Natural Resources
Conservation Service
Ecological site R006XA200OR
South Slopes
14-20 PZ
Last updated: 3/31/2025
Accessed: 08/06/2026
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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): 006X–Cascade Mountains, Eastern Slope
Stretching from northern Washington to southern Oregon, MLRA6 encompasses the mountain slopes, foothills, elevated plateaus and valleys on the eastern slopes of the Cascade mountains. This MLRA is a transitional area between the Cascade Mountains to the west and the lower lying Columbia Basalt Plateau to the east. Situated in the rain shadow of the Cascade Crest, this MLRA receives less precipitation than portions of the cascades further west and greater precipitation than the basalt plateaus to the east. Geologically, the majority of the MLRA is dominated by Miocene volcanic rocks, while the northern portion is dominated by Pre-Cretaceous metamorphic rocks and the southern portion is blanketed with a thick mantle of ash and pumice from Mount Mazama. The soils in the MLRA dominantly have a mesic, frigid, or cryic soil temperature regime, a xeric soil moisture regime, and mixed or glassy mineralogy. They generally are moderately deep to very deep, well drained, and loamy or ashy. Biologically, the MLRA is dominated by coniferous forest, large expanses of which are dominated by ponderosa pine, Douglas-fir or lodgepole pine. Areas experiencing cooler and moister conditions include grand fir, white fir, and western larch while the highest elevations include pacific silver fir, subalpine fir and whitebark pine. Economically, timber harvest and recreation are important land uses in these forests. Historically, many of these forests would have experienced relatively frequent, low and mixed severity fire favoring the development of mature forests dominated by ponderosa pine or Douglas-fir. In the southern pumice plateau forests, less frequent, higher severity fire was common and promoted the growth of large expanses of lodgepole pine forests.
LRU notes
Located at the eastern edge of the Columbia river gorge, this unit is restricted to areas influenced by the modified maritime climate of this unique passageway through the Cascades. This setting allows for the persistence of Oregon White Oak woodlands east of the Cascade crest. These woodlands often include ponderosa pine, and on sites with greater soil moisture, Douglas-fir. Botanical diversity is high, with a mixture of West Cascade and East Cascade plant species commonly co-occurring. Physiographically, this unit is characterized by dissected foothills, valleys and ridges draining Mount Hood in Oregon and Mount Adams in Washington. Geologically, the unit is characterized by late tertiary pyroclastic and volcanoclastic deposits and basalt flows. The climate of this unit is generally warm and dry with a predominately xeric soil moisture regime and mesic soil temperature regime. Historically, the drier extent of these forests have been influenced by a fire regime whereby frequent low and mixed severity fires would have favored the development of open canopied forests. Higher elevations and more westerly locations receiving more moisture within this unit would have been influenced by moderately frequent, low and mixed severity fires favoring a mosaic of forest stages with closed canopy conditions common.
Ecological site concept
This site represents a dry woodland community at the transition zone between the foothills on the eastside of the Oregon cascades and the Columbia plateau. The Reference Plant community is that of an Oregon white oak (Quercus garryana) woodland with an understory of perennial native grasses such as Sandberg bluegrass (Poa secunda) and bluebunch wheatgrass (Pseudoroegneria spicata) and shrubs such as antelope bitterbrush (Purshia tridentata) and green rabbitbrush (Chrysothamnus viscidiflorus). East cascade foothill plant communities are moisture limited and therefore highly influenced by aspect. This site occupies south slopes at the lower end of the precipitation range for Oregon white oak (14 to 20 in). Increased evapotranspiration as a result of south aspects create conditions favorable for white oak dominance on this site. This is in contrast to adjacent sites with more gentle slopes and higher precipitation (20 to 40 in) which favor competition by conifers and therefore support higher density of ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii) in the stand. Sites on north aspects often retain higher soil moisture and therefore exhibit higher productivity and higher cover of Idaho fescue (Festuca idahoensis).
This is a provisional ecological site and is subject to extensive review and revision before final approval. All data herein should be considered provisional and contingent upon field validation prior to use in conservation planning.Associated sites
R006XA300OR Loamy 14-20 PZ
non-aspect positions, higher effective precipitation
Similar sites
R006XA300OR Loamy 14-20 PZ
Non aspect, ponderosa pine common
R006XA302OR Steep South Slopes 20-40 PZ
higher effective precipitation
Table 1. Dominant plant species
Tree (1) Quercus garryana
Shrub Not specified
Herbaceous (1) Pseudoroegneria spicata
(2) Poa secundaPhysiographic features
This site occurs on south, southeasterly, and west facing exposures of hill and mountain side slopes. Slopes range from 2 to 65 percent. Elevations typically range from 1,000 to 2,500 (350 to 750 meters) but may extend from 500 to 3,500 feet (150 to 1,050 meters). This site is not subject to ponding or flooding and no water table is present within 100 inches of the soil surface.
Table 2. Representative physiographic features
Landforms (1) Foothills > Hillside or mountainside
Flooding frequency None Ponding frequency None Elevation 1000 – 2500 ft Slope 2 – 65 % Ponding depth 0 in Water table depth 100 in Aspect W, SE, S, SW Table 3. Representative physiographic features (actual ranges)
Flooding frequency Not specified Ponding frequency Not specified Elevation 500 – 3500 ft Slope 0 % Ponding depth 0 in Water table depth 0 in Climatic features
This site has a xeric soil moisture regime with mean annual precipitation ranging from 14 to 20 inches (350 to 500mm), most of which occurs during the months of November through March in the form of rain and snow. The soil temperature regime is mesic with a mean annual air temperature of approximately 48 degrees Fahrenheit (9 degrees C). Historical temperature extremes range from 105 to -15 degrees F (40 to -26 degrees C). The frost-free period ranges from about 120 to 180 days. The optimum period for plant growth is mid-March through mid-July. This climate is modified by the influence of the Columbia River Gorge which acts as a conduit for maritime air masses to move past the Cascade mountains. The graphs below are populated from the closest available weather station to representative site locations and are provided to indicate general climate patterns.
Table 4 Representative climatic features
Frost-free period (characteristic range) 120-180 days Freeze-free period (characteristic range) Precipitation total (characteristic range) 10-20 in Frost-free period (average) 150 days Freeze-free period (average) Precipitation total (average) 20 in Characteristic rangeActual rangeBarLineFigure 1. Monthly precipitation range
Characteristic rangeActual rangeBarLineFigure 2. Monthly minimum temperature range
Characteristic rangeActual rangeBarLineFigure 3. Monthly maximum temperature range
BarLineFigure 4. Monthly average minimum and maximum temperature
Figure 5. Annual precipitation pattern
Figure 6 Annual average temperature pattern
Climate stations used
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(1) DUFUR [USC00352440], Dufur, OR
">Influencing water features
This site is not influenced by water from a wetland or stream.
Wetland description
N/A
Soil features
The soils of this site are typically shallow to deep to bedrock and well drained. Surface textures often range from silt loam to cobbly or stony loam. Subsoil textures often range from loam, cobbly loam or gravelly loam. The typical surface horizon is a cobbly loam about 5 inches thick. The subsoil is often a very cobbly loam or very cobbly clay loam about 13 inches thick. Depth to bedrock or an indurated pan ranges from 12 to 60 inches. Permeability is moderate to moderately slow. The available water holding capacity is about 5 to 12 inches for the profile.
Table 5. Representative soil features
Parent material (1) Loess
(2) Colluvium – volcanic rock
(3) Colluvium – sedimentary rock
Surface texture (1) Silt loam
(2) Cobbly, stony loam
Family particle size (1) Loamy
(2) Coarse-loamy
(3) Fine-loamy
Drainage class Well drained Permeability class Moderately slow to moderate Depth to restrictive layer 12 – 60 in Soil depth 12 – 60 in Surface fragment cover <=3" 0 – 45 % Surface fragment cover >3" 0 – 45 % Available water capacity
(0-60in)5 – 12 in Soil reaction (1:1 water)
(0-40in)6.6 – 7.3 Subsurface fragment volume <=3"
(4-60in)0 – 25 % Subsurface fragment volume >3"
(4-60in)0 – 20 % Table 6. Representative soil features (actual values)
Drainage class Not specified Permeability class Not specified Depth to restrictive layer 0 in Soil depth 0 in Surface fragment cover <=3" 0 % Surface fragment cover >3" 0 % Available water capacity
(0-60in)0 in Soil reaction (1:1 water)
(0-40in)5.6 – 8.4 Subsurface fragment volume <=3"
(4-60in)0 % Subsurface fragment volume >3"
(4-60in)0 % Ecological dynamics
Reference Plant community:
The Reference Plant Community of this site is characterized by an open, savannah-like woodland maintained by relatively frequent, low-intensity fires dominated by Oregon white oak and some ponderosa pine in the overstory. The dominant grass species is bluebunch wheatgrass (Pseudoroegneria spicata) with Sandberg bluegrass, bitterbrush and a variety of forbs also common in the stand. Vegetative composition of the community is approximately 85 percent grasses, 5 percent forbs and 10 percent shrubs/trees. Variability in plant composition and yield is dependent on aspect, soil depth, and coarse fragments, rather than on precipitation and elevation ranges that occur within the site. Idaho fescue will increase as aspect changes to more east facing.
Disturbance:
As one of the driest woodland types in Oregon, white oak - ponderosa pine communities on the eastside of the Cascades were historically subject to frequent, low severity fires that maintained the open, savannah-like appearance and higher cover of herbs in the understory, both due to natural and cultural ignitions (Landfire 2007). Mixed and stand replacement fires also occurred occasionally in these stands but were rare due to limited fuels and fire tolerant canopies (Landfire 2007). Oregon white oak is adapted to these conditions by re-sprouting from bases following top kill as well as developing thick, fire-resistant bark with maturity (Devine et al 2013). White oak is susceptible to mortality by low intensity fires when young, yet gains resistance with age. If fires are frequent enough, they can remove many of the young trees, leaving only those trees that managed to survive and continue growing (Landfire 2007). With a disruption of this fire regime, the canopy becomes more closed and the understory declines in cover and production (Devine et al. 2013). This white oak site may include some ponderosa pine which may compete effectively with oak for soil moisture and light on microsites yet the dry south slopes of this site will preclude conifer dominance overtime (Gucker 2007). As warm, dry, open, woodland communities, these white oak sites may be highly susceptible to invasive plant species introductions (Lillybridge et al 1995). Common invasive plant species include cheatgrass (Bromus tectorum), diffuse knapweed (Centaurea diffusa), and bulbous bluegrass (Poa bulbosa).
This site may be used for livestock grazing, with bluebunch wheatgrass as the preferred species during spring and summer. Overgrazing may result in a decrease in bluebunch wheatgrass and Idaho fescue, and an increase in Sandberg bluegrass. With further deterioration, annual forbs increase and annual grasses invade, possibly altering the fire regime (Gucker 2007). Under deteriorated conditions bare ground increases. Excessive erosion in the bare interspaces markedly reduces the site potential and contributes to downstream sedimentation. These effects may be intensified when soil moisture is high, a condition and increases the susceptibility of these soils to erosion and compaction by grazing animals.
The state and transition model below represents a generalized and simplified version of plant community change in response to major disturbance types in this ecological site. It does not attempt to model all of the complex interacting effects of grazing, fire and invasive species on ecosystem change and the potential restoration pathways emerging from these dynamics. Emerging evidence is suggesting that climate change is leading to hotter and drier conditions in western forests that will increase fire frequency and extent and lengthen fire seasons (Halofsky et al. 2020). When combined with the interacting impacts of fire suppression, drought, and insect outbreaks, it is possible that this ecological system will experience unpredictable ecosystem shifts and additional alternative states. For warm and dry sites, these impacts may include the possibility of regeneration failure following wildfire disturbance (Halofsky et al. 2020). As this site is updated in future iterations, and further research informs our understanding of East Cascades oak woodlands, descriptions will include more thorough treatments of disturbance and ecological change. The Reference State is largely based on Landfire biophysical settings model 710600: East Cascades Oak-Ponderosa Pine Forest and Woodland (Landfire 2007).State and transition model
Custom diagramStandard 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 textEcosystem states
T1A - Conversion of the site to agricultural use. T2A - Invasion of annual grasses R2A - Extensive restoration R3A - Restoration activities State 1 submodel, plant communities
1.1A - Time without fire 1.2B - High severity, stand replacing fire occurs 1.2A - Time without fire 1.3A - High severity, stand replacing fire occurs State 3 submodel, plant communities
3.1A - High severity, stand replacing fire occurs 3.1B - Time without fire State 1
Historic ReferenceThe Reference Plant Community is an open, mature, white oak savannah represented by Community Phase 1.3. This is the most advanced community within the historical disturbance regime for this site, yet this site occurs across the landscape as a mosaic of plant community phases characterized by variation in community structural stage (tree age, density and cover) and species composition. Historically, Oregon white oak woodlands would have cycled from a stand initiation phase (1.1) to a young woodland phase (1.2) to a mature woodland phase (1.3) with a disturbance regime characterized by frequent, low intensity surface fires with occasional mixed or replacement severity fires (Landfire fire regime group 1). Fire suppression has likely diminished the presence of mature savannah across the landscape, instead favoring closed canopy conditions and higher densities of younger trees (Devine et al. 2013). Given the likelihood that this state, even in the best condition and highest potential, will almost always include at least some component of exotic species regardless of management inputs, this may also be referred to as the “Current Potential State”. In this document, the term “reference state” is used synonymously with “current potential state” for the sake of simplicity. As a south aspect site, this site may have lower resistance and resilience to invasion by exotic plant species compared to adjacent sites.
Dominant plant species
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Oregon white oak (Quercus garryana), tree
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bluebunch wheatgrass (Pseudoroegneria spicata), grass
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Sandberg bluegrass (Poa secunda), grass
Community 1.1
Bunchgrass/ShrubSite characterized by bunchgrasses, shrubs and white oak sprouting as coppice from bases. Heavy herbivory or frequent fire will maintain the community in this phase.
Community 1.2
Young woodlandYoung stand characterized by an open overstory of intermediate aged oak and an understory of bunchgrasses and shrubs. Regular surface fire will maintain the community in this phase. Frequent low severity fires in this stage will maintain the overstory of older pole sized oak trees, kill young trees and saplings and an facilitate an understory dominated by herbaceous species and sprouting shrubs.
Community 1.3
Reference Community, Mature woodlandThis is the Reference Community. Mature stand characterized by an open overstory of mature, mostly multi-stemmed oaks with bunchgrasses, shrubs and perennial grasses in the understory. Regular surface fire will maintain the community in this phase. Frequent low severity fires in this stage will maintain the overstory of older pole sized oak trees, kill young trees and saplings and an facilitate an understory dominated by herbaceous species and sprouting shrubs.
Figure 7. Annual production by plant type (representative values) or group (midpoint values)
Table 7. Annual production by plant type
Plant type Low
(lb/acre)Representative value
(lb/acre)High
(lb/acre)Grass/Grasslike 360 600 760 Tree 45 75 95 Forb 23 38 48 Shrub/Vine 23 38 48 Total 451 751 951 Pathway 1.1A
Community 1.1 to 1.2Time without fire
Pathway 1.2B
Community 1.2 to 1.1High severity, stand replacing fire occurs
Pathway 1.2A
Community 1.2 to 1.3Time without fire
Pathway 1.3A
Community 1.3 to 1.1High severity, stand replacing fire occurs
State 2
Cropland or PasturelandIn this state the site is used for agricultural production. This may include perennial pasture or annual crops.
Dominant plant species
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orchardgrass (Dactylis glomerata), grass
State 3
InvadedIn this state the site is invaded by exotic annual grasses which at high levels may create positive feedbacks that alter fire regimes and promote prolonged invasion.
Dominant plant species
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cheatgrass (Bromus tectorum), grass
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medusahead (Taeniatherum caput-medusae), grass
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bulbous bluegrass (Poa bulbosa), grass
Community 3.1
Invaded WoodlandSite characterized by an oak woodland that includes a significant portion of invasive annual grasses that have sufficient cover to alter the fire regime and reduce understory biodiversity. Fires become more frequent and may be shifted earlier into the season.
Community 3.2
Bunchgrass/shrub, InvadedSite characterized by invasive annual grasses within the understory composition, bunchgrasses are reduced, shrubs reestablishing and white oak sprouting as coppice from bases. Frequent fire will maintain the community in this phase.
Pathway 3.1A
Community 3.1 to 3.2High severity, stand replacing fire occurs
Pathway 3.1B
Community 3.2 to 3.1Time without fire
Transition T1A
State 1 to 2Conversion of the site to agricultural use.
Transition T2A
State 1 to 3Invasion of annual grasses, such as cheatgrass and bulbous bluegrass, occupying a significant amount of ground cover. Research has not identified a threshold for cover that will shift this community into an alternative state.
Restoration pathway R2A
State 2 to 1Restoration of this site will likely be time and labor intensive and require significant inputs. Possible restoration activities will be site specific and may be informed by Devine et al. 2013.
Restoration pathway R3A
State 3 to 1Reduction of invasive species may be possible yet will be time and labor intensive and require significant inputs. Possible restoration activities will be site specific and may be informed by Devine et al. 2013.
Additional community tables
Table 8. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 9. Community 1.2 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 10. Community 1.3 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 Grass and Grasslike plants 340–690 bluebunch wheatgrass PSSPS Pseudoroegneria spicata ssp. spicata 295–560 – Sandberg bluegrass POSE Poa secunda 50–130 – Idaho fescue FEID Festuca idahoensis 5–15 – 2 Other perennial grasses 5–40 Thurber's needlegrass ACTH7 Achnatherum thurberianum 0 – prairie Junegrass KOMA Koeleria macrantha 0 – squirreltail ELEL5 Elymus elymoides 0 – Geyer's sedge CAGE2 Carex geyeri 0 – 3 Big Bluegrass 5–15 Sandberg bluegrass POSE Poa secunda 5–15 – Forb4 Forbs 10–30 arrowleaf balsamroot basa3 Balsamorhiza sagittata 5–15 – common yarrow acmi2 Achillea millefolium 5–15 – 5 Other perennial forbs 5–40 arrowleaf buckwheat ERCO12 Eriogonum compositum 0 – desertparsley lomat Lomatium 0 – lupine lupin Lupinus 0 – pussytoes anten Antennaria 0 – Douglas' dustymaiden chdo Chaenactis douglasii 0 – onion alliu Allium 0 – Scouler's woollyweed hisc2 Hieracium scouleri 0 – Tree6 Trees 25–115 Oregon white oak quga4 Quercus garryana 35–75 – ponderosa pine pipo Pinus ponderosa 5–35 – Shrub/Vine7 Shrubs 15–75 antelope bitterbrush putr2 Purshia tridentata 5–35 – rubber rabbitbrush ERNA10 Ericameria nauseosa 5–20 – deerbrush CEIN3 Ceanothus integerrimus 5–15 – Table 11. Community 3.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 12. Community 3.2 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Supporting information
Inventory data references
Information presented here has been derived from NRCS data. Field observations from range trained personnel were also used. Other sources used as references include USDA NRCS Water and Climate Center, USDA NRCS National Range and Pasture Handbook, and USDA NRCS Soil Surveys from various counties.
References
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1980. Fire Effects Information System. http://www.fs.fed.us/database/feis/.
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. 2021 (Date accessed). USDA PLANTS Database. http://plants.usda.gov.
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1980. USNVC [United States National Vegetation Classification]. 2019. United States National Vegetation Classification Database, V2.03. Federal Geographic Data Committee, Vegetation Subcommittee, Washington DC.. USNVC: http://usnvc.org/.
Other references
Devine, W.; Bower, A.; Miller, J.; Aubry, C. 2013. Oregon white oak restoration strategy for National Forest System lands east of the Cascade Range. Olympia, WA: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 97 p.
Gucker, Corey L. 2007. Quercus garryana. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.fed.us/database/feis/plants/tree/quegar/all.html [2020, June 2].
Halofsky, J.E., Peterson, D.L. & Harvey, B.J. Changing wildfire, changing forests: the effects of climate change on fire regimes and vegetation in the Pacific Northwest, USA. fire ecol 16, 4 (2020). https://doi.org/10.1186/s42408-019-0062-8
LANDFIRE, 2007, Biophysical Settings Model Descriptions, LANDFIRE 1.1.0, U.S. Department of the Interior, USDA Forest service, Accessed 20 April 2020 at https://www.landfire.gov/bps-models.php
Lillybridge, T.R.; Kovalchik, B.L.; Williams, C.K.; Smith, B.G. 1995. Field guide for forested plant associations of the Wenatchee National Forest. Gen. Tech. Rep. PNW-GTR-359. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 335 p.
Simpson, M. 2007. Forested plant associations of the Oregon East Cascades. Portland, Or. U.S. Dept. of Agriculture, Forest Service, Pacific Northwest Region.Contributors
Andrew Neary - 2020/2021 update of original draft concept
Approval
Kirt Walstad, 3/31/2025
Acknowledgments
Development of this site as a range site was based on field data collection completed in 1989. It was revised and updated with information regarding ecological dynamics in 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 03/31/2025 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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