Physiognomy and Structure: The communities of this type are mostly forests, with woodlands occurring on some dry sites, and tree patches (islands) at upper elevations (near alpine tundra). Evergreen needle-leaved trees (conifers) dominate stands overall, although broad-leaved evergreens codominate in drier, southern areas. Broad-leaved deciduous trees occur in lower elevations, mostly in young stands. Most tree species are long-lived (500-1000 years and older) and stands tend to be tall, two- or multi-storied and composed of two or more species. Some stands are composed of very tall trees, 40-60 m or more in height (Picea sitchensis trees up to 90 m; Sequoia sempervirens trees up to 115 m), whereas other stands can be short, only 5-15 m tall. (e.g., high elevations near tree line). Shrub layers are often well-developed and composed of tall or short broad-leaved deciduous or evergreen shrubs. Dwarf-shrubs are common in and amongst tree patches at upper elevations. Forbs predominate in the herb layer, which is generally of low dominance, except on moist sites dominated by ferns. Bryophytes generally dominate on the forest floor. Young stands with a dense canopy often have little to no understory, except for some bryophytes.

Floristics: The forests and woodlands of this type are typically dominated by conifers (needle-leaved trees) or, in dry southern climates, by a mix of needle-leaved, broad-leaved evergreen, and broad-leaved deciduous trees. Deciduous broad-leaved trees are also found in younger stands in dry climates, and on recently disturbed sites throughout.

Much of the range of this division is characterized by Tsuga heterophylla, which occurs in lowland and low montane forests from Alaska to northern California. In Alaska and along the coast from British Columbia to southern Oregon, it commonly occurs with Picea sitchensis. These two species dominate forests of this division in Alaska and can occur with Callitropsis nootkatensis or Tsuga mertensiana. From northern British Columbia to southern Oregon, these two species, often with Thuja plicata, typically dominate the coastal band that is influenced by fog (also called "fog belt" or "hypermaritime"). In this zone they commonly occur with an understory dominated by Gaultheria shallon or Vaccinium ovatum. Picea sitchensis strongly dominates along outer coast stands influenced by salt spray. Further south, in California, Sequoia sempervirens occurs in this fog zone, often with Tsuga heterophylla (northern range) or Pseudotsuga menziesii.

Tsuga heterophylla occurs with Abies amabilis and Thuja plicata in moist climate forests that are just inland of the Tsuga heterophylla - Picea sitchensis forests along the coast of British Columbia, and at mid elevations along the windward slopes of coastal mountain ranges in Washington and Oregon. Callitropsis nootkatensis can codominate, particularly at higher elevations of these forests; Abies procera also occurs at higher elevations in the U.S. range. Common understory dominants are Blechnum spicant, Rhododendron macrophyllum, Rubus spectabilis, Vaccinium ovalifolium, and Rhytidiadelphus loreus. Small landslides often occur in areas of high precipitation and are initially covered by Alnus rubra.

Tsuga heterophylla occurs with Pseudotsuga menziesii and Thuja plicata in lowland and low montane forests of drier climates from southern British Columbia to southern Oregon. These forests are characterized by an understory that may include Acer circinatum, Achlys triphylla, Gaultheria shallon, Mahonia nervosa, Oxalis oregana, Polystichum munitum, Rhododendron macrophyllum, and Rubus spectabilis. Drier sites associated with these forests can be dominated by Pinus contorta, which may be either an early species or may persist on the driest sites. Younger mesic and moist forests often contain the broad-leaved deciduous trees Acer macrophyllum or Alnus viridis. Local climatic areas that are too dry for Tsuga heterophylla have conifer stands codominated by Pseudotsuga menziesii and Abies grandis, with Thuja plicata on moister sites. Dry sites in these areas may have scattered Arbutus menziesii or Quercus garryana with Pseudotsuga menziesii, or even stands dominated by Quercus garryana. The understory of these drier Pseudotsuga menziesii stands is similar to those with some Tsuga heterophylla, but with the following species being more prevalent: Corylus cornuta var. californica, Holodiscus discolor, Lonicera hispidula, and Symphoricarpos albus.

In coastal areas of southern Oregon and northern California, additional tree species occur. The lowest elevation stands are a mix of needle-leaved evergreen, broad-leaved evergreen, and broad-leaved deciduous trees, including Arbutus menziesii, Notholithocarpus densiflorus, Calocedrus decurrens, Pinus jeffreyi, Pinus lambertiana, Pinus ponderosa var. benthamiana, Pseudotsuga menziesii, Quercus chrysolepis, Quercus kelloggii, and Umbellularia californica. Abies concolor and Abies lowiana increases in abundance at higher elevations of these forests and forms mixed stands with Pseudotsuga menziesii at mid elevations. In California, these mid-elevation forests can also include Sequoiadendron giganteum. Other possible tree species are Abies bracteata, Chrysolepis chrysophylla, Picea breweriana, and Pseudotsuga macrocarpa.

High montane forests are characterized by Tsuga mertensiana, with Abies amabilis codominating in the central range (to extreme southeastern Alaska) and Abies magnifica (var. magnifica and var. shastensis) dominating in the southern range (southern Oregon and south). Several other tree species also occur in these high-elevation forests: Abies lasiocarpa and Callitropsis nootkatensis are found in the central and northern range, with Abies lasiocarpa in areas with a continental influence; Abies procera and Pinus monticola occur in the central range; Pinus albicaulis and Pinus contorta var. murrayana occur in the central and south. Abies lasiocarpa, Pinus albicaulis, Pinus contorta var. murrayana, and Tsuga mertensiana are the most frequent species at subalpine elevations. The understory of the central and northern forests is dominated by Vaccinium ovalifolium, often with Menziesia ferruginea, Elliottia pyroliflora, Rubus pedatus, Streptopus lanceolatus var. curvipes (= Streptopus roseus), Vaccinium membranaceum, and sometimes Rhododendron albiflorum. The southern forests have a drier climate and species such as Arctostaphylos nevadensis, Quercus sadleriana, Quercus vacciniifolia, Symphoricarpos oreophilus, and Xerophyllum tenax occur.

In some locales, the upper canopy may be dominated by non-native tree species such as Acer platanoides, Crataegus arborea, Ilex aquifolium, Ilex crenata, Pinus nigra, Pinus sylvestris, and Prunus padus, among others. Pinus nigra and Pinus sylvestris occur on stable sand dunes in Oregon; they were planted as a soil erosion measure.

Dynamics:  The predominant natural disturbance factor varies over this type, from areas with an historical preponderance of fire to those with essentially no fire where small-patch gap dynamics prevail. Areas with little to no fire occur in wetter climatic areas, mostly in the northern range of this type, but also some areas in the central range. These include forests dominated by Abies amabilis and Tsuga heterophylla, northern forests dominated by Picea sitchensis and Tsuga heterophylla, central and northern "fog belt" forests, and most high-montane and subalpine forests. These forests rarely burn; gaps due to death by insects or pathogens (primarily root-rots) and/or windthrow of individual trees or small patches are the predominant source of stand dynamics. Stands can be very old with individual trees 700 to over 1000 years in age. The gap dynamics in these old forests results in a multi-aged stand structure; however, unless growing in wind-protected conditions, windthrow and breakage tend to keep these forests from becoming or remaining very old. High-montane forests can also be impacted by snow avalanches that extend beyond what occurs normally within avalanche tracks.

Fire becomes an increasingly important factor of stand dynamics where drier climatic conditions exist in the more southern and submaritime ranges of this type, as well as dry microclimate pockets throughout the range. In drier stands, where fire did/does occur, the dominant natural (pre-European settlement) process included stand-replacing fires on average every 150-500 years. In these situations, where old-growth does exist, it is mostly "young old-growth" about 200-500 years in age. Natural-origin stands less than 200 years old are also common. Mixed-severity fires occur more frequently (about every 50-100 years) in the drier more submaritime and often southern parts of this division. Pseudotsuga menziesii is usually prevalent in areas influenced by fire.

In the driest climatic areas, stand-maintaining surface fires, both aboriginal and lightning-caused, were more frequent (perhaps every 50-100 years) and likely maintained a moderately open overstory as well as favoring fire-adapted species. For example, the thick bark of Pseudotsuga menziesii allows it to survive surface fires, and Arbutus menziesii can generate from stump sprouts following fire. Due to fire suppression, the majority of these forests now exist with closed canopies. In many cases, Abies grandis, Tsuga heterophylla, and other fire-sensitive, shade-tolerant species dominate forests on sites once dominated by Pseudotsuga menziesii and Pinus ponderosa, which were formerly maintained by wildfire. Fire suppression has tended to result in increasing abundance of Arbutus menziesii, Notholithocarpus densiflorus, and Umbellularia californica. Sequoia sempervirens stands historically had surface fires that exposed mineral soil necessary for redwood seed germination.

Small landslides are frequent in wetter climates and are initially colonized by Alnus rubra. These small patches are evident on the landscape.

Human disturbances have altered stand structure, species composition and landscape pattern of forests of this type. Logging is prevalent, and areas once dominated by old stands of Pseudotsuga menziesii or Sequoia sempervirens have been logged for over a century. It is estimated that 95% or more of the original old-growth Sequoia sempervirens trees have been cut down. Landscapes in areas of forest harvesting have a reduced proportion of old stands and an increased component of broad-leaved deciduous species such as Acer macrophyllum or Alnus rubra. These seral forests can persist (>200 years) and remain as mixed deciduous-conifer forests.

The introduction of Sitka black-tailed deer to Haida Gwaii has drastically altered the understory biomass on forests of the islands; due to lack of predators, the deer have proliferated.