Common (Translated Scientific) Name: Douglas-fir - Western Hemlock - Mountain Hemlock Vancouverian Forest & Woodland Division
Colloquial Name: Vancouverian Forest & Woodland
Hierarchy Level: Division
Type Concept: This division includes forests and woodlands of the lowland, montane and subalpine zones of maritime temperate climates of western North America, ranging from the Gulf of Alaska to California and south in high elevations of the mountains of Baja California, Mexico. Evergreen needle-leaved trees (conifers) dominate stands overall although broad-leaved evergreens codominate in drier climate areas in the southern range. Strong diagnostic conifers include Abies amabilis, Callitropsis nootkatensis, Picea sitchensis, Pinus contorta var. contorta, Pseudotsuga menziesii var. menziesii, and Tsuga mertensiana. Moderate diagnostic conifers are Abies grandis, Abies lowiana, Abies magnifica (var. magnifica, var. shastensis), Abies procera, Calocedrus decurrens, Chamaecyparis lawsoniana, Pinus jeffreyi, Pinus lambertiana, Pinus ponderosa var. benthamiana, Sequoia sempervirens, Sequoiadendron giganteum, Thuja plicata, and Tsuga heterophylla. The broadleaf evergreen trees Arbutus menziesii, Notholithocarpus densiflorus, Quercus chrysolepis, and Umbellularia californica, and the broad-leaved deciduous trees Acer macrophyllum, Quercus garryana, and Quercus kelloggii are moderate diagnostic species. Alnus rubra, a broadleaf deciduous species, is a strong diagnostic. Most tree species are long-lived 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. Understory shrub layers are often well-developed, whereas forbs are generally of low dominance, unless dominated by ferns. Bryophytes are often of high cover. Strong diagnostic understory species include Acer circinatum, Achlys triphylla, Blechnum spicant, Elliottia pyroliflora, Gaultheria shallon, Mahonia nervosa, Oxalis oregana, Polystichum munitum, Rhododendron macrophyllum, Rubus spectabilis, Vaccinium alaskaense, Vaccinium parvifolium, Vaccinium ovatum, and Rhytidiadelphus loreus.
Although influenced by a maritime climate, the major types of forests and woodlands vary in response to degree of maritime influence, temperature regimes as impacted by elevation and latitude, and precipitation regimes. Precipitation can be as low as 50 cm (20 inches) in the extreme rainshadow areas and over 400 cm (1000 inches) in the wetter mountains. Lower elevations mostly receive 90-380 cm (35-150 inches) falling predominantly as winter rain. Hypermaritime areas receive additional moisture by fog drip. Winter snowfall ranges from absent, to rare to regular, with the highest amount and duration occurring in higher elevations and northern areas. In drier areas and warm exposures, particularly in the southern range, summer drought can be significant. These forests and woodlands occur on a variety of upland soils including dry to moist upper, mid- and toeslopes, valley floors and side terraces, and stabilized coastal sand dunes. Some soils are influenced by salt spray. Bedrock geology includes volcanic, intrusive, metamorphic, sedimentary and ultramafic rocks.
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. 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. Logging has altered the stand structure, species composition, and landscape pattern of forests of this type.
Diagnostic Characteristics: Maritime-influenced conifer and mixed broadleaf evergreen forests and woodlands of upland areas bordering the Pacific Coast and western mountain slopes from Alaska to Baja California. Strong and moderate diagnostic tree species are Abies amabilis, Abies concolor, Abies grandis, Abies lowiana, Abies magnifica, Abies procera, Acer macrophyllum, Alnus rubra, Arbutus menziesii, Calocedrus decurrens, Callitropsis nootkatensis, Chamaecyparis lawsoniana, Picea sitchensis, Pinus contorta var. contorta, Pinus jeffreyi, Pinus lambertiana, Pinus ponderosa var. benthamiana, Pseudotsuga menziesii var. menziesii, Sequoia sempervirens, Sequoiadendron giganteum, Thuja plicata, Tsuga heterophylla, and Tsuga mertensiana.
Rationale for Nominal Species or Physiognomic Features: Pseudotsuga menziesii is common in the southern distribution at lower elevations; Tsuga heterophylla in central and northern areas at low to mid elevations, and Tsuga mertensiana at high-montane elevations through most of the range.
Classification Comments: Over much of the eastern range of this, it abuts 1.B.2.Nb Rocky Mountain Forest & Woodland Division (D194). There is some overlap in tree species between the two divisions, such as Abies grandis, Pinus contorta, Pinus ponderosa, Pseudotsuga menziesii, Thuja plicata, and Tsuga heterophylla (different varieties for Pinus contorta, Pinus ponderosa, and Pseudotsuga menziesii) but numerous tree and understory species are helpful in distinguishing the two. Understory species such as Gaultheria shallon, Rubus spectabilis, Mahonia nervosa, Polystichum munitum, and Rhytidiadelphus loreus are found in D192, whereas Vaccinium membranaceum, Vaccinium scoparium, Calamagrostis rubescens, Xerophyllum tenax, and Pleurozium schreberi predominate in D194.
In Alaska, this division transitions to 1.B.4.Na North American Boreal Forest & Woodland Division (D014). That division includes the "subboreal" component where Picea x lutzii and occasional Tsuga mertensiana are found, along with Picea glauca and Picea mariana [see Southern Alaskan Boreal Mesic Forest Group (G627) in Alaskan-Yukon North American Boreal Forest Macrogroup (M156)]. The gradient may be too rapid in Alaska to have reasonable expression of a distinct subboreal component at the group or higher level.
The name Pinus ponderosa var. benthamiana is used in this description for the Pacific coastal subtaxon. A recent paper from the USDA Forest Service (Callaham 2013) proposes that the taxon be named Pinus ponderosa ssp. critchfieldiana. Abies lowiana is treated as a specific rank in USDA Plants and Flora of North America (FNA Editorial Committee 1993). It seems that both species occur in this division.
Similar NVC Types:
D007 Californian Forest & Woodland, note: "includes warmer climate forests, woodlands and savannas dominated by oak and conifer species that occur south of D192."
D014 North American Boreal Forest & Woodland, note: "includes cold, continental climate forests and woodlands that abut D192 in Alaska."
D193 Vancouverian Flooded & Swamp Forest, note: includes floodplain and swamp forests over the range of D192.
D194 Rocky Mountain Forest & Woodland, note: "includes predominately conifer forests and woodlands of temperate continental climate areas that occur to the east of the D192. To the north, in northern British Columbia, D194 forests are a narrow band between coastal forests of D192 and boreal forests of D014."
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.
Environmental Description: Forests and woodlands of this type occur on upland sites of cool-temperate, maritime-influenced regions of western North America. Elevations range from sea level to the alpine tundra treeline, which occurs at about 900-1350 m (3000-4500 feet) in the northern range (the higher elevations occur more inland where the snowpack is not as deep and heavy), and up to 3670 m (12,000 feet) in the south.
Climate: The climate is cool-temperate and maritime, ranging from hypermaritime, along the outer coast, to submaritime on the eastern slopes of the major coastal mountain ranges, i.e., Coast, Cascade and Sierra Nevada. Temperature regimes vary considerably from south to north, low to high elevation, and distance from the coast, but overall, winters are milder and summers generally cooler than forest types to the east. Mean annual precipitation and amount of snow also vary considerably along the same gradients as temperature. Precipitation can be as low as 50 cm (20 inches) in the extreme rainshadow areas and over 400 cm (1000 inches) in the wetter mountains. Lower elevations mostly receive 90-380 cm (35-150 inches) falling predominantly as winter rain. Hypermaritime areas receive additional moisture by fog drip. Winter snowfall ranges from absent, to rare to regular, with the highest amount and duration occurring in higher elevations and northern areas. High-montane areas in the northern range can have a heavy (high moisture content) snow cover for 5-9 months. In drier areas and warm exposures, particularly in the southern range, summer drought can be significant.
Soils/substrate: These forests and woodlands occur on a variety of upland soils, including dry to moist upper, mid- and toeslopes, valley floors and side terraces, and stabilized coastal sand dunes. Soils range from dry to subirrigated, and although generally deep and fine- to moderately coarse-textured, they can also be on ridges and rocky slopes, with shallow and coarse-textured, rocky substrates. Slopes can be gentle to extremely steep. Some soils are influenced by salt spray. Bedrock geology includes volcanic, intrusive, metamorphic, sedimentary and ultramafic rocks.
Biogeography: The expression of the major types of forests and woodlands of this division are in response to climatic gradients of continentality (hypermaritime to submaritime), temperature (elevation and latitude), and precipitation, as well as differences in the flora from north to south. The Vancouverian flora from Alaska to the mid-coast of British Columbia, extending south to mid Oregon in the wetter climates and higher elevations, is reasonably uniform in tree species and understory. Tsuga heterophylla, Tsuga mertensiana, Callitropsis nootkatensis, and Picea sitchensis range throughout; Abies amabilis and Thuja plicata do not occur in most of Alaska but otherwise occur, except that Abies amabilis is absent from the islands of Haida Gwaii.
The lower elevation, drier, rainshadow climates from southern British Columbia to mid Oregon and California also have a reasonably uniform flora, composed of species that tolerate warmer and drier conditions. Pseudotsuga menziesii is prevalent in this region, which also includes Arbutus menziesii, Quercus garryana, and Abies grandis, in addition to the wide-ranging Tsuga heterophylla.
The flora from southern Oregon into the forested regions of California is broadly uniform, comprised of wide-ranging species such as Abies concolor, Abies lowiana, Abies magnifica, Calocedrus decurrens, Notholithocarpus densiflorus, Pinus jeffreyi, Pinus lambertiana, Pinus ponderosa var. benthamiana, Pseudotsuga menziesii, Quercus chrysolepis, Quercus kelloggii, and Umbellularia californica. A few species have restricted ranges, e.g., Abies bracteata, Chrysolepis chrysophylla, Picea breweriana, Pinus coulteri, Pseudotsuga macrocarpa, Sequoia sempervirens, and Sequoiadendron giganteum.
Geographic Range: This division ranges along the coast, including coastal islands, and east into the coastal mountain ranges (Coast, Cascade, Sierra Nevada) from the Gulf of Alaska south to California. It also occurs south through the maritime lowlands of western California, and at high elevations, south through the Peninsula and Transverse ranges to Baja California, Mexico.
Nations: CA, MX, US
States/Provinces: AK, BC, CA, MXBC, NV, OR, WA
|US Forest Service Ecoregions (2007)|
Confidence Level: High
Confidence Level Comments:
Concept Lineage: D009 (former 1.C.2.Nb) split into 2 new divisions (D192 & D194).
Synonomy: < Pacific Northwest Forests (Franklin and Halpern 2000) [Franklin and Halpern describe forests of Oregon northward.]
< Temperate and Boreal Rainforests of the Pacific Northwest (DellaSala et al. 2010) [DellaSala et al. include cedar - hemlock forests of temperate continental climates (called "boreal").]
Concept Author(s): J.F. Franklin and C.B. Halpern (2000)
Author of Description: D. Meidinger
Acknowledgements: G. Kittel, M.S. Reid, D. Faber-Langendoen
Version Date: 30Oct2015
- Callaham, R. Z. 2013. Pinus ponderosa: A taxonomic review with five subspecies in the United States. Research Paper PSW-RP-264. USDA Forest Service, Pacific Southwest Research Station, Albany, CA. 52 pp.
- DellaSala, D .A., F. Moola, P. Alaback, P. C. Paquet, J. W. Schoen, and R. Noss. 2010. Temperate and boreal rainforests of the Pacific Coast of North America. Chapter 2 in: D. A. DellaSala, editor. Temperate and Boreal Rainforests of the World: Ecology and Conservation. Island Press, Washington, DC. ISBN: 9781597266758. 336 pp.
- Faber-Langendoen, D., J. Drake, S. Gawler, M. Hall, C. Josse, G. Kittel, S. Menard, C. Nordman, M. Pyne, M. Reid, L. Sneddon, K. Schulz, J. Teague, M. Russo, K. Snow, and P. Comer, editors. 2010-2019a. Divisions, Macrogroups and Groups for the Revised U.S. National Vegetation Classification. NatureServe, Arlington, VA. plus appendices. [in preparation]
- FNA Editorial Committee [Flora of North America Editorial Committee], editors. 1993. Flora of North America, north of Mexico. Volume 2. Pteridophytes and gymnosperms. Oxford University Press, New York. xvi plus 475 pp.
- Franklin, J. F., and C. B. Halpern. 2000. Pacific Northwest forests. Chapter 5 in: M. G. Barbour and W. D. Billings, editors. North American terrestrial vegetation. Cambridge University Press, New York.
- Orians, G., and D J. Schoen, editors. 2013. North Pacific temperate rainforests. University of Washington Press, Seattle. ISBN: 9780295992617. 416 pp.