Physiognomy and Structure: No Data Available

Floristics: This community is a riparian forest with an open to closed canopy dominated by deciduous trees. Girard et al. (1989) sampled two stands in southwestern North Dakota that had an average of 293 trees/ha. Hansen et al. (1984) sampled four stands that had an average basal area of 41 m2/ha and 427 trees/ha. They found that the average cover by strata was shrubs 76.8%, graminoids 64.2%, and forbs 43.5%. Populus deltoides and Fraxinus pennsylvanica are the most abundant mature trees. Acer negundo, Salix amygdaloides, and Juniperus scopulorum may also be present in the tree layer. This community is seral, and in younger stands Populus deltoides is the dominant, but as stands age Fraxinus pennsylvanica becomes more prominent until the stand becomes a different community. The closed canopy leads to poor reproduction by Populus deltoides in stands of all ages. The shrub layer is often vigorous. Species such as Rosa woodsii, Symphoricarpos occidentalis, Juniperus scopulorum, Juniperus communis, and Cornus sericea ssp. sericea can be abundant. The composition of the herbaceous layer is variable. Along the Missouri River, Keammerer (1972) found Poa pratensis to be the most prevalent species, with Amphicarpaea bracteata, Bromus inermis, and Elymus virginicus common. Carex spp., Juncus spp., Leymus cinereus, Lysimachia ciliata, Thalictrum venulosum, and Elymus canadensis are common. Weedy species are almost ubiquitous, among them are Poa spp., Bromus inermis, Melilotus officinalis, Ambrosia spp., and Urtica spp. Further comparisons are needed between stands in Nebraska, which may contain a different set of species, from those further north. See Steinauer and Rolfsmeier (2003) for a description of the Nebraska stands.

Dynamics:  The species dominating this community are pioneers of bare soil. The community is sometimes considered a "postclimax" type that exists in otherwise arid areas because of groundwater along streams and rivers. It is often subject to flooding, deterioration during periodic droughts, and destruction by herbicides, after which it reappears following natural seeding. In the southern portion of its range, cottonwood-willow forests on river bottomlands often contain an understory of Juniperus virginiana that has developed as a result of seed dissemination by birds from individuals in windbreak plantings on adjacent uplands. This conifer component may be gradually altering the type.

Girard (1985) stated that the condition of these woodland communities appears to be declining and suggests that improper or overgrazing by livestock is a significant factor. Flooding is necessary to reproduce the conditions on which this community can establish. Without periodic floods to create bare alluvium, this community cannot become established in new areas to take the place of those that are succeeding to later seral stages.