Physiognomy and Structure: No Data Available

Floristics: Overstory composition is somewhat limited, with Fraxinus pennsylvanica usually codominant with Acer rubrum, Acer saccharinum, or both. Occasional stands vary toward near-monospecific dominance by one of these three species. In Virginia and Maryland, Acer saccharinum is most characteristic of large-river (e.g., the James and Potomac) floodplains, where Acer rubrum is nearly absent. On the smaller order streams that support this type, Acer saccharinum is usually absent. Ulmus americana is a constant minor overstory associate and usually dominates the subcanopy layers when these are developed. Occasional overstory and understory associates include Acer negundo, Betula nigra, Platanus occidentalis, Quercus bicolor, and Quercus palustris. The shrub layer is typically very sparse or absent but may include tree saplings of Carpinus caroliniana as well as Cephalanthus occidentalis, Cornus amomum, and Lindera benzoin. Vines, especially Toxicodendron radicans, Parthenocissus quinquefolia, and Vitis spp., are common. The herb layer is usually moderately dense or dense except in deeper hollows. Boehmeria cylindrica is the most constant herb in 11 Maryland and Virginia plots, averaging 5 to 10% cover. Saururus cernuus and Impatiens capensis are less constant (55% of plots) but may be high-cover patch-dominants where they occur. Other characteristic and occasionally abundant herbs include Cinna arundinacea, Geum canadense, Glyceria striata, Leersia virginica, Polygonum arifolium, Polygonum punctatum, Pilea pumila, Lobelia cardinalis, Ludwigia palustris, Commelina virginica, Carex stipata, Carex grayi, Carex tribuloides, Carex crinita, and Carex lupulina. In the northern part of the range, examples may contain patches of Symplocarpus foetidus. The invasive exotic Lysimachia nummularia is problematic in many stands. At Mammoth Cave National Park (Kentucky), the canopy is dominated by Fraxinus pennsylvanica, with Acer rubrum and Platanus occidentalis also common. The shrub zone is sparse with Cephalanthus occidentalis dominant; the understory is mostly open. The herb layer is dominated by Saururus cernuus. Other common herbs include Carex grayi, Chasmanthium latifolium, Leersia virginica, Ludwigia palustris, and Sagittaria latifolia.

Dynamics:  The habitat occupied by this association limits floristic composition to species with high tolerances for relatively deep and prolonged inundation. The relationship between this type and similar types dominated by oaks (e.g., ~Quercus palustris - Quercus bicolor / Carex tribuloides - Carex radiata - (Carex squarrosa) Wet Forest (CEGL006497)$$) is complex and not fully understood. Field observations (VDNH unpubl. data) of mean flooding depths in various communities suggest that some stands of this type occupy habitats that are too deeply flooded to support hydrophytic oaks. The clearest support for this hypothesis is found in large floodplains that support both types of swamp along an apparent hydrologic gradient. At other sites, especially on smaller streams, it appears that these communities may have a successional relationship in which cut-over or formerly cleared stands of oak-dominated swamp forest have regenerated in stands dominated by Fraxinus pennsylvanica and Acer rubrum. Along the Potomac in the Chesapeake and Ohio National Historical Park, there are examples with even dominance of Quercus palustris and Acer saccharinum classified as Acer (rubrum, saccharinum) - Fraxinus pennsylvanica - Ulmus americana / Boehmeria cylindrica Forest (CEGL006548).