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

Major Land Resource Area (MLRA): 006X–Cascade Mountains, Eastern Slope.

Stretching from northern Washington to southern Oregon, MLR A6 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

Common Resource Area (CRA) 6.7 - Grand Fir Mixed Forest

This LRU occurs predominantly on mountain slopes and plateaus. The soils are dominantly in the Andisols and Inceptisols taxonomic order. Soil parent materials are dominantly colluvium and residuum from igneous, sedimentary, and metamorphic rock, and glacial till, with a mantle or mixture of volcanic ash in the upper part. Taxonomic soil climate is a cryic temperature regime and xeric moisture regime with average annual precipitation of about 40 inches.

Other LRU'S where the site occurs:
CRA 6.1 - North Cascades Subalpine / Alpine
CRA 6.2 - Pasayten / Sawtooth Highland
CRA 6.3 - Okanogan Pine / Fir Hills
CRA 6.4 - Chelan Tephra Hills

Classification relationships

The ecological site relates to the Wenatchee National Forest plant association: western hemlock/Cascade Oregongrape

Ecological site concept

This ecological site typically resides on mountain slopes, at elevations of 3000 to 5400 feet on slopes of 8 to 65 percent. The climatic conditions are moderately moist and cool, with 40 to 85 frost-free days, mean annual precipitation of 40 to 60 inches, and mean annual air temperature of 41 to 45 degrees Fahrenheit. This ecological site represents the drier end of the western hemlock zone.

The soils are dominantly Andisols, specifically Xeric Vitricryands, with an ashy-skeletal particle-size class. Surface textures are typically ashy sandy loam and ashy loamy sand. The parent material is volcanic ash over colluvium and residuum from volcanic and sedimentary rock. The soils are dominantly well drained, and have no flooding, ponding or water table. They are typically 20 to greater than 60 inches deep to a root-restricting feature. These soils have a cryic soil temperature regime and xeric soil moisture regime.

The reference community has an overstory of TSHE and THPL with moist adapted understory. Seral species include PIMO3, PIPO, PICO, PSME at the warmer, drier lower elevations and ABAM, ABGR, LAOC, PICO at colder, higher elevations. The understory can include: ACTR, ARNE, CAGE2, CHUM, GOOB2, MANE2, PAMY, ROSA5, SPBEL, VASC, CLUN2, LIBOL, PTAQP2. MANE2 generally dominates throughout the series.

Abies grandis generally occurs in this site for 100 years and ACCI though present, lasts only ten years. Generally, ABAM occurs in more maritime sites while ABGR in warmer, continental climate areas. Fire is the main disturbance regime and occurs as rare, stand replacement events on a rotational interval of 100 to 200 years. Specifically, USFS FEIS states that TSHE in the Pacific Northwest has a fire return interval of 150 to 400 years, though in Wenatchee NF it is thought to be 100 to 200 years based on stand ages, and LANDFIRE BPS states all fire types occur in 400 year intervals, and that stand replacing severity is 99 percent of all fires. Diseases that occur on this site include: Laminated (Armillaria, Annosum) root rots, brown cubical rot, dwarf mistletoe.

Associated sites

Similar sites

Table 1. Dominant plant species