Invalid Unit Specified
Division Detail Report: D193
Populus balsamifera ssp. trichocarpa - Thuja plicata - Chamaecyparis nootkatensis Flooded & Swamp Forest Division

The U.S. National
Vegetation Classification
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.
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Translated Name:Black Cottonwood - Western Red-cedar - Alaska-cedar Flooded & Swamp Forest Division
Colloquial Name:Vancouverian Flooded & Swamp Forest
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 (Chamaecyparis 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 Chamaecyparis nootkatensis (= 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.
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, Chamaecyparis 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 pyroliflorus, Ledum groenlandicum, Lysichiton americanus, Oplopanax horridus, Sambucus racemosa, and Tiarella trifoliata.
Populus balsamifera ssp. trichocarpa was selected to cover riparian situations over the range, Thuja plicata for low-elevation swamps, and Chamaecyparis nootkatensis for higher elevation and northern swamps.
Vegetation Hierarchy
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
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 (= Rhododendron groenlandicum), Myrica gale, Trichophorum caespitosum, 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.
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.]

Related Type Name:

Short Citation:
  • Chappell 1999
  • Christy 2004
  • Faber-Langendoen et al. 2017a
  • Kunze 1994
  • MacKenzie and Moran 2004
States/Provinces:AK, BC, CA, OR, WA
Nations:CA, US
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.
US Forest Service Ecoregions
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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).
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, Chamaecyparis nootkatensis (= Callitropsis nootkatensis), Fraxinus latifolia, Picea sitchensis, Pinus contorta var. contorta, Thuja plicata, Tsuga heterophylla, and/or Tsuga mertensiana. Shrub species include Cornus sericea, Elliottia pyroliflorus, 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 Chamaecyparis 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.
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.
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.
D. Meidinger and G. Kittel      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. 2010-2017a. 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.

USNVC Credits: Detailed Description of the National Vegetation Classification Types

Date Accessed:

To cite a description:
Author(s). publicationYear. Description Title [last revised revisionDate]. United States National Vegetation Classification. Federal Geographic Data Committee, Washington, D.C.

About spatial standards:
The United States Federal Geographic Data Committee (hereafter called the FGDC) is tasked to develop geospatial data standards that will enable sharing of spatial data among producers and users and support the growing National Spatial Data Infrastructure (NSDI), acting under the Office of Management Budget (OMB) Circular A-16 (OMB 1990, 2000) and Executive Order #12906 (Clinton 1994) as amended by Executive Order #13286 (Bush 2003). FGDC subcommittees and working groups, in consultation and cooperation with state, local, tribal, private, academic, and international communities, develop standards for the content, quality, and transferability of geospatial data. FGDC standards are developed through a structured process, integrated with one another to the extent possible, supportable by the current vendor community (but are independent of specific technologies), and publicly available.

About this document
This document contains type descriptions at the Division level of the U.S. National Vegetation Classification. These descriptions were primarily written by NatureServe ecologists in collaboration with Federal Geographic Data Committee Vegetation Subcommittee and a wide variety of state, federal and private partners as a part of the implementation of the National Vegetation Classification. Formation descriptions were written by the Hierarchy Revisions Working Group. The descriptions are based on consultation with natural resource professionals, published literature, and other vegetation classification systems. The Ecological Society of America's Panel on Vegetation Classification is responsible for managing the review and formal adoption of these types into the National Vegetation Classification. Partners involved in the implementation of the USNVC include:

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  • Department of Defense (DOD)
  • Department of the Interior (USDI)
  • Forest Service (FS) - Chair
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Non U.S. Government
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Given the dynamic nature of the standard, it is possible a type description is incomplete or in revision at the time of download; therefore, users of the data should track the date of access and read the revisions section of the website to understand the current status of the classification. While USNVC data have undergone substantial review prior to posting, it is possible that some errors or inaccuracies have remained undetected.

For information on the process used to develop these descriptions see:

Faber-Langendoen, D., T. Keeler-Wolf, D. Meidinger, D. Tart, B. Hoagland, C. Josse, G. Navarro, S. Ponomarenko, J.-P. Saucier, A. Weakley, P. Comer. 2014. EcoVeg: A new approach to vegetation description and classification. Ecological Monographs 84:533-561 (erratum 85:473).

Franklin, S., D. Faber-Langendoen, M. Jennings, T. Keeler-Wolf, O. Loucks, A. McKerrow, R.K. Peet, and D. Roberts. 2012. Building the United States National Vegetation Classification. Annali di Botanica 2: 1-9.

Jennings, M. D., D. Faber-Langendoen, O. L. Louckes, R. K. Peet, and D. Roberts. 2009. Standards for associations and alliances of the U.S. National Vegetation Classification. Ecological Monographs 79(2):173-199.

FGDC [Federal Geographic Data Committee]. 2008. Vegetation Classification Standard, FGDC-STD-005, Version 2. Washington, DC., USA. []

For additional information contact:

  • Implementation of the U.S. National Vegetation Classification Standard - Alexa McKerrow (
  • NatureServe's Development of NVC Type Descriptions - Don Faber-Langendoen (don_faber-
  • Ecological Society of America's Review of the Type Descriptions
  • Federal Geographic Data Committee - Vegetation Subcommittee's Activities - Marianne Burke (
T. Boucher, C. Chappell, M.S. Reid, and D. Faber-Langendoen