Physiognomy and Structure: The tree layer is dominated by tall (20-35 m in height) single-stemmed deciduous species. The canopy is overlapping, generally forming 60-100% cover. The shrub layer is also dense with up to 60% cover, and often multi-tiered, with both tall and short shrubs. The herbaceous layer is dominated by forbs with up to 20% cover. In parts of this alliance''s range, graminoid cover is primarily from introduced grass species.

Floristics: Communities within this alliance are characterized as cold-deciduous, temporarily flooded forests. The tree and shrub layers are dominated by Populus deltoides ssp. wislizeni or Populus deltoides ssp. monilifera with cover varying from 15-85% cover. Older, more mature stands will be characterized by a few large (up to 1 m diameter at breast height) trees with less canopy cover but larger basal area. Other trees occasionally present include Populus angustifolia, Populus x acuminata, Salix amygdaloides, and Salix gooddingii. In Arizona, the canopy tree may be a hybrid with Populus fremontii x Populus deltoides ssp. wislizeni. In the New Mexico stands, the understory has a shrub layer of varying cover characterized by Baccharis salicifolia (= Baccharis glutinosa), Baccharis sarothroides, Fallugia paradoxa, Forestiera pubescens (= Forestiera neomexicana), Gutierrezia sarothrae, and Juniperus monosperma. Colorado stands include scattered Artemisia tridentata ssp. tridentata and Ericameria nauseosa. The liana Clematis ligusticifolia may be present in some stands. The herbaceous layer is generally sparse to moderate, and many stands have introduced grass species. Graminoids present in relatively undisturbed stands may include Distichlis spicata, Eleocharis palustris, Muhlenbergia asperifolia, and Muhlenbergia emersleyi. Forb cover is sparse except in disturbed sites, where aggressive exotic species such as Acroptilon repens or Lepidium latifolium may dominate the herbaceous stratum.

Dynamics:  Cottonwood forests grow within an alluvial environment that is continually changing due to the ebb and flow of the river. Riparian vegetation is tolerant of, and indeed reliant on, flooding disturbance. Cottonwood communities are early-, mid- or late-seral, depending on the age class of the trees and the associated species of the stand. Mature cottonwood stands do not regenerate in place, but regenerate by germinating in different locations up or downstream. Over time, a healthy riparian area supports many stages of cottonwood communities. The process of cottonwood regeneration is well-documented. Periodic flooding events can leave sandbars of bare, mineral substrate. Cottonwood seedlings germinate and become established on newly-deposited, moist sandbars. In the absence of large floods in subsequent years, seedlings begin to trap sediment. In time, the sediment accumulates and the sandbar rises. The young forest community is then above the annual flood zone of the river channel. In this newly elevated position, with an absence of excessive browsing, fire, or agricultural conversion, this cottonwood community can grow into a mature riparian forest. At the same time, the river channel continually erodes streambanks and creates fresh, new surfaces for cottonwood establishment. This results in a dynamic patchwork of different age classes, plant associations and habitats. As cottonwoods mature, other tree species may become established. If the land surface is subject to reworking by the river, the successional processes will start over with erosion and subsequent flooding deposition. If the land surface is not subject to alluvial processes, for example on a high terrace, the cottonwoods will be replaced by upland shrub or tree species from adjacent areas.