Physiognomy and Structure: No Data Available

Floristics: These are open forests to woodlands with the tree canopy dominated by Quercus rubra, Quercus shumardii, Fraxinus americana, and Carya cordiformis. Minor overstory associates include Quercus alba, Ulmus americana, Juglans nigra, Ulmus rubra, Quercus bicolor, and Celtis occidentalis. Quercus macrocarpa is a Maryland state-rare species that occurs in this type. The subcanopy layers are poorly developed. The shrub layer ranges from very open (on the Maryland side) to fairly dense (on the Virginia side); Cercis canadensis is a constant and characteristic shrub throughout, while Carpinus caroliniana, Asimina triloba, and Ptelea trifoliata are common in the Virginia stands. The herbaceous layer also varies dramatically on the two sides of the river. The Maryland stands are dominated by tall, weedy native species, primarily Ageratina altissima and Teucrium canadense, with Verbesina alternifolia and Symphyotrichum lateriflorum (= Aster lateriflorus) also common. These weedy herbs are much less abundant in the Virginia stands, which are dominated by graminoids, primarily Elymus hystrix var. hystrix, Elymus villosus, Elymus virginicus, Dichanthelium boscii, Festuca subverticillata, and Chasmanthium latifolium, which are entirely absent from the Maryland stands. Mesophytic forbs such as Amphicarpaea bracteata, Galium concinnum, and Packera aurea are also common in the Virginia stands, which have a notably higher mean species richness (n = 82 taxa per 400 m2) than their Maryland counterparts (n = 54 taxa per 400 m2). The invasive introduced grass Microstegium vimineum is rampantly abundant in parts of this association.

Dynamics:  The unusual combination of tall, disturbance-adapted herbs of low floodplains, upland herbs, and trees of higher floodplains and uplands is probably due to the combination of frequent flooding and seasonal dryness. This vegetation type is apparently somewhat spatially ephemeral in that it represents a transition from depositional processes to erosional processes and may "migrate" upstream with the Potomac River channel knickpoint at Great Falls. The type would be converted to a channel shelf (and eventually, a channel) type if attacked by erosion, or to a more xeric terrace type if it remained elevated on an interfluve between two deepening channels. Construction of the Washington Aqueduct diversion dam (weir) just above Great Falls may have stalled new formation of this type or converted existing examples of it (prior to 1857) by increasing the rate of deposition on surfaces that were once more conducive to formation of this type. Conn Island, which is located just above the dam, was evidently continuous with present-day Great Falls and Olmsted Island prior to this construction and may have supported this type. There is some evidence of this hypothesis in the frequency of Quercus rubra on the Conn Island floodplain.