North Pacific Mesic Western Hemlock-Silver Fir Forest
This forested system occurs only in the Pacific Northwest mountains entirely west of the Cascade Crest from coastal British Columbia to Washington, and probably occurs in southeastern Alaska. It generally occurs in an elevational band between Pseudotsuga menziesii - Tsuga heterophylla or hypermaritime zone forests and Tsuga mertensiana forests. It dominates mid-montane maritime climatic zones on the windward side of Vancouver Island, the Olympic Peninsula, and the wettest portions of the North Cascades in Washington (north of Snoqualmie River). A somewhat variable winter snowpack that typically lasts for 2-6 months is characteristic. The climatic zone within which it occurs is sometimes referred to as the "rain-on-snow" zone because of the common occurrence of major winter rainfall on an established snowpack. Tsuga heterophylla and/or Abies amabilis dominate the canopy of late-seral stands, and Chamaecyparis nootkatensis can be codominant, especially at higher elevations. Thuja plicata is also common and sometimes codominates in British Columbia. In Alaska, Abies amabilis occurs in nearly pure stands and in mixture with Picea sitchensis and Tsuga heterophylla. Pseudotsuga menziesii is relatively rare to absent in this system, as opposed to the similar but drier North Pacific Dry-Mesic Silver Fir-Western Hemlock-Douglas-fir Forest (CES204.098). The major understory dominant species is Vaccinium ovalifolium. Understory species that help distinguish this system from the drier silver fir system (they are much more common here) include Oxalis oregana, Blechnum spicant, and Rubus pedatus. Windthrow is a common small-scale disturbance in this system, and gap creation and succession are important processes.