Pacific Northwest Mountain Hemlock Forest

This forested ecological system occurs throughout the mountains of the North Pacific, from the southern Cascades of Oregon north to southwestern British Columbia. It is the predominant forest of subalpine elevations in the coastal mountains of British Columbia, western Washington and western Oregon. It also occurs on mountain slopes on the outer coastal islands of British Columbia. It lies between the Western Hemlock, Pacific Silver Fir, or Shasta Red Fir zones and the Subalpine Parkland or Alpine Tundra Zone, at elevations ranging from 300 to 2300 m (1000-7500 feet). The lower and upper elevational limits decrease from south to north and from east to west. The climate is generally characterized by short, cool summers, rainy autumns and long, cool, wet winters with heavy snow cover for 5-9 months. The heavy snowpack is ubiquitous, but at least in southern Oregon and perhaps the eastern Cascades, summer drought is more significant. Fire is very rare or absent across the majority of the range of the system. Tsuga mertensiana is one of the dominant tree species throughout, and Abies amabilis becomes an important associated species in the southern portion of the range (British Columbia, Washington, and northwestern Oregon). Tsuga heterophylla often occurs at lower elevations in this system but is much less abundant than Tsuga mertensiana. Callitropsis nootkatensis occurs in the more coastal portions, while Abies lasiocarpa is found inland and becomes increasingly common near the transition to the Subalpine Fir-Engelmann Spruce Zone in the Cascades and British Columbia. On the leeward side of the Cascades, this is usually a dense canopy composed of Abies lasiocarpa and Tsuga mertensiana, with some Picea engelmannii or Abies amabilis. In the Cascades of central to southern Oregon, Abies magnifica var. shastensis is typically present and often codominant. Picea sitchensis and Thuja plicata are occasionally present. Deciduous trees are rare. Common understory species include Vaccinium ovalifolium, Menziesia ferruginea, Elliottia pyroliflora, and Blechnum spicant. Parklands (open woodlands or sparse trees with dwarf-shrub or herbaceous vegetation) are not part of this system but of North Pacific Maritime Mesic Subalpine Parkland (CES204.837) or Alaskan Pacific Maritime Subalpine Mountain Hemlock Woodland (CES204.143).

Tsuga mertensiana is one of the dominant tree species throughout, and Abies amabilis becomes an important associated species in the southern portion of the range (British Columbia, Washington, and northwestern Oregon). Tsuga heterophylla often occurs at lower elevations in this system but is much less abundant than Tsuga mertensiana. Callitropsis nootkatensis (= Chamaecyparis nootkatensis) occurs in the more coastal portions, while Abies lasiocarpa is found inland and becomes increasingly common near the transition to the Subalpine Fir-Engelmann Spruce Zone in the Cascades and British Columbia. On the leeward side of the Cascades, this is usually a dense canopy composed of Abies lasiocarpa and Tsuga mertensiana, with some Picea engelmannii or Abies amabilis. In the Cascades of central to southern Oregon, Abies magnifica var. shastensis (= Abies x shastensis) is typically present and often codominant. Picea sitchensis and Thuja plicata are occasionally present. Deciduous trees are rare. Common understory species include Vaccinium ovalifolium, Menziesia ferruginea, Elliottia pyroliflora, and Blechnum spicant.

In the more summer-dry climatic areas (Cascades), occasional high-severity fires occur, with return intervals of 400-600 years (J. Kertis pers. comm. 2006, K. Kopper pers. comm. 2006). On drier sites, Abies lasiocarpa and Pinus contorta can be the first forests to develop after stand-replacing fire. These early-seral stages, with lodgepole pine dominant in the upper canopy, could be classified and mapped as Rocky Mountain Lodgepole Pine Forest (CES306.820) but should be considered part of this system if other tree species listed above are present, as it will succeed as a mixed pine type, then mountain hemlock becomes characteristic. Landfire VDDT models: R#ABAMup.

This system occurs from coastal British Columbia to the southern Cascades of Oregon.