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.

Classification relationships

Forested Plant Associations of the Oregon East Cascades (Simpson 2007)
Plant association group - Abies concolor/Abies grandis, Wet

Landfire Biophysical Setting (Landfire 2007)
0710180 East Cascades Mesic Montane Mixed-Conifer Forest and Woodland

Ecological site concept

This site represents a broad group of cool, moist grand fir forest communities on north and east slopes of the foothills surrounding Mount Hood. Occupying areas adjacent to and within the Columbia river valley, the climate of this site is influenced by a modified maritime climate as well as the rain shadow effect of Mount Hood, which alter plant community composition and productivity. The near sea level conduit of the Columbia river brings increased precipitation and low elevation cloud cover in winter that increases winter temperatures, relative to nearby areas outside of this influence.
The forest canopy of this site is dominated by Douglas-fir, grand fir, with ponderosa pine (Pinus ponderosa) sometimes common, and Douglas-fir (Pseudotsuga menziesii) and grand fir (Abies grandis) reproduction common in the understory. The plant community includes shrubs such as vine maple (Acer circinatum), serviceberry (Amelanchier alnifolia), oceanspray (Holodiscus discolor) and California hazel (Corylus cornuta); and herbaceous species such as vanilla leaf (Achlys triphylla), starflower (Trientalis borealis), pinegrass (Calamagrostis rubescens) and western fescue (Festuca occidentalis).
Nearby sites receiving less precipitation, or experiencing higher temperatures, are subject to decreased moisture availability in summer and therefore may support a reference community dominated by ponderosa pine and Douglas-fir, with few grand fir. Cooler and wetter sites upslope from this site support western hemlock (Tsuga heterophylla) and are subject to longer fire return due to higher fuel moisture later into the season.

This is a provisional ecological site that groups characteristics at a broad scale with little to no field verification and is subject to extensive review and revision before final approval. All data herein was developed using existing information and literature and should be considered provisional and contingent upon field validation prior to use in conservation planning.

Associated sites

Similar sites

Table 1. Dominant plant species