Invalid Unit Specified
CEGL000939 Populus deltoides (ssp. wislizeni, ssp. monilifera) / Distichlis spicata Riparian Woodland

The U.S. National
Vegetation Classification
Type Concept Sentence:
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Common (Translated Scientific) Name: (Rio Grande Cottonwood, Plains Cottonwood) / Saltgrass Riparian Woodland
Colloquial Name: Cottonwood / Saltgrass Riparian Woodland
Hierarchy Level: Association
Type Concept: This riparian woodland association is described from major river systems of eastern Colorado, primarily the South Platte and Arkansas rivers and their major tributaries in the plains. It also occurs in the floodplains of the Yampa and Green rivers in northwestern Colorado. Stands may also occur in western Nebraska, New Mexico, eastern Wyoming and northeastern Utah. Sites are floodplains of major streams and rivers at elevations ranging from 1000 to 1700 m (3280-5600 feet). The floodplains of these rivers are typically wide and flat with a variety of depositional features present. Stands occur on higher terraces away from the active floodplain, where the soil surface is drier, but trees are able to tap the deeper water table. Flooding is infrequent on these terraces. Soils are well-drained, alkaline, poorly developed and typically derived from alluvium, eolian deposits and shale. A relatively open canopy of the broad-leaved deciduous tree Populus deltoides characterizes these woodlands, with cover varying from roughly 20% to over 70%. Other deciduous trees are occasionally present, including the natives Salix amygdaloides and Acer negundo, and several introduced species such as Fraxinus pennsylvanica, Tamarix spp., Ulmus spp., and Elaeagnus angustifolia. The shrub layer is poorly developed or entirely absent. Shrubs, when present, include Ribes aureum, Rosa woodsii, Salix exigua, Symphoricarpos orbiculatus, Toxicodendron radicans, and introduced Tamarix spp. The sparse to dense herbaceous layer is dominated by the perennial grass Distichlis spicata (6-70% cover). Herbaceous cover varies with tree canopy closure in that the more open woodlands have denser graminoid cover. Sporobolus cryptandrus, Elymus canadensis, and Pascopyrum smithii are other common perennial grasses. Many other graminoid and forb species may be common, including several introduced species, especially in disturbed stands.
Diagnostic Characteristics: No Data Available
Rationale for Nominal Species or Physiognomic Features:
Classification Comments: No Data Available
Similar NVC Types:
Populus deltoides (ssp. wislizeni, ssp. monilifera) / Pascopyrum smithii Riparian Woodland, note:
Populus deltoides / Muhlenbergia asperifolia Flooded Forest, note:
Populus deltoides (ssp. wislizeni, ssp. monilifera) / Sporobolus airoides Flooded Woodland, note:
Physiognomy and Structure: No Data Available
Floristics: This association is characterized by a relatively open canopy of the broad-leaved deciduous tree Populus deltoides ssp. monilifera in the Great Plains and the eastern third of New Mexico; Populus deltoides ssp. wislizeni occurs in western Colorado and New Mexico. Canopy cover varies from roughly 20% to more than 70%. In most stands the trees are large and uniformly sized, but density varies from 45 to 115 trees per hectare. Young Populus deltoides are absent from the community. Other deciduous trees are occasionally present, including the natives Salix amygdaloides and Acer negundo, and introduced species such as Fraxinus pennsylvanica, Tamarix spp., Ulmus americana, and Elaeagnus angustifolia. The shrub layer is poorly developed or absent, but broad-leaved deciduous shrubs occasionally occur. Species can include Ericameria nauseosa, Ribes aureum, Rosa woodsii, Rhus trilobata, Salix exigua, Symphoricarpos orbiculatus, and Toxicodendron radicans. The herbaceous layer is dominated by the perennial grass Distichlis spicata, with highly variable cover (from 6% to over 70%). This variation is apparently related to the degree of tree canopy closure in that more open stands of Populus have denser graminoid cover in the understory. Sporobolus cryptandrus, Elymus canadensis, and Pascopyrum smithii (= Agropyron smithii) are other common perennial grasses but with less cover. The remainder of the herbaceous layer typically is a mix of graminoid, horsetail and forb species, and in most stands includes many introduced species, both annual and perennial. Total herbaceous cover is highly variable. Cryptograms are very uncommon. The highly invasive species Elymus repens may replace Distichlis spicata in some stands. Most of the stands along the Arkansas River have a dense layer of the introduced forb Bassia scoparia (= Kochia scoparia). Additionally, Tamarix chinensis (introduced) is highly invasive and has come to dominate many cottonwood stands along the Arkansas. This exotic species is actually impeding establishment of Populus seedlings on freshly deposited sandbars. The highly invasive species Tamarix ramosissima has come to dominate many cottonwood stands along the Arkansas and Yampa rivers.
Dynamics: This is a transitional association as it occurs on floodplain terraces that flood only rarely and are somewhat to very isolated from the water table. Under these circumstances, Populus deltoides will not regenerate but will gradually give way to upland species such as Rhus trilobata, Ericameria nauseosa, and Artemisia tridentata ssp. tridentata. Distichlis spicata dominates the understory primarily because of alkaline soil conditions, but drainage may also be poor because of lack of slope and/or subsurface clay lenses impeding infiltration.

This association may be more abundant today than in presettlement times. Before the large rivers of Colorado were hydrologically modified, frequent spring flood scouring and severe summer droughts discouraged the growth of trees within the active floodplain. Dams and diversions have eliminated both flooding and drying of the system, as well as causing rivers to adhere to a single channel, which has allowed seedlings of both Populus deltoides and Tamarix spp. to survive to maturity.
Environmental Description: This type occurs on floodplains of major streams and rivers within the western portion of the Great Plains, as well as on the floodplains of larger streams of the Colorado Plateau. The climate is semi-arid and continental. Annual precipitation can fluctuate widely, varying from less than 25.4 cm (10 inches) to over 40.6 cm (16 inches), which falls mostly as summer rains in the Great Plains and is more evenly distributed throughout the year in the Colorado Plateau. Winters are short, with extreme variations in temperatures. Summers are long and hot.

Geologically, the region is underlain by sedimentary rock, which in some areas approaches the surface. Overlying layers, both on the uplands and within the river valleys, are primarily unconsolidated sediments. Deposits on the Great Plains are primarily Pleistocene glacial outwash, with some areas of eolian deposits (loess and sandhills). On the Colorado Plateau, rivers flow alternately through narrow canyons of sandstone and other resistant rocks and broad valleys formed in softer shales, where alluvium deposited over millennia forms broad floodplains. Elevations range from about 1070 to 1525 m (3500-5000 feet) on the Great Plains and are generally below 1710 m (5600 feet) on the Plateau River valleys. Both regions have gentle slopes, falling an average of 2-3 m (7-9 feet) per mile.

The floodplains of these rivers are typically wide and flat. A variety of depositional and erosional features are present within the floodplain, such as active channels, overflow channels, terraces and alluvial fans. This association occurs on higher terraces away from the active floodplain, where the soil surface is drier, but trees are able to tap the deeper water table. Flooding is infrequent on these terraces. Soils are derived from alluvium, eolian deposits and sometimes shales. They are not well-developed and have a typical structure of bands or lenses of sand, clay, silt and gravel. They are low in organic matter and often are alkaline.
Geographic Range: This association occurs on the high plains east of the Rocky Mountain front in Colorado, as well as on the Colorado Plateau. Similar associations have been reported for eastern Wyoming and western Nebraska (Jones and Walford 1995, G. Steinauer pers. comm. 1997). This association is likely also to occur in New Mexico and northeastern Utah.
Nations: US
States/Provinces: CO, NE?, NM?, UT, WY?
US Forest Service Ecoregions (1994/1995)
Domain Name:
Division Name:
Province Name: Southern Rocky Mountain Steppe - Open Woodland - Coniferous Forest - Alpine Meadow Province
Province Code: M331    Occurrence Status: Confident or certain
Section Name: Uinta Mountains Section
Section Code: M331E     Occurrence Status: Confident or certain
US Forest Service Ecoregions (2007)
Domain Name:
Division Name:
Province Name: Southern Rocky Mountain Steppe - Open Woodland - Coniferous Forest - Alpine Meadow Province
Province Code: M331    Occurrence Status: Confident or certain
Section Name: Uinta Mountains Section
Section Code: M331E     Occurrence Status: Confident or certain
Omernik Ecoregions:
Confidence Level: Low
Confidence Level Comments:
Grank: G2
Greasons: This association occurs along low-elevation rivers in a semi-arid region where agricultural activities and hydrologic modifications have had great impacts. Existing occurrences are found on the high plains east of the Rocky Mountain front in north-central and northeastern Colorado and along the Yampa River in northwestern Colorado. Similar associations have been reported for eastern Wyoming and western Nebraska (Jones and Walford 1995, G. Steinauer pers. comm. 1997). The Populus deltoides ssp. wislizeni form of this association is likely to occur also in western New Mexico and northeastern Utah. Water impoundments have altered the natural flood regimes; floodplains are used for pastures, hay fields and livestock grazing. Introduced species have invaded and, in the case of Tamarix, have increased soluble salts in the soils. The area of ~Populus deltoides (ssp. wislizeni, ssp. monilifera) / Distichlis spicata Riparian Woodland (CEGL000939)$$ on the Arkansas River is small and apparently is decreasing due to the above reasons. The acreages of this association along the Arkansas and South Platte rivers are 2761 and 17,166 acres, respectively (1970 data). Stands along the Yampa River in and near Dinosaur National Monument total less than 10 acres. Most stands on the South Platte are composed of older trees.
Concept Lineage:
Predecessors:
Obsolete Names:
Obsolete Parents:
Synonomy: = Populus deltoides / Distichlis spicata Woodland (Faber-Langendoen 2001)
= Populus deltoides / Distichlis spicata Woodland (Carsey et al. 2003a)
Concept Author(s): M.S. Reid
Author of Description: M.S. Reid and J. Coles
Acknowledgements:
Version Date: 07Sep2005
References:
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