Wetlands are covered with water during all or part of the year. Permanently wet habitats include backwater sloughs, oxbow lakes, and marshes, while seasonally wet habitats include seasonal ponds, vernal pools, and wet prairies. Wetland habitats are highly diverse and include the following different types:
- Alkaline wetlands occur in depressions in more arid areas and are intermittently flooded. An impermeable soil layer prevents water from percolating through the soil and concentrates salts in some areas. Soil salinity varies greatly by soil moisture and type and determines plant species. Plant species are tolerant of saline conditions due to the concentration of salts by water evaporation. Vegetation includes salt-tolerant grasses, rushes, sedges and shrubs such as black greasewood. Examples are found in the Klamath and Goose Lakes of the East Cascades ecoregion, and in the Northern Basin and Range ecoregion.
- Deciduous swamps and shrublands are located in depressions, around lakes or ponds or on river terraces. They generally flood seasonally with nutrient-rich waters and are dominated by woody vegetation including willows, hardhack, alder, red-osier dogwood, Pacific crab apple, and ash.
- Marshes (including emergent marshes) occur in depressions (ponds), fringes around lakes and along slow-flowing streams especially in valley bottoms. Marshes are seasonally or continually flooded and have water-adapted plants such as sedges, bulrush, spikesedges, rushes, cattails, and floating vegetation. Marshes can have mucky soils resulting in water with high mineral content and dominated by herbaceous species, often including wildflowers.
- Off-channel habitat (oxbow lakes, stable backwater sloughs, and flooded marshes) are created as rivers change course. In these areas, water moves slowly, providing quiet aquatic habitats.
- Playas, found in the Northern Basin and Range ecoregion, are sparsely vegetated (generally <10 percent plant cover) with grasses and are surrounded by a ring of shrubs. They are seasonally flooded and have highly saline soil. Plant species composition depends on soil salinity and moisture. Characteristic species include iodine bush, black greasewood, spiny hopsage, saltbush, alkali grass, wildrye and saltgrass.
- Seasonal ponds and vernal pools hold water during the winter and spring but typically dry up during the dry summer months. Vernal pools occur in complexes of networked depressions that are seasonally-filled with rainwater. They host a variety of species with unique adaptations.
- Wet meadows (including montane wet meadows) occur on gentle slopes near stream headwaters, in mountain valleys, bordering lakes and streams, near seeps, in large river valley bottoms, and in open wet depressions among montane forests. They are dominated by tufted hairgrass, sedges, reedgrass, spikesedge, rushes, and wildflowers. Montane wet meadows may have shallow surface water for part of the year, are associated with snowmelt, and are not typically subjected to disturbance events such as flooding
- Wet prairies occur in lowlands, especially in floodplains whereas wet meadows occur in depressions surrounded by forests and are associated with snowmelt. Wet prairies are dominated by grasses, sedges and wildflowers.
For more information on the Strategy Habitat: Wetlands, please see the Oregon Conservation Strategy (PDF file; 7.45 MB)
Excerpted with permission from Oregon Department of Fish and Wildlife. 2006. Oregon Conservation Strategy. Oregon Department of Fish and Wildlife, Salem, Oregon.