea coccinea 0–4 – milkvetch ASTRA Astragalus 2–4 – mariposa lily CALOC Calochortus 0–2 – onion ALLIU Allium 1–2 – pussytoes ANTEN Antennaria 1–2 – deathcamas ZIGAD Zigadenus 0–2 – Shrub/Vine11 Dominant, evergreen, non-sprouting shrub 20–60 12 Sub-dominant, deciduous, non-sprouting shrub 20–40 spiny hopsage GRSP Grayia spinosa 20–40 – 15 Other shrubs 8–32 rubber rabbitbrush ERNA10 Ericameria nauseosa 5–12 – littleleaf horsebrush TEGL Tetradymia glabrata 0–8 – broom snakeweed GUSA2 Gutierrezia sarothrae 0–8 – Interpretations
Animal community
Livestock Grazing:
This site is suitable for livestock grazing use in the late fall, winter and early spring under a planned grazing system. Use should be postponed until the soils are firm enough to prevent trampling damage and soil compaction. Grazing management should be keyed for beardless wheatgrass and Thurber’s needlegrass. Deferred grazing or rest is recommended at least once every three years.
Native Wildlife Associated with the Potential Climax Community:
This site is commonly used by pronghorn antelope, mule deer, rabbits, rodents, upland birds and various predators. It is a preferred site for sage grouse wintering. Antelope and mule deer make excellent use of the site for winter and early spring forage.Hydrological functions
The soils of this site are typically in an upland topographic position. They have moderate runoff potential and medium infiltration rates when the hydrologic cover is high. Hydrologic cover is high when the beardless wheatgrass and Thurber’s needlegrass deep rooted bunchgrass component is greater than 70 percent of potential.
Supporting information
Contributors
A.BAHN/T.BLOOMER/E.PETERSON
T.Bloomer,E.Petersrn,A.BahnApproval
Kendra Moseley, 9/23/2020
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 08/16/2026 Approved by Approval date Composition (Indicators 10 and 12) based on Annual Production Indicators
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Number and extent of rills:
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Presence of water flow patterns:
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Number and height of erosional pedestals or terracettes:
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Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
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Number of gullies and erosion associated with gullies:
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Extent of wind scoured, blowouts and/or depositional areas:
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Amount of litter movement (describe size and distance expected to travel):
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Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
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Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
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Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
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Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
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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:
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Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
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Average percent litter cover (%) and depth ( in):
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Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
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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:
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Perennial plant reproductive capability:
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