Natural Resources
Conservation Service
Ecological site R006XA302OR
Steep South Slopes 20-40 PZ
Last updated: 9/11/2023
Accessed: 11/14/2024
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): 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 woodland community at the transition zone between the eastside foothills of the Oregon Cascades and the Columbia plateau. The Reference Plant Community is an open stand of Oregon white oak (Quercus garryana) and ponderosa pine (Pinus ponderosa). The understory is characterized by a minor shrub component of antelope bitterbrush (Purshia tridentata) and deerbrush (Ceanothus integerrimus) with an herbaceous layer dominated by Idaho fescue (Festuca idahoensis) and bluebunch wheatgrass (Pseudoroegneria spicata). East cascade foothill plant communities are moisture limited and therefore highly influenced by aspect. This site occupies south slope aspects at the higher end of the precipitation range (20 to 40 in) for Oregon white oak on the east side of the Oregon cascades. South aspects increase evapotranspiration rates and steep slopes increase subsurface drainage of soil moisture within this precipitation zone, thereby allowing white oak to effectively compete with ponderosa pine. Sites with lower slope within this precipitation zone, are less influenced by aspect and therefore support higher canopy cover of ponderosa pine and Douglas-fir (Pseudotsuga menziesii). South aspect sites with shallower soils are dominated by perennial grasses with only occasional incidences of white oak.
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
F006XA804OR |
Mesic Xeric Maritime Foothills 30-50 PZ forested components within shared map units |
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R006XA204OR |
South Slopes 20-40 PZ shallower soils on south slopes |
Similar sites
R006XA204OR |
South Slopes 20-40 PZ shallower soils, white oak less common |
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R006XA304OR |
Loamy 20-40 PZ Non -aspect site, ponderosa pine and douglas-fir common |
R006XA200OR |
South Slopes 14-20 PZ lower effective precipitation |
Table 1. Dominant plant species
Tree |
(1) Quercus garryana |
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Shrub |
Not specified |
Herbaceous |
(1) Festuca idahoensis |
Click on box and path labels to scroll to the respective text.
T1A | - | Conversion of the site to agricultural use. |
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T2A | - | Invasion of annual grasses |
R2A | - | Extensive restoration activities |
R3A | - | Extensive restoration activities |
State 1 submodel, plant communities
1.1A | - | Time without fire |
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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 |
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3.1B | - | Time without fire |