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): 003X–Olympic and Cascade Mountains

The Cascade and Olympic Mountains (MLRA 3) include the west slope and parts of the east slope of the Cascades Mountains in Washington and Oregon. The Olympic Mountains in Washington State are also included. These mountains are part of a volcanic arc located at a convergent plate boundary. Volcanic rocks predominate but metamorphic and sedimentary rocks occur in the North Cascades and Olympic Mountains. Topography is generally dissected and steep, but some areas consist of constructional volcanic platforms and isolated stratovolcanoes. Elevation is usually 500 to 6000 feet but reaches to 14,410 ft at the summit of Mount Rainier. Many areas hosted alpine glaciers or ice sheets during the Pleistocene, and a few remain today.
Climate becomes cooler and moister with increasing elevation and latitude. Low elevations experience a long growing season and mild temperatures. High elevations can accumulate snowpack lasting into summer and frost may occur in any month. Average annual precipitation ranges from 60 to 180 inches in most areas. Most precipitation falls during the fall, winter, and spring during low-intensity frontal storms. Summers are relatively dry. Average annual temperature is 27 to 50 degrees F. The frost-free period is 10 to 180 days.

LRU notes

The Mazama Cascades land resource unit (LRU F) is located in south-central Oregon, at the southern end of MLRA 3. Like the High Cascades (LRU D), it occurs on the young volcanic platform straddling the crest of the Cascade Mountains. Most areas are mantled with pumice and coarse volcanic ash from the eruption of Mount Mazama (Crater Lake), but areas outside the Mazama ash zone have finer ash from other sources. Mean annual precipitation is generally lower than in areas to the north. This area is approximately bounded by Waldo Lake on the north and Aspen Butte located in Winema National Forest on the south. Frequent-fire forests with a xeric soil moisture regime lie to the east and west. Major rivers draining this area include the Willamette, Umpqua, Rogue, Deschutes, and Klamath.
Bedrock consists mainly of Plio-Pleistocene lavas (Orr, et al. 1992). Topography is gentle and undissected compared with the Western Cascades (LRU E). Large areas were covered in an alpine ice-sheet during the Pleistocene (Noller, et al. 2016). Till often lies above volcanic bedrock. Many areas were mantled with coarse volcanic ash and pumice from the Holocene eruption of Mount Mazama, but some were not.
Soil moisture regime is udic or aquic. Soils have a cryic or frigid soil temperature regime. Mean annual precipitation is typically 30 to 80 inches. Andisols and Spodosols are common soil orders. Soils within the Mazama pumice zone (coarse ash and pumice) typically meet andic soil properties required characteristics 3, while soils outside the pumice zone usually meet only required characteristics 2 (Soil Survey Staff, 2014).
Due to low thermal conductivity, pumice soils may experience extreme diurnal temperature fluctuations at the soil surface (Cochran, et al. 1967). This helps explain why such sites can have notoriously short frost-free periods and cold temperatures within the rooting zone. Douglas-fir (Pseudotsuga menziesii) is usually absent on soils with deep pumice (Simpson, 2007). In these cases, its role as an early-seral species appears to be filled by lodgepole pine (Pinus contorta) or Shasta red fir (Abies magnifica var. shastensis). Because water drains rapidly, herbaceous species are usually drought-tolerant when thickness of coarse ash and pumice exceeds two feet (Simpson, 2007).
Conifer forest is the dominant vegetation. Natural fire is moderately frequent, except infrequent in high-elevation forests associated with mountain hemlock (Tsuga mertensiana). Lodgepole pine is a widespread early-seral tree; mountain hemlock and Shasta red fir are relatively shade-tolerant. At lower elevations, ponderosa pine (Pinus ponderosa) and sugar pine (Pinus lambertiana) join lodgepole as fire-tolerant, early-seral trees; white fir (Abies concolor) is an associated shade-tolerant tree. Incense cedar (Calocedrus decurrens) also occurs. Wetlands support shrubby or herbaceous vegetation throughout this LRU.

Classification relationships

This ecological site group description is based on the ABMAS Moist Plant Association Group which includes the following Plant Associations (Simpson, 2007):

• Shasta red fir / pipsissewa
• Shasta red fir / giant chinquapin

Ecological site concept

This forested site occurs outside the pumice zone, in the warmer portion of the cryic soil temperature regime. Soil moisture regime is udic. Soils contain medial materials. Fine-earth textures are loamy. Shasta red fir is the dominant tree. Lodgepole pine is an important early-seral tree along with sugar pine and ponderosa pine. Douglas-fir (Pseudotsuga menziesii) is absent, perhaps due to cold air temperatures.

Associated sites

Similar sites

Table 1. Dominant plant species

Legacy ID

F003XF001OR