Coastal CommunitiesCoastal Communities II ELEMENTS OF BIODIVERSITY – NATURAL COMMUNITIES

salt marshcordgrass

black needlerush

MeanSea Level

saltwort

uplandvegetation

North Florida Salt Marsh

beachdune

scrubcoastalgrassland

mesic flatwoods

Panhandle Sandy Coast

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AtlanticOcean

coastalstrand

maritimehammock

Peninsula Sandy Coast

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Mean Highwater

redmangrove

blackmangrove

South Florida Mangrove Swamp

Zone in which most tropicalwoody species drop out ofupland and wetland coastal

vegetation

Location ofaerial photoshown below

Coastal uplandMangroveSalt marsh

Zonation is characteristic of coastal vegetation. Successive dune ridges inland from the beach often show a change from pioneering coastal grasses nearest the beach to other types of vegetation, culminating in woody vegetation resembling that found on the mainland. A coastline that has been building seaward allows us to follow how such coastal zonation develops. At Crooked Island West on Tyndall Air Force Base east of Panama City in Bay County, aerial photographs from1980, 1983, and 1986 record a rapidly prograding shoreline that built seaward over 0.2 miles in seven years. At each successive shoreline, a dune ridge was built up above the beach as pioneering dune grasses, such a sea oats (Uniola paniculata) or, in this case, bitter panicgrass (Panicum amarum), trapped sand blown off the beach and grew upward under burial. As a new dune ridge formed in front of the earlier ridge, it protected the earlier ridge from windborne sand and salt spray off the beach, permitting different plants to colonize it and to replace the pioneering species.

By comparing the positions of these ridges (magenta lines) on a current aerial with shorelines on earlier aerials, the dates when each of four ridges on the most recent aerial stood at the shoreline can be identified. In 1987, vegetation on each of the ridges was sampled across transect A–A’ from what was then the shoreline ridge

inland. (The coast has since continued to build seaward as shown on this 2004 aerial.) The first two ridges (1987 and 1986) are covered by the pioneer bitter panicgrass, whereas the inner two (1983 and 1980) are dominated by Gulf bluestem (Schizachyrium maritimum), still a coastal specialist, but a finer grass than bitter panicgrass and one that tolerates only a moderate rate of sand burial. Thus, in our example, bitter panicgrass that presumably formed the 1983 ridge when it was at the shoreline was replaced by bluestem within one to three years of its being protected by a more seaward ridge. Likewise, since the second ridge (1986) has been protected for less than a year by the current shoreline ridge and still has bitter panicgrass, we know that under a year is too short a time for Gulf bluestem to replace bitter panicgrass. And since the 1980 ridge still has Gulf bluestem and has been protected by the third ridge for between three and seven years, we know that that is insufficient time for other vegetation to replace Gulf bluestem.

By piecing together many similar examples along the coast, we can begin to predict how dune vegetation will change and how rapidly these changes will occur once a dune ridge is protected from the coastal stresses of wave erosion, sand burial, and salt spray found at the shoreline.

Changing Coastal Vegetation: Crooked Island West

Coastal Uplands predevelopment currentAcres in Florida >200,000 85,000

Global Rank State RankBeach Dune G3 S2Coastal Berm G3 S2Coastal Dune Lake G2 S1Coastal Grassland G3 S2Coastal Interdunal Swale G3 S2Keys Coastal Rock Barren G1 S1Coastal Rockland Lake G2 S1Coastal Strand G3 S2Maritime Hammock G3 S2

Coastal Wetlands predevelopment currentAcres in Florida ca. 1,059,000 730,000

Global Rank State RankEstuarine Tidal Marsh (Salt Marsh) G5 S4Estuarine Tidal Swamp (Mangrove) G5 S4

Florida Coastal Communities

1987

bitter panicgrass Gulf bluestem

1986 1983 1980

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A t over 3,000 miles (exclusive of the Keys), Florida’s coastline is longer than

that of any other state except Alaska. About two-thirds of it is sandy, high-wave-energy coastline, occupied by dunes and beaches. The low-wave-energy coast, occupied by salt marshes and mangroves, is concentrated in the big bend region where the peninsula curves around to join the panhandle, and at the southern tip of the state. Florida’s long coastline stretches across two climate zones, warm temperate and subtropical, which are reflected in the transition from salt marsh to mangrove vegetation in the vicinity of Tampa and Cape Canaveral. On sandy coasts, the same pioneer grasses on beach dunes range throughout the state; however, more inland dune vegetation also shows a transition to tropical species in about the same area as the mangrove/salt marsh transition. In addition to climate, stable dune vegetation also reflects differences in substrate. Stable dunes on the acid sands of the panhandle support scrub and mesic flatwoods, whereas stable dunes on less acid, shell-plus-quartz sands of the peninsula support coastal strand and maritime hammock.

Panhandle Sandy Coast

Coastal Grassland The coastal grassland community develops when the first dune above the beach is protected from salt spray and sand burial by a new dune ridge. As the beach builds seaward, the pioneer grasses of the beach dune community are replaced by other grasses and forbs of the coastal grassland community. These species do not range along the entire coast but change as one goes southward. The acid sugar sands of the panhandle coastal grasslands are dominated by Gulf bluestem (Schizachyrium maritimum), a grass endemic to the northeast Gulf coast from Florida to Mississippi, whereas a variety of forbs and grasses comprise the coastal grasslands of the peninsula.

Beach Dune On sandy coasts, the beach dune community that occupies the upper beach and first dune is composed of specialized pioneer grasses and forbs, most of which range throughout the state. Sea oats (Uniola paniculata) and bitter panicgrass (Panicum amarum) are the primary dune-building grasses. The upper beach is colonized by the seacoast marshelder (Iva imbricata) and shoreline sea purslane (Sesuvium portulacastrum), often accompanied by the wide ranging runners of railroad vine (Ipomoea pes-caprae ssp. brasiliensis) and beach morning glory (Ipomoea imperati).

Coastal strand is a dense shrubby community found in the transition zone to maritime hammock on quartz sands mixed with shell along both coasts of the peninsula. The shrubs are kept low by salt spray blowing off the water, and they gradually increase in height with distance from the coast until they merge into tree-sized species forming the canopy of maritime hammock. Nearest the coast saw palmetto (Serenoa repens) forms a nearly pure stand with occasional stunted cabbage palms (Sabal palmetto). Further inland shrubs become prominent, including tough buckthorn (Sideroxylon tenax) and Hercules’ club (Zanthoxylum

Salt Marsh Salt marsh consists of vast expanses of either salt marsh cordgrass (Spartina alterniflora) or black needlerush (Juncus roemerianus). Which species predominates depends on the amplitude of the tides. Where the tidal amplitude is greater, as along the extreme northeast coast of Florida, salt marsh cordgrass predominates, since it thrives under longer flooding; where tidal amplitude

Mangrove SwampMangrove swamps are formed by three species of mangrove: red mangrove (Rhizophora mangle) nearest the open water and black mangrove (Avicennia germinans) and white mangrove (Laguncularia racemosa) further inland. Buttonwood (Conocarpus erectus) occurs on the inland edges; it tolerates brackish

clava-herculis) mixed with dwarfed live oak (Quercus virginiana), red bay (Persea borbonia), and cabbage palms, which gradually increase in height inland until they form the canopy of maritime hammock. In the tropical portion of the coast, sea grape (Coccoloba uvifera) is found closest to the coast and like live oak may increase in height to form a canopy of maritime hammock with increasing distance from the coast or with protection from a tall dune. Joining it in the canopy are other tropical tree species, often including gumbo limbo (Bursera simaruba) and white stopper (Eugenia axillaris), among others.

Peninsular Sandy Coast

Coastal Strand and Maritime Hammock

South Florida Mangrove Swamp

is lower, as in most of Florida, black needlerush covers most of the marsh. On higher salinity salt flats, which are seldom flooded, both species are replaced by either the low grasses, saltgrass (Distichlis spicata) and shoregrass (Monanthochloe littoralis), or the succulents, saltwort (Batis maritima) and perennial glasswort (Sarcocornia perennis).

groundwater but not regular inundation. Salt flats are also found in mangrove swamps and are colonized by the same species as they are in salt marsh, along with stunted mangroves. Salt marsh and mangrove swamp form some of the most productive habitats in Florida and are important nurseries for fish and other marine life.

North Florida Salt Marsh

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Carolyn Kindell Ann F. Johnson Gary Schultz Ann F. Johnson

David Moynahan David Moynahan

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