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, the Cascade Mountains, Eastern Slope, spans the entirety of 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 rainshadow 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-Cretaceaus 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 a high, cold volcanic plateau with nearly level topography interspersed with numerous cinder cones. The defining characteristic of this unit is the thick mantle of geologically recent pumice and ash deposited by the eruptions of Mount Mazama and Newberry Caldera. These soils are often coarse textured, excessively drained and have low thermal conductivity and fertility. These qualities promote low botanical diversity and the dominance of relatively few tree, shrub and herbaceous species. Forests are dominated by lodgepole pine in flat areas where cold air pools and depressions with seasonal water tables; ponderosa pine on warmer slopes and rises with improved cold air drainage; and occasionally white fir or shasta red fir at higher elevations receiving greater precipitation. Dense stands of lodgepole pine promote a fire regime characterized by occasional stand replacing fires, whereas more open stands of ponderosa may experience more frequent, low severity fire. The climate of this unit is cold and dry with a soil climate defined by a cryic temperature regime and a xeric moisture regime. Geologically, vulcanism predominates with Quaternary deposits from Mount Mazama and Newberry Caldera in the west and north and Late Tertiary deposits from the Winema volcanic field and Bald mountain in the south and east.

Classification relationships

Forested Plant Associations of the Oregon East Cascades (Simpson 2007)
PICO dry Plant association group
CLS211 – Lodgepole pine/Bitterbrush/Western needlegrass
CLS214 - Lodgepole pine/Bitterbrush/Idaho fescue

Plant Associations of the Central Oregon Pumice Zone (Volland 1985)
CLS211 – Lodgepole pine/Bitterbrush/Needlegrass

US Forest Service TEUI Ecological type
PICO/PUTR2/ACOC3 pumice Lapine

Ecological site concept

This site represents a lodgepole pine (Pinus contorta) dominant site commonly found within the pumice plateau of South Central Oregon. In comparison to other lodgepole dominant communities, this site occupies areas receiving less mean annual precipitation and with less access to subsurface groundwater sources. These conditions, as well as deep, excessively drained pumice soils, result in relatively sparse understories lacking diversity. The reference plant community is characterized by an open overstory of lodgepole pine and an understory dominated by bitterbrush (Purshia tridentata), with western needlegrass (Achnatherum occidentalis) often the only herbaceous species with significant cover. In comparison to other forest types, this site is generally too cool for ponderosa pine dominance and too dry for white fir (Abies concolor) dominance. This site often exists near to forest communities historically dominated by ponderosa pine and is distinguished abiotically from these sites by occupying colder areas that restrict ponderosa pine establishment on deep pumice soils. These areas often include upper elevations as well as basins and depressions with cold air pooling.

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

F006XY718OR