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

This unit is characterized by ash mantled lava flows and glacial outwash plains on lower mountain slopes and foothills of the East Cascades in Oregon. Vegetation is largely dominated by forests of ponderosa pine with transitional dry mixed conifer forests where Douglas fir and grand fir are subdominant occurring in areas with greater effective precipitation.
Historically, these forests have been influenced by a fire regime whereby frequent to moderately frequent, low and mixed severity fires would have favored the development of open stands of mature ponderosa pine. The climate of this unit is cool and dry with a predominately xeric soil moisture regime and frigid soil temperature regime.
Geologically, underlying lithologies are dominated by Quaternary and late Tertiary basalt and basaltic andesite as well as mixed grain sediments deposited during Pleistocene glacial retreat. Unlike the nearby pumice plateau, this unit lacks the deep pumice soils that favor lodgepole pine and discourage Douglas-fir. This unit is south of the climate influences of the Columbia gorge and therefore does not support woodlands of Oregon white oak.

Classification relationships

Forested Plant Associations of the Oregon East Cascades (Simpson 2007)
CWS533 – white fir–grand fir/golden chinquapin

Plant Associations of the Central Oregon Pumice Zone (Volland 1985)
CWC211 - Mixed conifer/snowbrush-chinkapin/brackenfern

Plant Associations of the Commercial Forest of the Warm Springs Indian Reservation (Marsh 1987)
Mixed conifer - Snowberry
Mixed conifer - Chinkapin

Landfire Biophysical Setting (Landfire 2007)
0710450 - Northern Rocky Mountain Dry-Mesic Montane Mixed Conifer Forest

Ecological site concept

This site encompasses a broad group of dry mixed conifer communities on foothills and mountain slopes of the Eastern Cascades. The visual aspect of this site is a forest canopy dominated by a variable mixture of ponderosa pine (Pinus ponderosa) and Douglas fir (Pseudotsuga menziesii), with grand fir (Abies grandis) subdominant, and understory reproduction of Douglas fir and grand fir common.
The plant community often includes shrubs such as snowbrush (Ceanothus velutinus), greenleaf manzanita (Arctostaphylos patula), golden chinkapin (Chrysolepis chrysophylla) and snowberry (Symphoricarpos spp.) and herbaceous species such as pinegrass (Calamagrostis rubescens), brakenfern (Pteridium aquilinum) and starflower (Trientalis borealis). Nearby sites at lower elevations or occupying doughtier aspects experience less effective precipitation and support a reference community dominated by ponderosa pine and Douglas fir, with little grand fir. This is in part due to less effective moisture and higher temperatures and helps to facilitate a more frequent fire rotation.
Nearby sites at higher elevations or more northerly aspects host wet adapted tree species such as western hemlock, due to cooler temperatures and greater effective precipitation. These conditions facilitate a less frequent fire rotation. Since this site occupies a transition between these forest types, this site experiences a fire regime that may be intermediate between the two forest types or host a mosaic of the two types (Landfire fire regime groups 1 and 3). As such, the plant community of this site may attain many forms both structurally and compositionally depending on disturbance history and the influences of adjacent sites on its fire regime.

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

Legacy ID

F006XB801OR