The Ecology of Tidal Freshwater Marshes of the - USGS National ...

able physiognonies in this species mightbe considered analogous to the heightforins of smooth cordgrass whi ch del ineatezones in salt narshes.Where zonation, as an organizationalexpression of species distributions, actuallyexists in the tidal freshwater marshhabitat, it is probably controlled by acombination of physical variables and eco-1ogi cal processes. Prel irninary evidencesugyests that there may be a certain degreeof consistency in the zonation foundin tidal freshwater oarshes. However, theextent of this patterning with respect tovarious community types, as we1 1 as itsregularity frorn location to location, isunknown.species within a general structural frameworkfor tidal freshwater wetlands. As afirst approximation to community structurewithin this habitat, most of the comnon1.yoccurring vegetation fa1 1 s into one of thefol lowing categories: (1) submerged orfloating-leaved plants, ( ) emergentplants with basal leaves and/or leaflessstems, (3) emergent or damp soil herbswith stems bearing alternate or opposite1 eaves ,. (4) grass1 ike or rush1 i ke ol ants,and (5) broad-1 eaved shrubs and trees(Magee 1381). By recognizing the aporoximatemodal distributions of common plantspecies or communi ty-type indicatorspecies within these structural subgroups,a typical marsh profile can be visual izedand described.The Marsh ProfileThe marsh profile de~icted in Fiqure13 is most characteristic of mid-AtlanticExcept for the most obvious community tidal marshes. Seds of submerqed, rootedtypes, it is difficult to place a given aquatic plants (see Section 2.6) make upBALD CYPRESS - BLACK GUMWAX-MYRTLEWILD RICEGlA NT CUTGRASS4 CATTAILSEDGES - RUSHESBIG CORDGRASSIIIIIROSE-MALLOWJEWELWEED3 BURMA RlGOL DTEARTHUMBSMARTWEED1ARROW-ARUMPICKERELWEEDI IIIIII I I I IHIGH MARSHWOODED SWAMP1FORESTED UPLANDFigure 13.Characteristic profile of mid-At1 antic tidal freshwater marsh.25