2 Wetland Plant Communities I. Wetland Plant Habitats Wetland plants grow in a variety of climates, from the tropics to polar regions — wherever the water table is high enough, or the standing water is shallow enough, to support them. Each species is adapted to a range of water depths and many do not survive outside of that range for extended periods. For example, Hydrilla verticillata (hydrilla) thrives when fully submerged; Typha angustifolia (narrow-leaved cattail) can grow in water over 1 m in depth, but its leaves are emergent; and others, like Larix laricina, the tamarack tree of northern peatlands, are fully emergent and normally do not grow where water covers the soil sur- face. All rooted wetland plants are adapted to at least periodically saturated substrates where soil oxygen levels are low to non-existent. The terms for different types of wetlands help to pinpoint the differences between wet- land communities and can be defined, at least in part, by the type of vegetation that grows there. For example, swamp denotes a wet area where trees or shrubs dominate the canopy, such as a cypress swamp, while a marsh is dominated by herbaceous species, such as a cat- tail marsh. Names given to some wetland types denote either the source or the chemistry of the water, such as riparian wetland, or salt marsh. Wetlands are recognized as vital ecosystems that support a wide array of unique plants especially adapted to wet conditions. Wetland plants, in turn, support high densities of fish, invertebrates, amphibians, reptiles, mammals, and birds. Wetland conditions such as shallow water, high plant productivity, and anaerobic substrates provide a suitable envi- ronment for important physical, biological, and chemical processes. Because of these processes, wetlands play a vital role in global nutrient and element cycles. Wetlands also provide key hydrologic benefits: flood attenuation, shoreline stabilization, erosion control, groundwater recharge and discharge, and water purification (Mitsch and Gosselink 2000). In addition, they provide economic benefits by supporting fisheries, agriculture, timber, recreation, tourism, transport, water supply, and energy resources such as peat (T.J. Davis 1993). II. Wetland Definitions and Functions The term wetland envelops a wide variety of habitats, from mangroves along tropical shorelines to peatlands that lie just south of the Arctic. The following definitions help iden- tify commonalties among these vastly different ecosystems. L1372 - Chapter 2 04/25/2001 9:27 AM Page 29 © 2001 by CRC Press LLC A. Ecological Definition The determining factor in the wetland environment is water. To a great extent, hydrology determines soil chemistry, topography, and vegetation. All wetlands have water inputs that exceed losses, at least seasonally. It is difficult to say exactly how much water an area must have at any given time in order to be a wetland. Indeed, Cowardin and others (1979) state that a “single, correct, indisputable, and ecologically sound” definition of wetlands does not exist, mostly because the line between wet and dry environments is not easily drawn. Moisture levels vary along a continuum that shifts in time and space. Wetlands may have standing water throughout the year, or only during a portion of the year. Those influenced by tide may have water at each high tide, or only at each spring tide. In all wetlands, the substrate is saturated enough of the time that plants not adapted to saturated conditions cannot survive. Saturated conditions lead to low oxygen (hypoxia) or a lack of oxygen (anaerobiosis or anoxia) in the soil pore spaces. Scarcity of oxygen brings about reducing conditions, in which reduced forms of elements (e.g., nitrogen, manganese, iron, sulfur, and carbon) are present (Gambrell and Patrick 1978). Such substrates are termed hydric soils. Wetland plants have adaptations to waterlogging and hydric soils that allow them to persist. Wetlands, then, are ecosystems in which there is sufficient water to sustain both hydric soils and the plants that are adapted to them. B. Legal Definitions Legal or formal definitions of wetlands have been adopted in a number of countries. In the U.S., a legal definition of wetlands is needed because wetlands are protected areas, regu- lated by government agencies. Wetland definitions help classify areas so that the appro- priate protections or uses can be determined. Many nations have wetland definitions, and each country’s definition tends to focus on the characteristics of that country’s wetlands (Scott and Jones 1995). The international definition adopted by the Ramsar Convention of 1971 (Matthews 1993) is often the basis for the definition used by individual countries. 1. United States Army Corps of Engineers’ Definition In the U.S., wetlands are legally defined by government agencies actively involved in wet- land identification, protection, and the issuance of permits to people who seek to alter wet- lands. The U.S. Army Corps of Engineers and the U.S. Environmental Protection Agency define wetlands as: those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands gen- erally include swamps, marshes, bogs, and similar areas (Federal Interagency Committee for Wetland Delineation 1989). This definition is used for the delineation of wetlands throughout the U.S. Disputes con- cerning wetland boundaries often arise because wetlands do not have distinct edges. Three components of the wetland ecosystem are taken into consideration by the U.S. definition: hydrology, soil, and vegetation (see Chapter 10, Wetland Plants as Biological Indicators). Specific indicators of all three must be present during some part of the grow- ing season for an area to be a wetland, unless the site has been significantly altered. Indicators of wetland hydrology include the presence of standing or flowing water or tides, but water may also be below the soil surface in a wetland. Secondary indicators of L1372 - Chapter 2 04/25/2001 9:27 AM Page 30 © 2001 by CRC Press LLC water level may also be used to establish wetland hydrology, such as water marks, drift lines, debris lodged in trees or elsewhere, and layers of sediment that form a crust on the soil surface. Hydric soils develop under low oxygen conditions that bring about diagnos- tic soil colors, textures, or odors. Other soil indicators include partially decomposed plant material in the soil profile (as in peatlands) or decomposing plant litter at the surface of the soil profile. The dominance of wetland vegetation (and the absence or rarity of upland veg- etation) indicates a wetland. 2. U.S. Fish and Wildlife Classification of Wetlands For the purpose of wetland and deepwater habitat classification, the U.S. Fish and Wildlife Service (Cowardin et al. 1979) defined wetlands as: … lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. For purposes of this classification, wetlands must have one or more of the following three attributes: (1) at least periodically, the land supports predominantly hydrophytes; (2) the substrate is predomi- nantly undrained hydric soil; and (3) the substrate is nonsoil and is saturated with water or covered by shallow water at some time during the growing season of each year. This definition is the basis for a detailed classification of wetlands (the Cowardin system, 1979) that was a first step in compiling an inventory of all U.S. wetlands (the National Wetlands Inventory). 3. International Definition In 1971, an international convention on wetlands was held in Ramsar, Iran by the International Union for the Conservation of Nature and Natural Resources (IUCN). An international treaty on wetlands, the Convention on Wetlands of International Importance Especially as Waterfowl Habitat, also known as the Ramsar Convention, was signed there. It “provided the framework for international cooperation for the conservation and wise use of wetlands and their resources” (Matthews 1993). Under the Ramsar Convention wet- lands are defined as: … areas of marsh, fen, peatland or water, whether natural or artificial, permanent or tem- porary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six meters. In addition, wetlands “may incorporate riparian and coastal zones adjacent to the wet- lands, and islands or bodies of marine water deeper than six meters at low tide lying within the wetlands.” The Ramsar Convention definition of wetlands is broader than the U.S. Army Corps of Engineers’ definition as it includes coral reefs and other deeper water habitats. The inclu- sion of more habitat types in the definition allows the convention to protect a greater area. All signatory nations agree to designate at least one site for inclusion on the Ramsar List. Inclusion confers international recognition on a site and obliges the government to main- tain and protect the wetland. As of February 2000, there were 118 contracting parties with 1,016 sites on the Ramsar List for a total area of over 72.8 million ha (Ramsar Convention Bureau 2000). The Ramsar Convention emphasizes the “wise use” and “sustainable development” of wetlands rather than conservation. They define wise use as the “sustainable utilization [of wetlands] for the benefit of mankind in a way compatible with the maintenance of the L1372 - Chapter 2 04/25/2001 9:27 AM Page 31 © 2001 by CRC Press LLC natural properties of the ecosystem.” Sustainable utilization of a wetland is defined as “human use of a wetland so that it may yield the greatest continuous benefit to present generations while maintaining its potential to meet the needs and aspirations of future generations” (T.J. Davis 1993). In order to use a wetland wisely, a thorough understanding of its functions within the landscape is essential. C. Functions of Wetlands Whether wetlands are bordered by upland forest, desert, tundra, agricultural land, urban areas, or ocean, they often perform similar roles, or functions, within the broader land- scape. All wetland functions are related to the presence, quantity, quality, and movement of water in wetlands (Carter et al. 1979). Functions are linked to the self-maintenance of the wetland and its relationship to its surroundings (Mitsch and Gosselink 2000). The func- tions of wetlands can be categorized into three main categories: hydrology, biogeochem- istry, and habitat (Walbridge 1993). Wetland functions do not necessarily affect humans directly. Another term, values, refers to the benefits society derives from wetlands. Wetland values are closely tied to functions (Table 2.1). 1. Hydrology Hydrologic functions of wetlands include the recharge and discharge of ground water supplies, floodwater conveyance and storage, and shoreline and erosion protection. TABLE 2.1 Functions and Values Commonly Attributed to Wetlands Function Societal Value Hydrology Flood mitigation Groundwater recharge Shoreline protection Biogeochemistry Sediment deposition Improved water quality Phosphorus sorption Nitrification Denitrification Sulfate reduction Nutrient uptake Sorption of metals Carbon storage Global climate mitigation Methane production Plant and animal habitat Timber production Agricultural crops (rice, cranberries, etc.) Animal pelts (furs and skins) Commercial fish/shellfish production Recreational hunting and fishing Adapted from Walbridge 1993. L1372 - Chapter 2 04/25/2001 9:27 AM Page 32 © 2001 by CRC Press LLC a. Groundwater Supply Groundwater may move into a wetland via springs or seeps (groundwater discharge) and water from the wetland may seep into the groundwater (groundwater recharge). Groundwater can be recharged from depressional wetlands if the water level in the wet- land is above the water table of the surrounding soil. Recharge is important for replenish- ing aquifers for water supply. At some sites, both recharge and discharge occur. For exam- ple, in Florida cypress ponds, the water level is continuous with the water table of the surrounding landscape. When the water table rises due to rainfall, groundwater moves into the cypress pond. In dry periods, the water movement is reversed, and the aquifer is recharged (Ewel 1990a). b. Flood Control Wetlands can temporarily store excess water and release it slowly over time, thus buffer- ing the impact of floods. Intact and undeveloped riparian wetlands can prevent damaging floods along rivers (Sather and Smith 1984). Depressional wetlands such as cypress ponds or prairie potholes have the capacity to receive and store at least twice as much water as a site filled with soil (Ewel 1990a). Some wetlands are not able to store excess water. If wet- lands are impounded in order to store more floodwater than they normally would, signif- icant changes in the plant community can result (Thibodeau and Nickerson 1985). c. Erosion and Shoreline Damage Reduction Wetlands along rivers, lakes, and seafronts can protect the shoreline by absorbing the energy of waves and currents. Wetlands along shorelines are dynamic systems, generally reaching equilibrium between accretion and erosion of substrate. Structures used for shoreline protection, such as bulkheads or jetties, can destroy the shoreline habitat by interrupting this equilibrium. These structures can also channel sediment into navigable waterways, where the cost of dredging is added to the cost of shoreline protection (Adamus and Stockwell 1983). Mangroves along tropical shorelines provide a good exam- ple of the erosion protection that wetlands can provide. Their extensive roots help stabilize sediments and prevent wave damage to inland areas (Odum and McIvor 1990). In China, wetlands have been created for shoreline reclamation and stabilization using vast plantings of Spartina alterniflora (cordgrass [Chung 1993]). 2. Biogeochemistry A number of important biogeochemical processes are favored in wetlands due to shallow water (which maximizes the sediment-to-water interface), high primary productivity, the presence of both aerobic and anaerobic sediments, and the accumulation of litter (Mitsch and Gosselink 2000). These conditions often lead to a natural cleansing of the water that flows into wetlands. Incoming suspended solids settle from the water column due to the reduced water velocity found in wetlands (Johnston et al. 1984; Fennessy et al. 1994b). Materials associated with solids, such as phosphorus, are also removed from the water col- umn in wetlands (Johnston 1991; Mitsch et al. 1995). Nitrogen is transformed through microbial processes (e.g., nitrification followed by denitrification; Faulkner and Richardson 1989) which require the presence of both aerobic and anaerobic substrates. Plant uptake and plant tissue accumulation can also remove nitrogen and phosphorus from the water; however, this process can be reversed when plants die back after the grow- ing season (Howarth and Fisher 1976; Richardson 1985; Peverly 1985). Wetlands also play a role in the global cycling of sulfur and carbon as their anaerobic forms are produced under wetland conditions (see Chapter 3, Section III.A.1, Reduced Forms of Elements). L1372 - Chapter 2 04/25/2001 9:27 AM Page 33 © 2001 by CRC Press LLC The capacity of wetlands to purify water is one of the most important societal values wetlands provide. Water quality improvements within wetlands are well documented (Engler and Patrick 1974; Odum et al. 1977; Mitsch et al. 1979; Dierberg and Brezonik 1983; Nichols 1983; Kadlec 1987; Knight et al. 1987; Brodrick et al. 1988; Mitsch 1992; Mitsch et al. 1995; Cronk 1996; Fennessy and Cronk 1997) and both natural and constructed wet- lands are used worldwide to treat wastewater from industrial, agricultural, and domestic sources (Kadlec and Knight 1996; see Chapter 9, Section II, Treatment Wetlands). 3. Habitat a. Wildlife and Fish Habitat Because many wetlands are highly productive ecosystems, they support a large number of fish and wildlife species. Some animals, such as many fish, reptiles, and amphibians, depend exclusively on wetland habitats. Others utilize wetlands for only short periods of their life cycles (breeding, resting grounds) and some use wetlands as a source of food and water. Wetlands provide a habitat for many endangered and threatened animal species such as whooping cranes (Grus americana; U.S. Fish and Wildlife Service 1980), wood storks (Mycteria americana), crocodiles (Crocodylus acutus), snail kites (Rostrhamus socia- bilis; U.S. National Park Service 1997), and Florida panthers (Puma concolor coryi; Maehr 1997). Hunters use wetland areas extensively for both waterfowl and deer, and their activ- ities provide an economic value to the wildlife function of wetlands. Many animals such as muskrats, beavers, mink, and alligator are harvested for the fur and leather industries, worth millions of dollars annually. Both commercial and sports fisheries depend on the fish and shellfish of wetlands. b. Plant Habitat Wetland plant communities are among the most highly productive ecosystems in the world (Mitsch and Gosselink 2000). The production of biomass and the export of organic carbon to downstream areas make wetlands an integral part of a landscape’s food web. The high usage of wetlands by wildlife attests to wetland plants’ importance and diversity. Wetland plant products such as timber from bottomland swamps, peat from bogs, and many plant food products such as Oryza sativa (rice), Trapa bispinosa (water chestnut), and various species of Vaccinium (blueberries and cranberries) are harvested throughout the world. In many areas, farm animals graze wetland plants. Wetland plant habitat is threatened by changes in wetland hydrology, eutrophication, the invasion of exotic plants, and other human-induced disturbances such as agriculture and development (Wisheu and Keddy 1994). Although many wetland plants are listed by the U.S. Fish and Wildlife Service as rare or endangered, wetland management plans rarely mention the conservation of rare species (Lovett-Doust and Lovett-Doust 1995; see Chapter 1, Table 1.3). III. Broad Types of Wetland Plant Communities One of the challenges wetland ecologists face is classifying wetlands so that plant commu- nities, soil types, and hydrologic influences can be described, managed, mapped, or quan- tified. The variety of wetland types is enormous, and all wetland classifications must impose subjective boundaries on types. The sources and amounts of water vary over a wide range even within the same type of wetland. In addition, wetlands are found along succes- sional gradients, further complicating their classification. Nonetheless, classification of L1372 - Chapter 2 04/25/2001 9:27 AM Page 34 © 2001 by CRC Press LLC wetlands is useful in order to describe their characteristics and manage them effectively (Cowardin et al. 1979). Several wetland classification schemes have been used, some for specific regions, coun- tries, or states, and some for certain types of wetlands, such as peatlands (Shaw and Fredine 1956; Taylor 1959; Bellamy 1968; Stewart and Kantrud 1971; Golet and Larson 1974; Cowardin et al. 1979; Beadle 1981; Zoltai 1983). Internationally, a number of nations have classified and inventoried their wetlands, including Canada, Greece, Indonesia, and South Africa. Some of these countries have used the Ramsar definition as a starting point and adapted it to local conditions. For example, Canada’s classification system has five wetland classes and 70 wetland forms, half of which are types of northern peatlands. Indonesia has classified wetlands into six mangrove forest types and eight freshwater forested wetland types (Scott and Jones 1995). In the U.S., the first well-known official wetland classification was published by the U.S. Fish and Wildlife Service in 1956 (Shaw and Fredine 1956). In this publication, known as Circular 39, wetlands were categorized into four broad types: inland fresh areas, inland saline areas, coastal fresh areas, and coastal saline areas. Each of these was further divided for a total of 20 wetland types. This classification scheme was influential in the beginning of federal wetland protection. Other classifications were statewide and were based on regional wetland characteristics. In order to better define and inventory the wetlands of the U.S., the U.S. Fish and Wildlife Service developed a classification of wetlands and deepwater habitats based on the geologic and hydrologic origins of wetlands (Cowardin et al. 1979). This classification is beneficial because it eliminates the reliance on regional terms that may be meaningless in other parts of the country. In the Cowardin classification scheme, the major systems of wetland and deepwater habitat types are marine, estuarine, lacustrine, palustrine, and river- ine. Systems are wetlands that share similar hydrologic, geomorphologic, chemical, or bio- logical factors. The Cowardin system includes deepwater habitats (e.g., coral reefs), and those where plants do not grow, such as coastal sand flats or rocky shores. A more recently developed classification scheme, called the hydrogeomorphic (HGM) setting of a wetland, is based on three parameters: the wetland’s geomorphic setting within the landscape (i.e., riverine, depressional, lacustrine fringe), its water source, and the internal movement of water within the wetland, known as its hydrodynamics. As a classification system, the HGM approach emphasizes the topographic setting and the hydrology of the wetland that in turn affect its functions (Brinson 1993a). In this scheme, the presence of vegetation is seen as a result of the long-term interaction of climate and landscape position that also control wetland hydrology. Alternatively, an approach based on the hydrogeologic setting (HGS) refers to the fac- tors, both regional and local, that drive wetland hydrology and chemistry. It places an emphasis on the surface and subsurface features of the landscape that cause water flow into wetlands, thus determining the quantity and quality of water that a wetland receives (Bedford 1999). Winter (1992) defined the HGS in terms of surface relief and slope, soil thickness and permeability, and the stratigraphy, composition, and hydraulic conductivity of the underlying geologic materials. He used these parameters to classify sites into one of 24 “type settings” based on unique combinations of physiography and climate. This framework has a landscape basis and has been proposed for use in classifying wetlands for research into their diversity and ecological functions. For the purposes of this book, we describe broad types of systems where wetland plants grow. We have categorized wetlands into three major wetland plant communities: (1) marshes, where herbaceous species dominate; (2) forested wetlands, where trees or L1372 - Chapter 2 04/25/2001 9:27 AM Page 35 © 2001 by CRC Press LLC shrubs dominate; and (3) peatlands, where the decomposition of plant matter is slow enough to allow peat to accumulate. Within these three categories, we further divide our description of plant communities based on hydrology, salinity, and pH. A. Marshes Marshes are dominated by herbaceous species which can include emergent, floating- leaved, floating, and submerged species. The term marsh covers a broad range of habitat types, and marshes can be found around the world in both inland and coastal areas. Further classification is based on hydrology and specific herbaceous type. Many names for marshes exist due to the numerous possible local plant associations in marshes. For exam- ple, in the state of Florida, a marsh can be classified as a water lily marsh, a cattail marsh, a flag marsh, or a sawgrass marsh (after the dominant plant), or a submersed marsh or wet prairie (after the community type; Kushlan 1990). Coastal marshes and inland marshes are discussed in more detail below. 1. Coastal Marshes a. Salt Marshes Salt marshes occur in coastal areas and are usually protected from direct wave action by barrier islands, or because they are located within bays or estuaries, or along tidal rivers (Figure 2.1). However, some are in direct contact with ocean waves on low-energy coast- lines such as the Gulf of Mexico coast in west Florida and parts of Louisiana, the north Norfolk coast of Britain, and the coast of the Netherlands (Pomeroy and Wiegert 1981). Most salt marshes are found north and south of the tropics. In the tropics, mangroves are able to outcompete marsh plants (Kangas and Lugo 1990), although salt marshes do per- sist inland from mangroves in tropical (northern) Australia (Finlayson and Von Oertzen 1993) and alongside mangroves in some coastal areas of Mexico (Olmsted 1993). Salt marshes occur as far north as the subarctic and are particularly extensive around the Hudson and James Bays of Canada (approximately 300,000 km 2 ; Glooschenko et al. 1993). FIGURE 2.1 Salt marsh in Cape Cod, Massachusetts with Spartina patens (salt marsh hay) in the foreground and S. alterniflora (cordgrass) near the tidal creek. (Photo by H. Crowell.) L1372 - Chapter 2 04/25/2001 9:27 AM Page 36 © 2001 by CRC Press LLC The plant communities of salt marshes are subjected to daily and seasonal water level fluctuations due to tides, and to variations in freshwater inputs from overland runoff. In addition, plants are adapted to low soil oxygen levels that can lead to high levels of sulfide (Valiela and Teal 1974). Some salt marsh plants are able to withstand salt concentrations in the soil pore water that are sometimes higher than that of seawater (i.e., 35 ppt) due to the deposition of salt and evaporation (Wijte and Gallagher 1996a). In North America, some of the major remaining areas of salt marshes are on the Atlantic coast and along the Gulf of Mexico. Along the northern Atlantic shore, the coasts of Labrador, Newfoundland, and Nova Scotia harbor salt marshes in river deltas and where the wave energy is low (0 to 2 m amplitude; Roberts and Robertson 1986). South of this region, salt marshes have been divided into three major types (Chapman 1974; Mitsch et al. 1994): 1. The Bay of Fundy marshes in Canada: These marshes are influenced hydrologi- cally by rivers and a high tidal range (up to 11 m; Gordon and Cranford 1994) that erodes the surrounding rocks. The substrate is predominantly red silt. 2. New England marshes (from Maine to New Jersey): These marshes were formed on marine sediments and marsh peat without as much upland erosion as in the Bay of Fundy marshes. 3. Coastal Plain marshes: These marshes extend from New Jersey south along the Atlantic and along the Gulf of Mexico coast to Texas. The tidal range is smaller and the inflow of silt from the coastal plain is high. Included among these are the Mississippi River delta wetlands, which are the largest salt marshes in the U.S. All three of these salt marsh types are dominated by Spartina alterniflora (Figure 2.2). S. alterniflora is a perennial grass that usually occurs along the seaward edge of salt marshes (Metcalfe et al. 1986) and can grow in water salinities as high as 60 ppt (Wijte and FIGURE 2.2 Spartina alterniflora (cordgrass), the dominant plant of many U.S. east coast and Gulf of Mexico salt marshes. (Photo by H. Crowell.) L1372 - Chapter 2 04/25/2001 9:27 AM Page 37 © 2001 by CRC Press LLC Gallagher 1996a). Two forms of S. alterniflora often coexist within the same marsh: the tall and short forms. The tall form (1 to 3 m) grows along the banks of tidal creeks, in the low- est part of the marsh, closest to the sea. The short form (10 to 80 cm) grows inland from there (Valiela et al. 1978; Anderson and Treshow 1980; Niering and Warren 1980). More stressful conditions in the inland area of the low marsh, such as nitrogen limitation (Valiela and Teal 1974; Gallagher 1975), high salinity (Anderson and Treshow 1980), and low soil oxygen levels (Howes et al. 1981), may cause the height difference (see Chapter 4, Case Study 4.A, Factors Controlling the Growth Form of Spartina alterniflora). Salt marshes provide a striking example of plant species zonation in response to envi- ronmental variation, with different species occurring at different marsh elevations. Each species’ habitat can be explained by its tolerance to salinity levels, tidal regime, soil oxy- gen availability, sulfur levels, or other factors (Partridge and Wilson 1987). In many east- ern U.S. and Gulf coast salt marshes, a zone of Spartina patens (salt marsh hay) is located inland from the zone of both forms of S. alterniflora (Bertness and Ellison 1987; Gordon and Cranford 1994). S. patens may dominate in the better drained and less saline areas of salt marshes because it outcompetes S. alterniflora in those sites (Bertness and Ellison 1987; Bertness 1991a, b). Although east coast salt marshes of the U.S. appear to be monospecific within each of these zones, other salt marsh species are present in smaller numbers, such as Juncus gerardii (rush), Distichlis spicata (spike grass), and Salicornia europaea (glasswort; Bertness and Ellison 1987). On the Pacific coast of the U.S. and Canada, salt marshes are less extensive than in the east, mostly because the geophysical conditions are not suitable for salt marsh formation. Crustal rise has resulted in shoreline emergence and a coastline with cliffs and few wide flat river deltas and estuaries. The majority of Pacific coast salt marshes that did exist have been filled for development (over 90% in some areas; Dahl and Johnson 1991; Chambers et al. 1994). Salt marshes still exist in estuaries or protected bays like Tijuana Estuary near San Diego (Zedler 1977), in northern San Francisco Bay (Mahall and Park 1976), Tomales Bay north of San Francisco (Chambers et al. 1994), Nehalem Bay in northern Oregon (Eilers 1979), Puget Sound in Washington (Burg et al. 1980), at the head of fjords and on the Queen Charlotte Islands in British Columbia (Glooschenko et al. 1993), and in Cook Inlet near Anchorage, Alaska (Vince and Snow 1984). The plant communities of western salt marshes tend to be more diverse than Atlantic coast and Gulf of Mexico marshes. Like Atlantic salt marshes, many west coast salt marshes are dominated by grasses. For example, Spartina foliosa dominates some southern California marshes (Zedler 1977) as well as marshes near San Francisco (Mahall and Park 1976). Other northern California marshes are dominated by Distichlis spicata (Chambers et al. 1994), while Salicornia virginica (glasswort) is a dominant species in marshes of both northern and southern California (Callaway et al. 1990; Zedler 1993; Chambers et al. 1994). In Oregon, Washington, and British Columbia, the sedge, Carex lyngbyei, dominates salt marshes (Eilers 1979; Burg et al. 1980; Glooschenko et al. 1993). Alaskan salt marshes are dominated by the grass, Puccinellia phryganodes, and by various species of Carex (Jefferies 1977; Vince and Snow 1984). Diversity tends to be highest in better drained and less saline locations (MacDonald and Barbour 1974; Vince and Snow 1984; Chambers et al. 1994). In western and northern Europe, salt marshes are found along the Atlantic coasts of Spain, Portugal, France, and Ireland, and along the North Sea and the Baltic Sea. In south- ern Europe, salt marshes are located within the watershed of the Mediterranean Sea and in the Rhone River delta (the Camargue; Chapman 1974). Mediterranean salt marshes also fringe northern Africa along the Tunisian, Moroccan, and Algerian coasts (Britton and Crivelli 1993). The seaward portions of European salt marshes are often tidal mudflats, L1372 - Chapter 2 04/25/2001 9:27 AM Page 38 © 2001 by CRC Press LLC [...]... on hummocks between the floating peat mat and more solid ground (Ebersole Center, Jackson Lake in southwestern Michigan) (Photo by H Crowell.) © 20 01 by CRC Press LLC L13 72 - Chapter 2 04 /25 /20 01 9 :28 AM Page 59 Summary Wetlands are defined using three major components: hydrology, soils, and plants The hydrology of wetlands varies daily in coastal wetlands, and seasonally in others There must be sufficient... flooded and therefore better drained (Hodges 1997) © 20 01 by CRC Press LLC L13 72 - Chapter 2 04 /25 /20 01 9 :28 AM Page 49 Southern bottomland hardwood forests are found in both major and minor watersheds from the Atlantic coast to eastern Texas and Oklahoma and as far north as the Ohio and Wabash Rivers Some of the largest floodplains in which bottomland forests grow are along the lower Mississippi and its... by sedges, and the term fen is used More detailed categories of fens according to pH are intermediate fen (pH 5 .2 to 6.4), transitional rich fen (pH 5.8 to FIGURE 2. 17 Three classifications of peatlands according to pH value (names and their pH ranges are from [a] Sjors 1950, [b] Bellamy 1968, and [c] Crum 19 92) © 20 01 by CRC Press LLC L13 72 - Chapter 2 04 /25 /20 01 9 :28 AM Page 54 FIGURE 2. 18 Parnassia... The size and depth of littoral wetlands shift with changes in water level due to precipitation or changes in drainage or runoff © 20 01 by CRC Press LLC L13 72 - Chapter 2 04 /25 /20 01 9 :28 AM Page 42 Lacustrine wetlands are located around the world, along the edges of both small and large lakes Most of the world’s lakes are small with a high ratio of lacustrine marsh area to open water (Wetzel and Hough... 23 to 24 ˚C (Tomlinson 1986; Rutzler and Feller, 1996; Figure 2. 10) and they cover 17 to 24 million ha worldwide (Field 1995; Ramsar Convention Bureau 20 00) Mangroves occupy the same niche in the tropics that salt marshes occupy to the north and south Outside of the tropics, frost limits their establishment and causes periodic diebacks (Kangas and Lugo 1990) © 20 01 by CRC Press LLC L13 72 - Chapter 2. .. peat-filled valleys between existing lakes, and glacially formed basins (Kushlan 1990; Galatowitsch and van der Valk 1994) Depressional wetlands are found worldwide, at all latitudes, and may be forested wetlands, marshes, or peatlands (forested depressional wetlands and peatlands are discussed below) Examples of depressional marshes within the U.S and Canada include prairie potholes, playas, and vernal... playas, and vernal pools © 20 01 by CRC Press LLC L13 72 - Chapter 2 04 /25 /20 01 9 :28 AM Page 43 FIGURE 2. 7 Riverine marsh along the upper Mississippi River, Wisconsin (Photo by H Crowell.) One extensive region of depressional wetlands is found in the prairie pothole region of Iowa, Minnesota, North and South Dakota in the U.S., and Alberta, Saskatchewan, and Manitoba in Canada (see Chapter 9, Case Study 9.C,... Crowell.) © 20 01 by CRC Press LLC L13 72 - Chapter 2 04 /25 /20 01 9 :28 AM Page 58 FIGURE 2. 24 Andromeda glaucophylla (bog rosemary) usually grows in the wetter portions of floating mats, closer to the water than other Ericaceae (Miner Lake in southwestern Michigan) (Photo by H Crowell.) FIGURE 2. 25 Larix laricina (tamarack) is a deciduous gymnosperm whose needles turn yellow and drop each fall and grow back... (including Alaska) has more than 26 million ha of forested wetlands (Dahl and Johnson 1991; Hall et al 1994) Like marshes, forested wetlands can be further categorized by hydrology and dominant plant species We have divided this section into two major types: coastal and inland forested wetlands 1 Coastal Forested Wetlands: Mangrove Swamps Mangrove swamps are the only forested wetlands found along coastlines... Canada, Russia, and Scandinavia, peatlands may be vast, extending for thousands of hectares Canada has approximately one third of the world’s peatlands, or 1 12 million ha (88% of Canada’s wetlands are peatlands; Glooschenko et al 1993; Rubec 1994) Over 20 0 million ha of peatlands are found in the eastern hemisphere, in northern Russia, Eastern Europe, Scandinavia, the United Kingdom, and Ireland (Mitsch . dominance of wetland vegetation (and the absence or rarity of upland veg- etation) indicates a wetland. 2. U.S. Fish and Wildlife Classification of Wetlands For the purpose of wetland and deepwater. combinations (Finlayson and Von Oertzen 1993). 2. Inland Forested Wetlands Inland forested wetlands are referred to as either basin wetlands or riverine wetlands, according to their location in the landscape and. herbaceous species dominate; (2) forested wetlands, where trees or L13 72 - Chapter 2 04 /25 /20 01 9 :27 AM Page 35 © 20 01 by CRC Press LLC shrubs dominate; and (3) peatlands, where the decomposition