Tidal Wetlands Primer: An Introduction to Their Ecology, Natural History, Status, and Conservation

5. Tidal Wetland Types and their Vegetation

123 Many types of tidal wetlands occur across North America from the edge of the ocean to a point where tidal action ceases in coastal rivers (Figure 5.1). Tidal wetlands include both vegetated and nonvegetated types. The latter occur either at lower elevations in the intertidal zone or above mean high tide in regions where salts accumulate and raise soil salinities well above sea strength to levels that prevent colonization by macrophytic plants. Tidal wetlands can be classified in numerous ways based on a wide range of properties (see Chapter 1). For this chapter, I have divided them into types based on differences in the presence or absence of vascular plants, the nature of the substrate, the life form of the dominant vegetation, and the salinity of their associated tidal waters. Ten general types are described: beaches, tidal flats, rocky shores, salt marshes, estuarine shrub swamps, estuarine forests (including mangrove swamps), brackish marshes, tidal fresh marshes, tidal freshwater swamps, and coastal aquatic beds. While the descriptions emphasize tidal wetlands in the northeastern United States and eastern Canada, similar types elsewhere in the United States are addressed under the subheading Regional Differences and through the use of tables. Macroalgae are referenced where they dominate the habitat (e.g., rocky shores). Animals frequenting tidal wetlands are covered in Chapter 6. When reading the descriptions of coastal wetland types, readers must keep in mind the range limits of plant species, as some will not occur in certain estuaries of the northeastern United States or eastern­Canada. (Note: Two companion books— Field Guide to Tidal Wetland Plants of the Northeastern United States and Neighboring Canada [Tiner 2009] and Field Guide to Coastal Wetland Plants of the Southeastern United States [Tiner 1993a]—provide illustrations and descriptions including geographic ranges for most of the plants mentioned in this chapter.) Beaches In general, beaches are gently sloping sandy to cobbly shorelines found along the ocean and in coastal embayments (Figure 5.2). They may be miles long or restricted to narrow fringes along rocky headlands. The most familiar beaches are the sandy beaches of spits and barrier islands, but beaches may also be composed of cobble or gravel. These latter types are typical of rocky coastlines. Some cobble beaches have been called “musical beaches” for the sound made when the surf strikes the cobbles or when the swash recedes and the cobble stones strike one another, producing a rattling sound. Sandy beaches are most common south of Portland, Maine, and form a nearly continuous band along the Atlantic shoreline from Cape Cod south. From Long Island south, they occupy the oceanfront intertidal zone of a series of barrier islands. In northern 5 Tidal Wetland Types and Their Vegetation 124  Chapter 5 New England and eastern Canada, many beaches are cobble-gravel shorelines typified by rather large rounded cobbles. Sandy beaches, however, comprise much of the southern shore of the Gulf of St. ­ Lawrence including Prince Edward Island, the­ Magdalen Islands, Miscou Island, and the­ Northumberland Strait as well as sections of the southern shore of the St. Lawrence River. Two zones are frequently described for beaches: 1) the foreshore (flooded frequently by the tides), and 2) the backshore (directly in front of the primary dunes and flooded by storm tides). Some beaches have only foreshore areas. The foreshore includes both sloping and nearly level landforms, while the backshore is more or less flat. The foreshore slope encompasses the swash zone where waves wash up and down the shore. A terrace or berm forms above this zone where sediments build up. Some beaches lack the berm, while in others the shape and number of berms may change from summer to winter due to seasonal beach erosion and accretion patterns (Leatherman 1979). In the Northeast, winter beaches tend to be narrower and steeper than summer beaches because winter storms generate higher tides, causing more erosion. Summer wave action is gentler, returning the sand to rebuild the beaches. Hurricanes and tropical storms from late summer to fall can have dramatic impacts on beach morphology. Beaches are largely devoid of plant growth due to frequent wetting and drying, Figure 5.1. Aerial view of wetlands along Connecticut’s Long Island Sound shore. Figure 5.2. All beaches are not alike: (a) gravel beach (Bay of Fundy, NS); (b) coarse, sandy beach (Cape Cod Bay, MA, with broad sand flats); and (c) broad, fine, sandy beach (GA). a b...