Natural Resources
Conservation Service
Ecological site AX002X02X003
Portland Basin Bogs and Fens
Last updated: 12/03/2024
Accessed: 12/21/2024
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): 002X–Willamette and Puget Sound Valleys
The Willamette and Puget Sound Valleys Major Land Resource Area (MLRA 2) is in western parts of Washington and Oregon. It occupies a forearc basin between the Coast Ranges and the Cascade Mountain volcanic arc. The northern part contains Pleistocene drift, outwash, and lacustrine and glaciomarine deposits associated with continental glaciers. The southern part contains Late Pleistocene deposits from glacial outburst floods (Missoula Floods).
Climate is mild and moist, and the growing season is long. Mean annual precipitation ranges from 20 to 60 inches, received mostly in fall, winter, and spring. Summers are dry. The soil temperature regime is mesic, and the soil moisture regimes are xeric and aquic.
Most sites in this MLRA can support forested vegetation, but some were maintained as prairie, savanna, or woodland through cultural burning prior to Euro-American settlement. Puget Sound has a moderating effect on temperatures, and humidity can be higher in the northern part of the MLRA. Douglas-fir (Pseudotsuga menziesii) is widespread throughout. Oregon white oak (Quercus garryana) is common on uplands in the south and on warm, exposed or droughty sites in the north. Pacific madrone grows in areas close to saltwater. Western hemlock (Tsuga heterophylla) is codominant with Douglas-fir in the north. Flood plains typically contain Brayshaw black cottonwood (Populus balsamifera ssp. trichocarpa) and red alder (Alnus rubra). Oregon ash (Fraxinus latifolia) is typical of forested wetlands in the south.
Forestry, urban development, and cultivated agriculture are currently the most extensive land uses (USDA, Agriculture Handbook 296, 2022).
LRU notes
The Portland Basin and Hills Land Resource Unit (LRU B) is in southwestern Washington and northwestern Oregon. The LRU extends north to the Cowlitz River and transitions to the Willamette Valley in the south. The Columbia River Gorge limits the eastern extent, and influence of tidewater at Cathlamet identifies the northwestern extent. Elevation ranges from sea level to about 2,000 feet. Major landforms include glaciofluvial terraces along the Columbia River, as well as residual hills and foothills surrounding the basin. Minor areas of Columbia River flood plain are present in Washington and more extensively in Oregon. Residual hills are composed primarily of Quaternary-Pliocene and Tertiary volcanic and sedimentary rocks. The lower-relief basin is composed primarily of sediment from catastrophic Quaternary glacial flooding from Glacial Lake Missoula.
The Columbia River splits this LRU between Oregon and Washington.
In Washington, mean annual precipitation ranges from 35 to 60 inches. Most falls as rain between October and May. The frost-free period ranges from 160 to 220 days. Locations near the Columbia River Gorge experience strong winds and infrequent ice storms with little winter snow. Average daily maximum temperatures in summer at Vancouver, Washington, are 1 to 3 degrees F warmer compared to Seattle or Olympia, Washington (Agricultural Climate Information System, 2007a, 2007b).
Oregon white oak and Douglas-fir are common north of the Columbia River in Washington. Western redcedar and western hemlock grow in areas of higher moisture, at higher elevations, or on protected aspects.
Ecological site concept
These plant communities typically grow in depressional areas that have an accumulation of undecomposed or partially decomposed organic matter and a high water table. These general kinds of bog and fen wetlands are distinguished by pH, nutrient availability, and hydrologic dynamics. Fens have groundwater within the rooting zone of vascular plants. Bogs have peat built up above the influence of groundwater. The vegetation in true bogs is limited by the water available from precipitation and is only in areas of high precipitation. The soils generally have a water table at or near the soil surface for much of the winter and spring, and the water table is often at or within a few feet of the soil surface for the remainder of the year. These soils are typically nutrient-poor and acidic.
This site can be compared to the Puget Lowlands Bog and Fens site in LRU A, which is similar but has lower summer temperatures and higher amounts of summer precipitation. The climate may be moister during the growing season in LRU A, leading to a shorter recovery between disturbances than in LRU B.
Associated sites
| AX002X02X007 |
Portland Basin Wet Forest |
|---|---|
| AX002X02X008 |
Portland Basin Riparian Forest |
Similar sites
| AX002X01X003 |
Puget Lowlands Peat Wetlands |
|---|---|
| R002XN603WA |
Bog or Fen |
Table 1. Dominant plant species
| Tree |
(1) Pinus contorta var. contorta |
|---|---|
| Shrub |
(1) Ledum groenlandicum |
| Herbaceous |
(1) Carex |
Legacy ID
R002XB003WA
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