Invalid Unit Specified
D193 Populus balsamifera ssp. trichocarpa - Thuja plicata - Callitropsis nootkatensis Flooded & Swamp Forest Division

The U.S. National
Vegetation Classification
Type Concept Sentence: This division is comprised of forested wetlands of temperate maritime climates from southern Alaska to northern California, including riparian forests, rich swamps, and poor peat swamps (dominated by broad-leaved deciduous and needle-leaved trees.
Collapse All::Expand All
Common (Translated Scientific) Name: Black Cottonwood - Western Red-cedar - Alaska-cedar Flooded & Swamp Forest Division
Colloquial Name: Vancouverian Flooded & Swamp Forest
Hierarchy Level: Division
Type Concept: This division consists of forests and woodlands of wetland and riparian areas of temperate maritime climates from southern Alaska to northern California. It includes lowland and montane riparian forests, forested mineral-soil swamps, and poor swamps ("bog forests"). In lowland riparian forests, broadleaf dominant species are Acer macrophyllum, Alnus rubra, Populus balsamifera ssp. trichocarpa, Salix lucida ssp. lasiandra, and/or Fraxinus latifolia (in southern part of range), and conifer-dominated species are Abies grandis, Picea sitchensis, or Thuja plicata. Montane riparian areas are often conifer-dominated by such tree species as Abies amabilis, Abies concolor, Abies magnifica, Pinus contorta var. murrayana, Populus tremuloides, and/or Tsuga mertensiana. Montane riparian shrub species include Alnus viridis ssp. sinuata, Ribes bracteosum, and Rubus spectabilis. Treed swamps are small in size and indicative of poorly-drained, saturated to seasonally flooded, mostly mineral soil areas, often in a mosaic of moving and stagnant water and are dominated by any one or a number of conifer species (Callitropsis nootkatensis, Picea sitchensis, Pinus contorta, Tsuga heterophylla, Tsuga mertensiana) and broad-leaved deciduous species (Alnus rubra, Betula papyrifera, Fraxinus latifolia). Poor swamps ("bog forests") are common in southeastern Alaska and central British Columbia, less so farther south, and occur on poorly-drained peat soils. These are codominated by several conifer species, including Callitropsis nootkatensis, Picea sitchensis, Pinus contorta var. contorta, Tsuga heterophylla, or Tsuga mertensiana. The tree canopy is moderately open and of poor productivity; there is a high shrub cover composed of conifers, Gaultheria shallon and Vaccinium ovalifolium.
Diagnostic Characteristics: Treed wetlands in a maritime, temperate climate influenced by minerotrophic groundwater, either on mineral or organic soils. The vegetation is dominated by broad-leaved deciduous or needle-leaved trees, over 10% cover, including Abies amabilis, Acer macrophyllum, Alnus rubra, Callitropsis nootkatensis, Fraxinus latifolia, Picea sitchensis, Pinus contorta var. contorta, Populus balsamifera ssp. trichocarpa, Salix lucida ssp. lasiandra, Tsuga heterophylla, Thuja plicata, or Tsuga mertensiana. Strong diagnostic indicators in the understory are Carex obnupta, Coptis aspleniifolia, Equisetum telmateia, Maianthemum dilatatum, Ribes bracteosum, and Rubus spectabilis. Moderate diagnostic indicators include Carex deweyana, Equisetum arvense, Elliottia pyroliflora, Ledum groenlandicum, Lysichiton americanus, Oplopanax horridus, Sambucus racemosa, and Tiarella trifoliata.
Rationale for Nominal Species or Physiognomic Features: Populus balsamifera ssp. trichocarpa was selected to cover riparian situations over the range, Thuja plicata for low-elevation swamps, and Callitropsis nootkatensis for higher elevation and northern swamps.
Classification Comments: Most of the tree species are characteristic of temperate maritime climates and can occur on upland and wetland site conditions. The understory species associated with the wetland sites differ from those of uplands, as do the soil conditions. Although some species can occur in both moist upland and in riparian or swamps sites, the full complement of species on these site conditions differ. Populus balsamifera ssp. trichocarpa is mostly restricted to riparian and wetland sites within this division, but can also occur in riparian and swamp communities of Rocky Mountain-Great Basin Montane Flooded & Swamp Forest Division (D195); however, the understory floristics differ in cottonwood communities between these two divisions. Higher benches in riparian areas may be sufficiently dry to be placed in the upland Vancouverian Forest & Woodland Division (D192).

Low-productivity poor swamps ("bog forests") in this Pacific Coast division are similar to treed bogs, which are placed in North American Bog & Fen Division (D029), North Pacific Bog & Fen Macrogroup (M063). However, the "bog forests" are more productive and have less cover of key bog indicators such as Ledum groenlandicum, Myrica gale, Trichophorum cespitosum, and Sphagnum spp. The most common peatmoss of poor swamps is Sphagnum girgensohnii. MacKenzie and Moran (2004) use the term Bog to include both ombrotrophic bogs and weakly minerotrophic poor swamps. We place the more productive poor swamps here, recognizing that they may be difficult to distinguish from treed bogs. According to Mackenzie and Moran (2004) poor swamps are more commonly >10 m height with >10% tree cover, and have at least some minerotrophic floristic indicators.
Similar NVC Types:
D029 North American Bog & Fen, note: "includes treed and open bogs and fens. In treed bogs, the trees are of lower stature and seldom reach 10 m."
D016 North American Boreal Flooded & Swamp Forest, note:
D013 Western North American Interior Flooded Forest, note: "is composed of riparian, swamp and bog/fen forests south of D193 and D195."
D192 Vancouverian Forest & Woodland, note: includes upland forests within the range of D193. Moderately well-drained seepage forest are included in D192.
D195 Rocky Mountain-Great Basin Montane Flooded & Swamp Forest, note: "includes riparian, swamp and bog/fen forests from temperate continental climates of western North America directly to the east of D193."
Physiognomy and Structure: Closed- to open-canopy forests of cold-deciduous trees, evergreen trees, or a mix of deciduous and evergreen trees, often with deciduous or evergreen shrub undergrowth that includes tree regeneration and/or an herbaceous undergrowth layer. Mosses are often abundant, except on sites with frequent flooding or with a predominately deciduous overstory. Poor swamps may have stunted trees, but typically are >10 m in height with >10% cover (Mackenzie and Moran 2004).
Floristics: Riparian trees occurring throughout most of the range are Alnus rubra, Picea sitchensis, Populus balsamifera ssp. trichocarpa, Thuja plicata, and Tsuga heterophylla. Additional trees in southern areas include Acer macrophyllum, Salix lucida ssp. lasiandra, Fraxinus latifolia, and Abies grandis. Populus balsamifera is much less common on the islands of southeastern Alaska and off British Columbia due to a lack of larger floodplains. Dominant species of higher montane riparian areas include Abies amabilis, Abies concolor, Abies magnifica, Picea engelmannii, Pinus contorta var. murrayana, Tsuga mertensiana, and, more rarely, Populus tremuloides. Key understory diagnostics include Cornus sericea, Maianthemum dilatatum, Oplopanax horridus, Ribes bracteosum and Rubus spectabilis. Swamp tree species may include Alnus rubra, Betula papyrifera, Callitropsis nootkatensis, Fraxinus latifolia, Picea sitchensis, Pinus contorta var. contorta, Thuja plicata, Tsuga heterophylla, and/or Tsuga mertensiana. Shrub species include Cornus sericea, Elliottia pyroliflora, Gaultheria shallon (southern portion of the Alaska distribution only), Ledum groenlandicum, Oplopanax horridus, Ribes bracteosum, Rubus spectabilis, Spiraea douglasii, Vaccinium ovalifolium, and/or Vaccinium uliginosum. Mosses include various species of the Mniaceae. Trees of poor swamps ("bog forests") are codominated by several species, including Callitropsis nootkatensis, Pinus contorta var. contorta, Tsuga heterophylla, or Tsuga mertensiana, and, south of Alaska, also Thuja plicata. Conifers dominate the shrub layer along with Gaultheria shallon and Vaccinium ovalifolium. Coptis aspleniifolia is a characteristic herb; other herbs include Cornus unalaschkensis and Blechnum spicant. Sphagnum girgensohnii is characteristic on the forest floor, along with Rhytidiadelphus triquetrus and Hylocomium splendens.
Dynamics: Riparian forests are subject to the erosional dynamics of rivers occurring in areas of high precipitation and/or snowmelt, including erosion of banks and upstream benches, and deposition on lower benches and reaches. Some rivers are characterized by broad shifting alluvial riverbanks. Succession on benches initiates with regeneration of willow, black cottonwood or red alder seedlings, with eventual regeneration of conifers. The older or "high" benches are conifer-dominated and are rarely flooded; they are more prone to erosional events. The youngest or "low" benches are continually being formed by deposition; they are composed of young willow, red alder or black cottonwood stands, and are often flooded and strongly influenced by subsurface seepage. The "mid" benches are generally characterized by mixed broad-leaved deciduous and conifer stands and are less frequently flooded and less influenced by subsurface seepage.

Across the forests of this division, windthrow is a key disturbance factor that can result in either single-tree gaps or multi-tree gaps that disturb larger forest areas. Fire is not a significant disturbance factor. In the hypermaritime coastal climates, paludification is a prevailing process and bog formation occurs on many slopes as well as on level areas. Paludification is slowed on steeper terrain where soil drainage is better and disturbance by slope failure or windthrow is frequent.
Environmental Description: Forests of this division occur on wetland or riparian areas with permanently saturated soils or seasonal water table fluctuations. They occur at low and high elevations throughout the coastal regions of the Pacific Northwest, ranging from sea level to as high as 3300 m (10,000 feet).

Climate: This division occurs within a temperate maritime climate.

Soils/substrate: Soils range from thin, to poorly-developed and coarse to deep peat. Riparian sites may have frequent flooding, shifting channels, and significant sediment deposition. Poor swamps ("bog forests") are poorly-drained with slow-moving groundwater and on deep organic or gleysolic soils.

Biogeography: The species composition of these communities is reasonably uniform over the range. Abies amabilis and Thuja plicata do not occur in most of the Alaskan part of the range. Abies amabilis is absent from the islands of Haida Gwaii. Abies concolor, Abies grandis, Abies magnifica, and Fraxinus latifolia have a southern distribution. Species of higher elevations include Abies amabilis, Abies magnifica, and Tsuga mertensiana.
Geographic Range: This division occurs at low and high elevations throughout the coastal regions of the Pacific Northwest from northern California north through British Columbia, Vancouver Island and Haida Gwaii to along the coast of the Gulf of Alaska, including central and southeastern Alaska.
Nations: CA, US
States/Provinces: AK, BC, CA, OR, WA
US Forest Service Ecoregions (2007)
Domain Name:
Division Name:
Province Name:
Province Code:     Occurrence Status:
Section Name:
Section Code:     Occurrence Status:
Omernik Ecoregions:
Plot Analysis Summary:
Confidence Level: Moderate
Confidence Level Comments:
Grank: GNR
Name:Database Code:Classification Code:
Class 1 Forest & Woodland C01 1
Subclass 1.B Temperate & Boreal Forest & Woodland S15 1.B
Formation 1.B.3 Temperate Flooded & Swamp Forest F026 1.B.3
Division 1.B.3.Ng Vancouverian Flooded & Swamp Forest D193 1.B.3.Ng
Macrogroup M035 Vancouverian Flooded & Swamp Forest M035 1.B.3.Ng.1
Concept Lineage: D012 (former 1.C.3.Nc) split into 2 new types (D193 & D195).
Obsolete Names:
Populus balsamifera ssp. trichocarpa - Thuja plicata - Chamaecyparis nootkatensis Flooded & Swamp Forest Division
Obsolete Parents:
Synonomy: < Fl, Ws (MacKenzie and Moran 2004) [Forested swamps, and flood ecosystems are a subset of the vegetation presented for British Columbia.]
> Forest and woodland wetlands (Christy 2004) [Forested wetlands are one section of wetland vegetation of northwestern Oregon.]
> Tree-dominated wetlands (Kunze 1994) [Forested wetlands are one section of wetland vegetation of western Washington.]
> low-elevation riparian vegetation of Olympic Experimental State Forest (Chappell 1999) [riparian vegetation for one area of Washington state.]
Concept Author(s): D. Faber-Langendoen et al. (2015)
Author of Description: D. Meidinger and G. Kittel
Acknowledgements: T. Boucher, C. Chappell, M.S. Reid, and D. Faber-Langendoen
Version Date: 09Dec2015
  • Chappell, C. B. 1999. Ecological classification of low-elevation riparian vegetation on the Olympic Experimental State Forest: A first approximation. Unpublished progress report. Washing Natural Heritage Program, Washington Department of Natural Resources, Olympia. 43 pp.
  • Christy, J. A. 2004. Native freshwater wetland plant associations of northwestern Oregon. Oregon Natural Heritage Information Center, Oregon State University, Portland, OR.
  • 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]
  • Kunze, L. M. 1994. Preliminary classification of native, low elevation, freshwater wetland vegetation in western Washington. Washington State Department of Natural Resources, Natural Heritage Program. 120 pp.
  • MacKenzie, W. H., and J. R. Moran. 2004. Wetlands of British Columbia: A guide to identification. Land Management Handbook No. 52. Research Branch, British Columbia Ministry of Forests and Lands, Victoria, BC. 287 pp.