Pacific Northwest Shrub Swamp

Swamps vegetated by shrublands occur throughout the Pacific Northwest Coast, from Cook Inlet and Prince William Sound, Alaska, to the southern coast of Oregon. These are deciduous broadleaf tall shrublands that are located in depressions, around lakes or ponds, or river terraces where water tables fluctuate seasonally (mostly seasonally flooded regime), in areas that receive nutrient-rich waters. These depressions are poorly drained with fine-textured organic, muck or mineral soils and standing water common throughout the growing season. Alnus viridis ssp. sinuata often dominates the shrub layer, but many Salix species may also occur. The shrub layer can have many dead stems. However, various species of Salix, Spiraea douglasii, Malus fusca, Cornus sericea, Alnus incana ssp. tenuifolia (= Alnus tenuifolia), Alnus viridis ssp. crispa (= Alnus crispa), and/or Alnus viridis ssp. sinuata (= Alnus sinuata) can be the major dominants. They may occur in mosaics with marshes or forested swamps, being on average more wet than forested swamps and more dry than marshes. However, it is also frequent for them to dominate entire wetland systems. Hardwood-dominated stands (especially Fraxinus latifolia) may be considered a shrub swamp when they are not surrounded by conifer forests but do not occur in Alaska. Typical landscape for the Fraxinus latifolia stands were very often formerly dominated by prairies and now by agriculture. Wetland species, including Carex aquatilis var. dives (= Carex sitchensis), Carex utriculata, Equisetum fluviatile, and Lysichiton americanus, dominate the understory. On some sites, Sphagnum spp. are common in the understory (Stikine, Yakutat Forelands, Copper River Delta).

This system occurs throughout the Pacific Northwest Coast, from Cook Inlet Basin and Prince William Sound, Alaska, to the southern coast of Oregon.