Everglades Ecosystems



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The Everglades is a low, flat plain shaped by the action of water and weather.Though Everglades National Park is often characterized as a water marsh, several very distinct habitats exist within its boundaries.




Modified from National Park System and Southt Florida Water Management District

Everglades Water FlowSlow and rain-driven, the natural cycle of freshwater circulation historically built up in shallow Lake Okeechobee. It averages 12 feet (3.7 meters) deep and covers 730 square miles (1890 square kilometers). Thus began the flow of the wide, shallow "River of Grass." Fifty miles (80 km) wide in places, one to three feet (0.3 to 0.9 meters) deep in the slough's center but only 6 inches (15 cm) deep elsewhere, it flowed south 100 feet (30 meters) per day across Everglades sawgrass toward mangrove estuaries of the Gulf of Mexico. A six-month dry season followed.

Everglades plants and animals are adapted to alternating wet and dry seasons. Water cycle disruptions ruin crucial feeding and nesting conditions.

During the dry season (December to April), water levels gradually drop. Fish migrate to deeper pools. Birds, alligators, and other predators concentrate around the pools to feed on a varied menu of fish, amphibians, and reptiles. This abundant food source is vital to many wading birds who are nesting during the dry season.

In May, spring thunderstorms signal the beginning of the wet season. A winter landscape dotted with pools of water yields to a summer landscape almost completely covered with water. Wildlife disperses throughout the park. Insects, fish, and alligators repopulate the 'glades, thus replenishing the food chain. By December, the rains cease and the dry cycle begins again.

Originally, the Everglades water flow started with rainfall accumulating in central Florida. Water slowly flowed through the meandering Kissimmee River to Lake Okeechobee. During this process, water was gradually purified. From Lake Okeechobee, the water moved slowly south toward Florida Bay through the Everglades. During this course, the clean water would:

  • hydrologic cyclerecharge the Biscayne Aquifer
  • supply nutrients and oxygen for the Everglades vegetation
  • maintain a supply of freshwater for fish production
  • serve as a good source for migratory birds
  • maintain the food chain
  • reduce risk of fire
  • maintain surface and ground water pressures to reduce salt water intrusion
  • maintain a natural evaporation-transpiration cycle

Slight changes in elevation (only inches), water salinity, and soil create entirely different landscapes, each with its own community of plants and animals.

The Everglades is a low, flat plain shaped by the action of water and weather. In the summer wet season it is a wide, grassy river. In the winter season the edge of the slough is a dry grassland. Though Everglades National Park is often characterized as a water marsh, several very distinct habitats exist within its boundaries.

Marine/Estuarine

Between the southern edge of the Everglades and the Florida Keys lies a large, shallow, subtropical estuary called Florida Bay. The triangular-shaped estuary, with about 2,000 square kilometers, is the largest estuary in Florida and most of it is the largest body of water within the Everglades National Park. Exposed at low tide, the mud flats of Florida Bay provide a valuable feeding area for a number of birds. Plants, such as turtle grass, horned pondweed, seagrass, and manatee grass, stabilize the mud flats. A number of different species of algae also live there. Because its average depth is only about three feet, sunlight can readily reach the bottom and support the growth of seagrass beds. Seagrass beds serve as nursery areas, feeding grounds, and refuges for many species. These grass beds are an excellent habitat for a wide variety of fish and shellfish. The hard bottom areas of Florida Bay are home to a diversity of corals and sponges. The bay is also the home of wildlife, including dolphins, manatees, American crocodiles, bald eagles, ospreys, roseate spoonbills, and many wading birds.

Until recently, this subtropical estuary was noted for its clear, warm waters, lush seagrass beds and outstanding fishing. However, starting in the late 1980s, dramatic changes in the ecology of Florida Bay became evident. These changes included the widespread death of seagrass beds, turbid water associated with this die-off, large and sustained blooms of algae, and population reductions in pink shrimp, sponges, lobster, recreational game fish, and wading birds.

Recognizing Florida Bay's ecological changes, the state of Florida and the federal government made a commitment to improve environmental management in order to restore the bay toward a more natural state.

The seagrasses are an important part of a healthy ecosystem. According to Dwight F. Davis, Mote Marine Laboratory Volunteer, "These meadows of waving vegetation are real grasses as opposed to seaweeds which lack a vascular system and cannot draw nutrition from the substrate. Seagrasses were originally land based but adapted over time to a marine environment. "

"Grass beds in Southwest Florida consist of mostly broad-bladed turtle grass and finer leafed manatee grass and shoal grass, all dependent on sunlight for photosynthesis. They were once found in 30 feet or deeper and were more extensive than they are today. Dredging and filling, together with increased water turbidity from fertilizer and pollutant laden runoff, and scarring from boat keels and propellers have greatly reduced this habitat, especially in the bays. "

"For thousands of marine organisms the seagrass is an ideal environment. It is a place to hide, a place to feed, a place to breed. The basic foodstuff can be the living grass itself, eaten by turtles which literally crop it, by manatees that grub it out roots and all, and by many nibbling animals... parrot-fishes, filefishes, halfbeaks, sea urchins, certain snails and more. Most creatures make their living by scraping the rich epiphytic growths from the tips of the seagrasses, especially turtle grass. Conchs graze here as do pinfish, sheepshead, and many immature fishes whose diets may also include tiny crustacea isopods and shrimps and many larval forms."

"Seagrasses are fast growing and cast off enormous quantities of organic matter which extends the food web far beyond the seagrass bed itself. Bacteria and fungi break down leaf material which contributes to the soft sediments containing high food value for many invertebrate and vertebrate animals. Mullet, for example, can more easily digest the organic matter in detritus(decomposed plant and animal material) than the cellulose in seagrass blades."

"Finally, the seagrass meadows are periodically cruised by large predators rays and nurse sharks feeding on marine snails and crabs; bottlenose dolphin feeding on mullet; and seasonally, other fishes such as tarpon taking sand perch on their way to close-in spawning grounds. "

Mangroves
Mangrove forests are found in the coastal channels and winding rivers around the tip of South Florida. Red Mangroves (
Rhizaphora Mangle), White Mangroves (Laguncularia racemosa), Black Mangroves (Avicennia germinans) and Green Buttonwood (Conocarpus erectus) in the Everglades ecosystems where freshwater from the Everglades mixes with saltwater.

The red mangroves are found in the saltiest region where the open water first meets the land. Red mangroves stand on stilts of roots arching out and down from the trunk.. These prop roots send up a new trunk wherever they touch ground, creating an impenetrable network along the shoreline. There the leaves fall into the calm waters, settle to the bottom and decay to slowly build new land. This muck in between the prop roots of the mangroves contains no oxygen (anaerobic) so the tree extends roots from the branches that are alternately covered and uncovered during the tidal cycle. These roots breath to supply the tree with oxygen when they are in the air and collect nutrients from the sea water when they are exposed. The roots are a platform for oysters and other shellfish filter feeders, as well as many types of algae. As bacteria, fungus, protozoans, or nematodes consume these, a byproduct called detritus is formed. Detritus is an important food source for shrimp, lobsters, crabs, mollusks, worms, and small fish. These in turn are eaten by larger fish and many other species. Juveniles of many species spend a least part of their life cycle sheltered by the prop root systems of the red mangrove. Red mangroves grow to a height of 30 feet in 20 to 30 years. They are used for cabinetry, posts and pilings, shipbuildings and wharves. leaves are a tobacco substitue and fruits are eaten by Seminoles in hard times. Bark provids tannin for furniture stains.

Red mangrove Seedlings in the Mud of Florida Bay Aerial of Mangrove Islands in Florida Bay

Behind the red mangroves at a slightly higher elevation between high and low water marks are the black mangroves. Their roots form a dense mat to under the muck to provide support for the canopy. In order to breath, they send up thin vertical foot long roots out of the soil in order to breath (pneumataphores). They have darker foliage and can grow to heights of 70 feet. They are used for tools, carpentry, construction and posts where a heavy hard wood is required. Flowers provide honey.

Still further up the slope and in brackish water are the white mangroves (to 40 feet) and the green buttonwoods (to 20 feet). Without "breather" roots, they must establish themselves in firmer soil above the tidal lines. White mangroves are used foro carpentry, tool handles and the bark is used to tanning. Green buttonwoods are used for maritime construction of boats and barges, crossties and fences and other underground uses. The plant is often used as an ornamental shrub.

This estuary system is a valuable nursery for shrimp and fish. During the dry months, wading birds congregate here to feed. Many bird species nest in the mangrove trees.

Coastal Prairie

Coastal prairies are found between the tidal mud flats of Florida Bay and dry land in the coast in areas that have been damaged by hurricanes. When a hurricane blows through it topples most of the trees in an area and covers the area in salty silt from the ocean. The result is a slightly raised area of land with highly saline, dry soil and few living trees. The age of the prairie can be approximated by the number of dead snags and live buttonwood. The older the area the fewer the snags and more regrowth of Buttonwood. The snags provide places for epiphytes such as orchids and air plants to grow. The dry, highly saline soil severely limits the plants which are able to grow in the area. A dense mat of vine-like fleshy herbs such as Pickelweed, Glasswort and Saltwort, cover the prairie. This no more than three foot deep maze of plants provides excellent cover for a variety of small mammals which are regularly seen along the fringes of the prairie at dusk and dawn.

Freshwater Marl Prairie
Bordering the deeper sloughs are large prairies with marl sediments, a calcareous material that settles on the limestone. The marl allows slow seepage of the water but not drainage. Though the sawgrass is not as tall and the water is not as deep, freshwater marl prairies look a lot like freshwater sloughs.

Aerial view of the Prarie Fresh Water Prarie and Hammock

Freshwater Slough
The slough is the deeper and faster-flowing center of a broad marshy river. This "fast" flow moves at a leisurely pace of 100 feet (30 meters) per day. Dotted with tree-islands called hammocks or heads, this vast landscape channels life-giving waters from north to south. Everglades National Park contains two distinct sloughs: Shark River Slough, the "river of grass;" and Taylor Slough, a narrow, eastern branch of the "river." There are no surface connections between the two. A series of other sloughs through the Big Cypress Swamp supply freshwater to western Florida Bay and the Ten Thousand Islands.

Slough in the sawgrass Slough Detail White Fragrant Water Lilly

Tree Islands

Tree islands are the most distinct plant communities in the Everglades. In general, they consist of low trees, which occur on elevations slightly higher than the surrounding marsh areas. Depending on their origin, they can be circular or strand-like in shape within the landscape. Circular islands tend to be smaller and range from only about one-quarter acre to five or six acres in size. Tree island strands, which are teardrop shaped and oriented in a generally north to south direction, can grow much larger and sometimes exceed 300 acres in size. With the typical blunt end of the tear drop at the north end of strand tree islands, it is speculated that this orientation is the result of the southward movement of water from Lake Okeechobee to the southern rim of the Everglades, which until recently has been unimpeded. Depending on where the height is measured, tree islands can be a half-foot to four feet higher in elevation than the surrounding marsh. The northern blunt part of strand tree islands is also higher in elevation and tree density, which both gradually decrease as one moves south through the island. Species composition of islands is also dependent on location of a tree island within the landscape. Several types of tree islands have been described, such as bay heads, hammocks, willow, and cypress islands with each having their own unique species compositions.

hardwood Hammock in the Prarie

Landpatterns of EvergladesPatterns in the landscape of the historical Everglades suggest that the predrainage landscape was shaped into subtle ridges and sloughs, important to wildlife and movement of water southward. Analysis of these landscape features suggests two pathways for water flow through the ecosystem: the eastern flow path draining southeastward into the Atlantic Ocean and a western flow path draining southwestward through Shark Slough into the Gulf of Mexico. Evidence for these flow patterns also suggests a long, continuous downstream movement of water through the Everglades. Manmade structures have altered these flow pathways and may be causing the gradual loss of the ridge and slough pattern exhibited in the historic Everglades. Ongoing assessment of landscape patterns will be an important aspect of Everglades restoration.

Willow Heads - Coastal plain willow trees colonize rapidly from wind blown seeds, and may form discrete willow heads associated with a variety of disturbed habitats. The coastal plain willow prefers lower, wetter elevations than most species of the bay head community and is a good marker for an active alligator hole. Willow heads often mark the location of a bay head that has been completely destroyed by fire, especially where fire has burned the peat soil, reducing the elevation. Willow heads, in the long term, are typically displaced by other tree species.

Bay Heads - By far the most common type of tree island, bay heads often occur over discrete depressions of cavities in the limestone bedrock that are filled with peat soil to an elevation of one to 3 feet above the marsh. Bay heads are not uniformly distributed through the Everglades but are most common in the northeastern or Hillsborough lakes area , and the west central portion, throughout the Shark River Slough in the southern Everglades.

Cypress
The cypress tree (
Taxodium spp.) is a deciduous conifer, closely related to the redwood and sequoia trees of California. The seeds grow in muddy areas, but as they become trees, they can survive in standing water. This tree has "knees!" The knees are actually a part of the root system extending above the water near the base of the tree. Scientists are unsure of their use to the tree. Wherever cypress trees are found, you are likely to see bromeliads, orchids, and other air plants attached to their bark.

The cypress tree can be found in several areas of the Everglades. Both pond cypress and bald cypress grow here. In the open sawgrass, the trees appear to be dwarfed, but may, indeed, be older than much larger trees growing in different areas.

Dwarf pond cypress trees

Another area is the Cypress Dome. These sites are slightly lower in elevation and are almost circular in shape. The larger trees grow in the center creating a "dome." The soil is peat with acidic sand and limestone underneath.

Tree Island Everglades National Park

The largest concentration of cypress trees occurs in the cypress slough. Here, the soil is deeper and perhaps richer. The large cypress sloughs are found in the Big Cypress National Preserve. The water in the sloughs flows from the north to the southwest. During the summer wet season, the water may be three feet (0.9 m) deep. These deep cypress sloughs create giant trees that are well-adapted for life in the water. Each tree seems to have been individually decorated with ferns, orchids, and air plants. In some areas, small clumps of Spanish moss dangle from the trees above, creating what most people think is typical of the Everglades. Wood from these giants was prized for its durability. Most of the largest trees were harvested in the 1940's for pickle barrels and stadium seats. What remains today is second growth.

Big Cypress National Preserve on the northwest side of the Everglades is about one-third covered with cypress trees, mostly the dwarf pond cypress variety. Broad belts of these trees grow around the edge of wet prairies; cypress strands line the sloughs; and occasional cypress domes dot the horizon with the symmetry of paint bubbles. Giant cypresses are nearly gone. They are the great bald cypresses. Today’s few remaining giants, escapees of the lumber era, are extremely old; some as much as 600 to 700 years. Their bulbous bases flare downward and outward to root systems loosely locked in rich, wet organic peat. Their girths outstretch the combined embrace of you and 3 long-armed friends.

Hardwood Hammocks
Hammocks are dense stands of hardwood trees that grow on natural rises of only a few inches in the land. They appear as teardrop-shaped islands shaped by the flow of water in the middle of the slough. Many tropical species such as mahogany (
Swietenia mahogoni), gumbo limbo (Bursera simaruba), and cocoplum (Chrysobalanus icaco) grow here. Seeds of these plants originally drifted toward our shores in the currents of the Gulf Stream, or were carried here by hurricanes from the Caribbean. Alongside the tropical trees, the more familiar temperate species of live oak (Quercus virginiana), red maple (Acer rubum), and hackberry (Celtis laevigata). Because of their slight elevation, hammocks rarely flood. Acids from decaying plants dissolve the limestone around each tree island, creating a natural moat that protects the hammock plants from fire. Shaded from the sun by the tall trees, ferns and airplants thrive in the moisture-laden air inside the hammock.

Pinelands
The slash pine (
Pinus elliottii var. densa) is the dominant plant in this dry, rugged terrain that sits on top of a limestone ridge. The pines root in any crack or crevice where soil collects in the jagged bedrock. Fire is an essential condition for survival of the pine community, clearing out the faster-growing hardwoods that would block light to the pine seedlings. Pine bark is multi-layered, so only the outer bark is scorched during fires. The pinelands are the most diverse habitat in the Everglades, consisting of slash pine firest, an understory of saw palmettos (Serenoa repens), and over 200 varieties of tropical plants.

Florida Pinelands

The terrain of the pinelands is dry, rough, and rugged. The elevation is approximately six feet (1.8 m) above sea level. The limestone bedrock extends above ground, where years of erosion have shaped it into pinnacles. These pinnacles can make walking difficult. Throughout the jagged surface, there are solution holes containing small pockets of soil where the pines are rooted.

Pinnacles in Limestone Bedrock

The fern-like coontie plant (Zamia pumila) is one of the more famous residents of the pinelands. The Miccosukee Indians and early settlers collected them for their roots that were processed into starch for bread.

Kayak trip report in the Everglades..........

More about the Everglades..........

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