Invalid Unit Specified
Macrogroup Detail Report: M028
Populus deltoides - Fraxinus pennsylvanica / Salix spp. Flooded & Swamp Forest Macrogroup

The U.S. National
Vegetation Classification
These deciduous forests and woodlands, dominated by Populus deltoides, Fraxinus pennsylvanica, and other hardwoods, are found along floodplains of permanent rivers in the prairie-dominated landscapes of the western and central Great Plains from southern Canada to northern Texas.
Collapse All::Expand All
Translated Name:Eastern Cottonwood - Green Ash / Willow species Flooded & Swamp Forest
Colloquial Name:Great Plains Flooded & Swamp Forest
This macrogroup is composed of woodlands and forests found along large to small rivers in the western and central Great Plains from southern Canada to the Texas panhandle. Populus deltoides is the most common tree and may be nearly the only species in the overstory in some stands. Other common trees are Acer negundo, Fraxinus pennsylvanica, Salix nigra, Salix amygdaloides, and, in the southeastern portion of this macrogroup's range, Celtis laevigata and Platanus occidentalis. The shrub and herbaceous layers are much more diverse than the canopy across the range of this macrogroup with no single species common throughout. Typical shrubs include Artemisia cana ssp. cana, Cornus spp., Salix spp., and Symphoricarpos occidentalis. The herbaceous stratum is strongly influenced by surrounding upland Great Plains grasslands and often contains mid- and tallgrass species.
This macrogroup is dominated by trees and is found along large to small rivers in the Great Plains. Its range in the drier central and western Great Plains and the presence of more Great Plains flora in the understory help to distinguish it from floodplain macrogroups farther east.
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.Na Eastern North American-Great Plains Flooded & Swamp Forest D011 1.B.3.Na
Macrogroup M028 Great Plains Flooded & Swamp Forest M028 1.B.3.Na.4
Group G147 Great Plains Cottonwood - Green Ash Floodplain Forest G147 1.B.3.Na.4.a
This macrogroup is often quite distinct from surrounding upland grassland or shrubland vegetation. Where small tributaries or draws join with medium or small rivers, this macrogroup could be adjacent to Great Plains Forest & Woodland Macrogroup (M151). This macrogroup (M028) is distinguished by being in floodplains where regular flooding occurs and often has Populus deltoides and/or Salix spp. as a dominant or significant component of the overstory and Salix spp. in the shrub layers.
Synonomy: < Cottonwood - Willow: 235 (Eyre 1980)
> Cottonwood: 63 (Eyre 1980)
> Sugarberry - American Elm - Green Ash: 93 (Eyre 1980)

Related Type Name:

Short Citation:
  • Brown and Matthews 1995
  • Eyre 1980
  • Faber-Langendoen et al. 2017a
  • Weaver 1960
States/Provinces:AB, CO, KS, MB, MT, ND, NE, NM, OK, SD, SK, TX, WY
Nations:CA, US
Range:This macrogroup is found along permanent rivers throughout the western and central Great Plains from the southern Prairie Provinces of Canada to the panhandle of Texas and from the Rocky Mountains east to the eastern Dakotas, Nebraska and Kansas.
US Forest Service Ecoregions
Domain Name:
Division Name:
Province Name:
Province Code:   Occurrence Status:
Section Name:
Section Code:     Occurrence Status:
Stands in this dynamic macrogroup can have a wide variety of physiognomies. The tree canopy, with trees >5 m, can be open to partly closed (10-60%) and the shrub and herbaceous strata can range from nearly absent to closed (<60%).
Populus deltoides is the most common tree across the range of this macrogroup, and some stands may contain little else in the canopy. Several other tree species can be present to even dominant in some stands. These include Acer negundo, Fraxinus pennsylvanica, Salix nigra, Salix amygdaloides, and, in the southeastern portion of this macrogroup's range, Celtis laevigata and Platanus occidentalis. The shrub and herbaceous layers are much more diverse than the canopy across the range of this macrogroup. Typical shrubs include Artemisia cana ssp. cana, Cornus drummondii, Cornus sericea, Salix interior, Salix exigua, and Symphoricarpos occidentalis. Prunus spp. can occur, especially along drier edges of these floodplains. The herbaceous stratum is strongly influenced by surrounding upland Great Plains grasslands and often contains mid- and tallgrass species such as Andropogon gerardii, Carex pellita, Pascopyrum smithii, Panicum virgatum, Schizachyrium scoparium, Spartina pectinata, and Sporobolus cryptandrus. Portions of floodplains that retain water longer, typically in or adjacent to larger prairie rivers, can have pockets of marsh vegetation such as Typha spp., Schoenoplectus fluviatilis (= Scirpus fluviatilis), and Schoenoplectus tabernaemontani (= Scirpus validus) in moderate to deep water and Alisma spp., Phalaris arundinacea, Sagittaria latifolia, and Sparganium eurycarpum in the shallowest areas (Weaver 1960). Where these pockets are large, they fall into a different macrogroup.
This macrogroup is found in floodplains and riparian settings along large to small rivers. Soils are primarily alluvial and range from sandy to clay. This macrogroup can occur in deep or shallow river valleys but slopes within stands are typically gentle or nonexistent.

Larger and broader river valleys may have a natural levee near the main channel, behind which a poorly drained backswamp can form. These riparian swamps do not flood as often and retain water from upland drainage, as well as from larger floods, so the hydrology is somewhat different than that on the levee or in floodplains with no levees. Backswamps in this macrogroup are not as wet as those associated with larger rivers to the east but larger and wetter occurrences can grade into ~Great Plains Marsh, Wet Meadow, Shrubland & Playa Macrogroup (M071)$$ where the tree canopy is sparse or absent or into ~Central Hardwood Floodplain Forest Macrogroup (M029)$$ where the swamps become more permanently wet.

Currently, many stands persist on rivers that have been dammed and where flooding is now largely absent.
Periodic flooding is important in establishing and maintaining stands of this macrogroup. Flooding regime (frequency, severity, duration) is also important in shaping the understory composition and structure. Flooding regime is highly variable across the region and from year-to-year. In general, floods are most likely from late-fall to late-spring across the region. Streams in the north and west of the range of this macrogroup are more influenced by snowmelt and have more predictability of flow with spring maximum flow rates (Brown and Matthews 1995). Fire may spread from surrounding uplands, particularly where the understory has a significant herbaceous component.
J. Drake      Version Date: 15Oct2014

  • Brown, A. V., and W. J. Matthews. 1995. Stream ecosystems of the central United States. Pages 89-116 in: C. E. Cushing, K. W. Cummins, and G. W. Minnshall, editors. Ecosystems of the Worlds. Volume 22: River and Stream Ecosystems. Elsevier Science, Amsterdam.
  • Eyre, F. H., editor. 1980. Forest cover types of the United States and Canada. Society of American Foresters, Washington, DC. 148 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. 2010-2017a. Divisions, Macrogroups and Groups for the Revised U.S. National Vegetation Classification. NatureServe, Arlington, VA. plus appendices. [in preparation]
  • Weaver, J. E. 1960. Flood plain vegetation of the central Missouri Valley and contacts of woodland with prairie. Ecological Monographs 30:37-64.

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 Macrogroup 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:

U.S. Government
  • Department of Agriculture (USDA)
  • Department of Commerce (DOC)
  • Department of Defense (DOD)
  • Department of the Interior (USDI)
  • Forest Service (FS) - Chair
  • National Agriculture Statistical Service (NASS)
  • Natural Resources Conservation Service (NRCS)
  • National Oceanic and Atmospheric Administration (NOAA)
  • National Marine Fisheries Service (NMFS)
  • U.S. Army Corps of Engineers (USACE)
  • U.S. Navy (NAVY)
  • Bureau of Land Management (BLM)
  • Fish and Wildlife Service (FWS)
  • National Park Service (NPS)
  • U.S. Geological Survey (USGS)
  • Environmental Protection Agency (EPA)
  • National Aeronautics and Space Administration (NASA)
Non U.S. Government
  • NatureServe (NS)
  • Ecological Society of America (ESA)

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 (