Common (Translated Scientific) Name: Eastern Cottonwood - Green Ash / Willow species Flooded & Swamp Forest
Colloquial Name: Great Plains Flooded & Swamp Forest
Hierarchy Level: Macrogroup
Type Concept: 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.
Diagnostic Characteristics: 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.
Rationale for Nominal Species or Physiognomic Features:
Classification Comments: 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.
Similar NVC Types:
M029 Central Hardwood Floodplain Forest, note: "has more frequent and longer duration flooding, and few mixed grass or tallgrass prairie species in the understory; Acer saccharinum, Celtis laevigata, and Platanus occidentalis can be abundant."
M154 Southern Great Plains Floodplain Forest & Woodland, note:
M151 Great Plains Forest & Woodland, note:
Physiognomy and Structure: 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%).
Floristics: 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., Bolboschoenus 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.
Dynamics: 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.
Environmental Description: 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.
Geographic 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.
Nations: CA, US
States/Provinces: AB, CO, KS, MB, MT, ND, NE, NM, OK, SD, SK, TX, WY
|US Forest Service Ecoregions (2007)|
Southwest Plateau and Plains Dry Steppe and Shrub Province
Confident or certain
Western Great Plains Section
Confident or certain
Confidence Level: Moderate
Confidence Level Comments:
Populus deltoides - Fraxinus pennsylvanica / Salix spp. Flooded Forest Macrogroup
Great Plains Floodplain Forest
Synonomy: < Cottonwood - Willow: 235 (Eyre 1980)
> Cottonwood: 63 (Eyre 1980)
> Sugarberry - American Elm - Green Ash: 93 (Eyre 1980)
Concept Author(s): S. Menard, K. Kindscher, P. Comer, G. Kittel, in Faber-Langendoen et al. (2014)
Author of Description: 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. 2010-2019a. 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.