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

CHAPTER 2, COMMUNITY COMPONENTS: PLANTS2.1 I NTRODUCT I ONThe physical characteristics whichdistinguish tidal freshwater wetlands (seeSection 1.1) exert considerable influenceon plant communi ty development. Nearlyall of these wetlands are riverine. Thelack of stressful sal ini ty levels facil i-tates util ization of this habitat by manymore plant species than are found incoastal or inland brackish marshes. Suchhigh diversity produces a co~nplex andseasonally variable mixture of 1 ife forms.Unl ike nontidal riparian wet1 ands wheremarsh vegetation is confined to a narrowband para1 lel i ny channel s, regular inundationin tidal freshwater regions serves tolaterally extend habitat boundaries.Plant communities visibly stratify acrossthis broadened niche space, a1 though distinctzonation is not readily apparent.No known plant species appears exclusivelyin the tidal freshwater habitat.Most marshes are dominated by a combinationof annuals and perennial s, the majority of which are common to freshwater wetlandsover nuch of North America (Fassett1957, Cowardin et al. 1979; Silberhorn1982). Latitudinal differences in cl imateas well as local variation in physiographyand geology produce distinct heterogeneitywithin tidal freshwater marshes. Marshesin respective regions of the At1 anticcoast differ markedly in plant speciesconposi tion, re1 ative diversity, and community structure as a result of this variation.A1 though tidal freshwater marshesshare much in common with other wetlandsas a whole, only a limited amount ofavail able information pertains specificallyto the flora and ecology of thishabitat.The discussion which follows willfocus upon those plant species which mostcommonly occur in tidal freshwater marshes.Emphasis will be placed on descriptionsof community structure and thosephysical and ecological processes influencingplant demography and succession.Habitat vari abil i ty on a regional basiswill be discussed, a1 though in most instancesthe tidal marshes of the mid-Atlantic States will serve as a generalmodel. Plant species are addressed bycommon names in the text; scientific namesare listed in Appendix A.2.2 GENERAL SPECIESIHABITAT DESCRIPTIOI\ISThe bulk of tidal freshwater marshf1 ora consists of (1) broad-1 eaved emergentperennial macrophytes (spatterdock,arrow-arum, pickerelweed, arrowheads), (2)herbaceous annuals (smartweeds, tearthumbs,burmari go1 ds, jewelweed, giantragweed, water-henp, water-dock) , (3) annualand perennial sedges, rushes andgrasses (bulrushes, spi ke-rushes, umbrella-sedges,rice cutgrass, wild rice, giantcutgrass), (4) grass1 i ke plants or shrubformherbs (sweetflag, cattail ,. rosenallow,water parsnip), and (5) a handfulof hydrophytic shrubs (button bush, waxmyrtle,swamp rose) (Whigham et al. 1976;Tiner 1977; McCormick and Sornes 1982;Metzler and Rosza 1982; Sil berhorn 19821.Regional variations in species compositionand diversity persist, but havenever been described comparatively.Marshes of the %id-Atlantic and GeorgiaBight regions can contain as many as 50 to60 species at a single location, and arecomprised of a number of codominant taxa(Odum 1978; Sandifer et al. 1980). Amongthe more conspicuous species occurring inboth regions are arrow-arum, pickerelweed,wild rice, and cattails. However, thereare notable differences between the tidal