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Geography and ecology of the Everglades

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A tree island in a sawgrass prairie in the Everglades

The geography and ecology of the Everglades describes the complex elements that affect the natural environment throughout southern region of the U.S. state of Florida. The area recognized as the Everglades was originally a complex of marshes and prairies 4,000 square miles (10,000 km2) in area, spread over five counties. The Everglades is simultaneously a single geographic feature, a vast watershed that has historically extended from Lake Okeechobee 100 miles (160 km) south to Florida Bay, taking up approximately a third of the southern Florida peninsula, and many interconnecting ecosystems united within the geographic boundary. It is such a unique meeting of water, land, and climate that the use of both singular and plural to refer to the Everglades is correct.[1] When Marjory Stoneman Douglas wrote her definitive description of the region in 1947, she used the metaphor "River of Grass" to explain the joining of water and plant life in sawgrass marshes and freshwater sloughs.

Though sawgrass and sloughs are the enduring icons of the Everglades, along with alligators and the many species of wading birds, other ecosystems are just as vital, and borders marking them are subtle or do not exist at all. Tropical hardwood hammocks and pinelands are located throughout the sloughs and the trees support a variety of wildlife, rooted in soil inches above their surroundings. The oldest and tallest trees are cypresses, that are specially adapted to grow when their roots are underwater for months at a time. The Big Cypress Swamp is well-known for its 500-year-old trees, but cypress domes can appear throughout the Everglades. As the fresh water from Lake Okeechobee makes its way to Florida Bay, it meets salt water from the Gulf of Mexico. Mangrove forests grow in this transitional zone, providing nesting and nursery conditions for many species of birds, fish, and invertebrates. Even the marine environment of Florida Bay is considered part of the Everglades because its sea grasses and aquatic life are attracted to the constant discharge of fresh water.

These systems are constantly changing due to environmental factors. Geographic features such as the Western Flatwoods, Eastern Flatwoods, and the Atlantic Coastal Ridge affect drainage patterns. Geologic elements, climate, and the frequency of storms and fire help to create, maintain, or replace the ecosystems in the Shark River Valley, Big Cypress Swamp, coastal areas and mangrove forests. Author Michael Grunwald wrote of the first perceptions by observers, "If the Grand Canyon was a breathtaking painting, the Everglades was a complex drama, and everything in it had a role."[2]

Forming processes

Water

A storm over the Shark River in the Everglades, 1966

At only 5,000 years old, the Everglades is a young ecosystem geologically. Its ecosystems are in constant flux due to three factors: the type and amount of water present, the geology of the region, and the frequency and severity of fires. Water is the most dominant element in the Everglades, and it shapes the land, vegetation, and animal life in South Florida. Before its modern appearance, the South Florida climate was in turn arid and semi-arid, interspersed with periods of inundation. At the end of the Wisconsin ice age, sea levels rose, submerging portions of the Florida peninsula and causing the water table to rise. Fresh water saturated the limestone, eroding some of it, and created springs and sinkholes. The abundance of fresh water allowed new vegetation to take root, and formed convection thunderstorms over the land. As rain continued to fall, it provided more opportunities for solution: the tendency of the slightly acidic rainwater to dissolve limestone. As limestone wore away, the groundwater came into contact with the surface land, and created a massive wetland ecosystem.[3] Although the region appears flat, the wearing away of limestone in some areas creates slight valleys and plateaus (a matter of inches, usually) that not only affect the flow of water, but what types of vegetation take hold.

The Everglades are globally unique; no other wetland system is fed primarily from the atmosphere.[4] Before the first attempt at draining the Everglades in 1882, the entire watershed extended from Orlando to Florida Bay comprising the Kissimmee-Lake Okeechobee-Everglades (KLOE) watershed. The Kissimmee River outlets flow into Lake Okeechobee, which sits 18 feet (5.5 m) above sea level.[5] There are only two seasons in the Everglades: wet (May to November) and dry (December to April). Average annual rainfall in the Everglades is approximately 62 inches (160 cm), though episodic fluctuations of precipitation are normal.[6] Droughts, floods, and tropical storms are normal functions in the Everglades climate.[7] During the wet season when the lake exceeds its capacity, it pours slowly over the southern rim of the lake and flows for 100 miles (160 km) to Florida Bay. The gradient change is so slight that the river moves .5 miles (0.80 km) a day. Sawgrass thrives in this river, and the domination of sawgrass in freshwater marshes, or sloughs, is the main characteristic of what is commonly known as the Everglades.

The occurrence of severe weather in the form of tropical storms and hurricanes also affect the structure of the Everglades. Hurricanes are a natural occurrence; between 1871 and 2003, 40 tropical cyclones struck the Everglades, one every one to three years.[8][9] Severe storms alter the coastline, flush decaying vegetation buildup from estuaries, strip weakened branches from trees, disperse seeds, pollen, and plant material.[10] Hurricane Donna in 1960 altered 120 square miles (310 km2) of mangrove forests by depositing marl over the roots and depriving the trees of oxygen. It also eradicated orchids, bromeliads, and other epiphytes that once flourished in the mangroves; their reappearance may take a century or more. Donna also significantly spread buttonwood, saltwort, and glasswort, and epiphytes grew in areas they were previously unseen before the hurricane.[11] Although the lasting effects remain to be seen, Hurricane Andrew in 1992 also destroyed mangrove forests and snapped slash pines in half. However, regrowth occurred quickly, and scientists noted the added sand from the storm surge improved nesting conditions for crocodiles and sea turtles.[12]

Geology

Main article: Everglades § Geology

Though water is the dominant element of the Everglades, a vast marshland could not have been formed without the conditions of the underlying rock formations in southern Florida.[13] The floor of the Everglades formed between 2 million and 25 million years ago when the Florida peninsula was a shallow sea floor. The peninsula has been covered by sea water at least seven times since the earliest bedrock formation.[13] The rock that makes up the Everglades floor was created as layers of calcium carbonate were compressed by ocean water in many layers, making limestone. Fossilized bryozoans and tiny shells, or oolites, are in the limestone making it very porous. Water is stored in the rock, sometimes from one year to the next.[14] The length of time within a year that a region in the Everglades remains flooded is a hydroperiod,[15] and the length of a hydroperiod determines what soils are present and what kind of vegetation grows in that soil.

Shorter hydroperiods of three or four months promote beds of periphyton, a growth of algae and other microscopic organisms covered with calcium carbonate crystals.[13] Periphyton is the basic building block of marl, a calcitic mud. Where areas have longer hydroperiods of more than nine months, peat builds up over hundreds or thousands of years due to many generations of decaying plant matter. Peat and marl are considered nutrient-poor soils that foster the growth of specialized vegetation depending on the length of the regional hydroperiod.

There are five types of peat in the Everglades system, and each type supports a specific type of vegetation, from sawgrass to tree islands or custard apple trees.[16] Peat buildup is possible because water does not allow oxygen to decompose decaying plant matter quickly. Once peat buildup reaches the surface, oxygen reacts with the microorganisms to decay rapidly. Initial attempts at developing agriculture near Lake Okeechobee were successful, but the nutrients in the peat quickly deteriorated by drying, and encountered aerobic processes. The dried peat burned, or microorganisms degraded the peat into carbon dioxide and water. Some homes built in the areas of early farms had to have their foundations moved to stilts as the peat deteriorated; other areas lost approximately 8 feet (2.4 m) of soil depth.[17]

Fire

Fire near a cypress dome in the Turner River area in the early 1920s

Fire is an important element in the maintenance of the Everglades. The majority of fires are caused by lightning strikes from thunderstorms during the wet season. Their effects are largely superficial, and serve to foster further plant growth: sawgrass will burn above water, but the roots are preserved underneath. Fire in the sawgrass marshes serves to keep out larger bushes and trees, and releases nutrients from decaying plant matter more efficiently than decomposition.[18] Large areas of burned sawgrass affects waterflow as wind and water are not deterred by taller and thicker sawgrass, and water may flow two to three times faster in recently burned areas.[19] In the dry season, however, the effects of fire are much more significant. Whereas in the wet season, dead plant matter and the tips of grasses and trees are burned, in the dry season the fire may be fed by organic peat and burn deeply, destroying root systems. The only impediment to fire in the Everglades is the presence of water in the form of rain. It takes approximately 225 years for one foot (.30 m) of peat to develop, but there is less peat in the deepest portion of this organic material than should be for the 5,000 years of the Everglades' existence.[20] Scientists point to fire as the reason, as well as being the cause of the black muck appearance of the soils.

Researchers have noted a pattern in the occurrence of fire in the region that appears in cycles, associated with the cycles of hydroperiods.[20] The first cycle is the annual wet season fires during the summer that occur with rapid frequency, but are quickly extinguished. Dry season fires are rarer due to the lack of lightning, but their damage may be more pervasive.[18] A longer fire cycle spanning ten to fourteen years coincides with similar water cycles affected by global climate conditions. Fires in this cycle may be numerous and have little effect, or rare and have catastrophic consequences. The third cycle appears in a 550-year frequency associated with severe drought. Layers of charcoal have been detected in the peat in portions of the Everglades that indicate the region endured severe fires for years at a time, although this trend seems to have abated as the region formed into what it appears as today.[20]

Everglades

Major landscape types in the Everglades before human action. Source: U.S. Geological Survey

This area features the shallow river 100 miles (160 km) long and 60 miles (97 km) wide flowing from Lake Okeechobee to Florida Bay. Some authors refer to it as the "true Everglades" or just "the Glades".[21][22] Gifford Pinchot, an early environmentalist, said of the Everglades, "It is a region so different that it hardly seems to belong to the United States. It is full of the most vivid and most interesting life on land, in the air, and in the water. It is a land of strangeness, separate and apart from the common things we all know so well."[23] This is the titular "River of Grass" popularized by Marjory Stoneman Douglas in 1947. Prior to the first drainage attempts in 1905, the sheetflow, the wide shallow river starting in Lake Okeechobee, occupied nearly a third of the lower Florida peninsula.[24] The primary feature of this portion, and the defining characteristic of the Everglades, is sawgrass, although the ecosystems in the Everglades have several characteristics.

Sawgrass marsh

These marshes are dominated by the sedge known as Cladium, or sawgrass in common terminology. The sedge is a three-dimensional v-shaped stalk with upward pointing teeth. Sawgrass thrives in the slowly moving water, but may die under too much if oxygen is unable to reach its roots, and it is particularly vulnerable to floods immediately after a fire.[25] Some of the sawgrass can grow up to 6 feet (1.8 m) tall, but directly south of Lake Okeechobee, has grown to 10 feet (3.0 m). Farther south, where the peat is not as rich, it typically grows 4 feet (1.2 m) tall in various patches as opposed to the plain or prairie appearance of the upper glades.[26] The hydroperiod for the marsh is at least nine months, and can last longer. In shorter hydroperiods, marl may form instead of the peat.[27]

Where sawgrass grows densely, few animals or other plants thrive, although alligators choose these locations for nesting. Where there is more room, periphyton grows, appearing as brown sausage-shaped chunks. Periphyton is predominantly algae, although over 100 different microorganisms have a part in making it.[28] Larval insects and amphibians are supported by periphyton, and they feed birds, fish, and reptiles. It also absorbs calcium from water, which creates marl where sawgrass roots.[29]

Freshwater sloughs

Where sawgrass makes way for channels or free-flowing water, sloughs develop. The peat beds that support sawgrass is slightly elevated, and may begin abruptly creating ridges of grass. Sloughs are deeper than sawgrass marshes, about 3 feet (0.91 m), and may stay flooded for at least 11 months out of the year if not multiple years in a row.[30] The borders between these systems are called "ridge-and-slough" landscapes. Aquatic animals such as turtles, alligators, snakes, and fish live in sloughs; they usually feed on aquatic invertebrates, such as the Florida apple snail.[31] Plants grow here, but they may be submerged or floating like bladderwort, waterlily, or spatterdock. Major sloughs in the Everglades system include the Shark River Slough, Lostmans Slough bordering The Big Cypress, and Taylor Slough in the eastern Everglades.

Wet prairie

An alligator amid strands of periphyton in the Everglades

There are two kinds of wet prairies in the Everglades, marl and water-marsh community. Wet prairies are also slightly elevated like sawgrass marshes, but plant diversity is the primary characteristic. Marl prairies are located where calcitic soil, or marl, covers limestone that may protrude as pinnacles, or may be eroded into solution holes. The surface is covered only three to seven months of the year, and the water is usually shallow at only 4 inches (10 cm).[32] Marl is created by layers of periphyton loosely attached to the limestone. When it dries, it forms a grey or white crumbly mud. When flooded, the marl can support a variety of water plants, and dwarf cypresses may grow for hundreds of years though not reach more than 10 feet (3.0 m) tall.[33] Solution holes may remain flooded even when the prairies are dry, and they support aquatic invertebrates such as crayfish and snails, and larval amphibians which feed young wading birds.[34] Where the predominant soil is peat, a water-marsh community exists. Its hydroperiod is longer than the marl prairie, but its plants are less diverse. These regions tend to border between sloughs and sawgrass marshes.

Alligators have created a niche in wet prairies due to their activity. With their claws and snouts they dig at low spots and create ponds free of vegetation that remain submerged throughout the dry season. Alligator holes are integral to the survival of aquatic invertebrates, turtles, fish, small mammals, and birds during extended drought periods. Alligator hosts then feed upon some of what comes to the hole.[35][36]

Tropical hardwood hammock

In a tropical hardwood hammock, trees are very dense and diverse.

Islands of trees growing on land raised between 1 foot (0.30 m) and 3 feet (0.91 m) are called tropical hardwood hammocks.[37] They may appear in freshwater sloughs, sawgrass prairies, or pineland. Hammocks illustrate the difficulty of characterizing the climate of the Everglades as tropical or subtropical; the northern portion of the Everglades include more temperate plant species. Located closer to Florida Bay, the trees are tropical and smaller shrubs may be more prevalent. Tropical trees like the West Indian mahogany (Swietenia mahagoni) were probably spread by birds carrying seeds from the West Indies.[38]

The islets form on slightly elevated areas unharmed by deep peat fires, or limestone plateaus that rise several inches above the surrounding peat. Hardwood hammocks exhibit a mixture of subtropical and hardwood trees, such as Southern live oak (Quercus virginiana), gumbo limbo (Bursera simaruba), royal palm (Roystonea), and willow bustic (Dipholis salicifolia) that grow in very dense clumps.[39] Near the base sharp saw palmettos (Serenoa repens) flourish, making the hammocks very difficult to penetrate. Water in sloughs flow around the islands creating moats. Though some ecosystems are maintained and promoted by fire, hammocks may take decades or centuries to recover, so the moats around the hammocks protect the trees.[40] The islands vary in size but most range between one and ten acres; the water slowly flowing around them limits their size and gives them a teardrop appearance from above.[41] The height of the trees are limited to weather factors such as frost, lightning, and wind; the majority of trees in hammocks grow no higher than 55 feet (17 m).

Florida strangler figs (Ficus aurea) are common in hammocks, and find particular ease in rooting at the heads of cabbage palms (Sabal palmetto). After growing downward and taking root into the ground, they build complex frameworks around the host tree, eventually squeezing out light and nutrients, and essentially taking its place.[42] A variety of invertebrates including beetles, ants, spiders, and tree snails support a food chain that include frogs, owls and other birds of prey, snakes, rodents, bobcats, and raccoons. There are more than 50 varieties of tree snails in the Everglades; hammocks may be so isolated that tree snails have color patterns and designs unique to single islands.[43]

Tropical hardwood hammocks in the Everglades have been harvested for lumber, particularly by shipbuilders who found particular use for West Indian mahogany and black ironwood (Krugiodendron ferreum). The largest and most mature of these trees had been removed by the late 18th century.[44] Seminoles made their villages in hammocks in the late 19th and early 20th centuries; they lived in chickees numbering half a dozen with a central chickee for cooking and one for eating. Dugout canoes, cookware, stills, and sewing machines may still be seen in remote locations.[45]

Bayheads and willowheads

Some hammocks are dominated by certain types of vegetation that grows specifically due to the amount of water present, or the type of soil. The majority of hardwood hammocks create a thin poor soil covering the limestone called humus, made of decaying plant matter and moisture locked in by the structure of the trees. When the layer atop the limestone of a tree island is peat, bayheads develop, dominated by bay trees such as sweetbay (Laurus nobilis), and others like swamp holly (Ilex decidua), wax myrtle (Myrica cerifera) and cocoplum (Chrysobalanus icaco).[46] Willowheads, dominated by willow (Salix caroliniana) trees, take hold where the hydroperiod is long, usually around solution or alligator holes, and may surround the holes giving them a donut appearance from above.[47]

Flatwoods and the Atlantic Coastal Ridge

The Pine rockland ecosystem is dominated by South Florida slash pines and shrubs like saw palmettos.

The sawgrass prairies and freshwater sloughs of the Everglades system is bordered by two areas of poorly drained sandy soil on both sides of Lake Okeechobee: the Eastern Flatwoods, and the Western Flatwoods just north of Big Cypress swamp. These areas are dominated by pine forests, but cypress swamps and sloughs also occur in the Eastern Flatwoods.[48] Along the eastern border of the Everglades is the Atlantic Coastal Ridge, rising 20 feet (6.1 m) in elevation, and curving to the southwest, gradually decreasing in elevation until meeting with Taylor Slough. The Atlantic Coastal Ridge prevents Everglades water from flowing into the Atlantic Ocean to the east, causing it to flow southwesterly into Florida Bay. The South Florida metropolitan area is located on a portion of the Atlantic Coastal Ridge, and much of the landscape has changed drastically within the past 100 years as a result of urban growth.

Pine rockland

The most significant feature of the pine rockland ecosystem is the single species of South Florida slash pine (Pinus elliottii) (also called Dade County pine) that reaches a height of 22 feet (6.7 m). The pine forests are found on uneven limestone substrates that have pinnacles and solution holes. There are three primary locations for pine rocklands: the Miami Ridge, from Miami into Long Pine Key near the main entrance of Everglades National Park; the lower Florida Keys; and the Big Cypress Swamp.[49] Pine rockland communities require fire to maintain them, and have several adaptations that simultaneously promote and resist fire.[50] They are located in the highest part of the Everglades with little to no hydroperiod, although some floors may have flooded solution holes or puddles for a few months at a time. The sandy floor of the community is covered with dry pine needles that are highly flammable. South Florida slash pines are insulated by their bark to protect them from heat. Fire eliminates competing vegetation on the forest floor, and opens pine cones to germinate seeds.[51] A period without significant fire can turn pineland into hardwood hammock as larger trees overtake the slash pines.[52] The understory shrubs in pine rocklands are the fire-resistant saw palmetto, cabbage palm, and West Indian lilac. The most diverse group of plants in the pine community are the herbs, of which there are two dozen species. These plants contain tubers and other mechanisms that allow them to sprout quickly following being charred.[53]

Wildlife in pine rockland communities is diverse. In some forests, 15 species of birds can be found. Common among them are pine warbler, red-bellied woodpecker, and the eastern meadowlark. More than 20 species of reptiles and amphibians have been noted, such as the green anole, southern leopard frog, and black racer. Mammals such as the critically endangered Florida panther, Florida black bear, and several types of bats live in the pinelands.[50]

Pine rocklands covered approximately 161,660 acres in Miami-Dade County before development of the South Florida region. More than 12 miles (19 km) of north–south strands of pine rockland communities in the region have been lost. Pine forests were extensively cleared for urban development and the lumber industry in the 1930s and 1940s.[50] Dade County pine has a remarkable longevity and has proven to be termite-resistant, though dense enough to cause difficulty in driving nails into it.[54] Not until 1984 were they protected by a county ordinance. The misunderstanding of the role of fire also played a part in the disappearance of pine forests in the area, as natural fires were put out and pine rocklands transitioned into hardwood hammocks. Prescribed fires occur in Everglades National Park in pine rocklands every three to seven years.

The Big Cypress

To the west of the sawgrass prairies and sloughs lies the Big Cypress Swamp, commonly called "The Big Cypress." It takes up the majority of Collier County.[55] The Big Cypress is slightly elevated at 22 feet (6.7 m) at its highest point, and slopes gradually to the coastline for approximately 35 miles (56 km). The name refers to its size rather than the height or diameter of the trees; at its most limited measurement, the swamp measures 1,200 square miles (3,100 km2), but that more than doubles in considering its hydrologic boundary.[56] Because the defining feature of the Big Cypress is its trees, it is considered a swamp rather than a marsh, in which the main characteristic is grass.

Most of The Big Cypress sits atop a bedrock covered by a thinner layer of limestone. The limestone underneath the Big Cypress contains quartz, which creates sandy soil that hosts a different variety of vegetation.[57] The majority of trees are baldcypress (Taxodium distichum), and not true cypresses (Cupressaceae). The basin for The Big Cypress receives on average 55 inches (140 cm) of water in the rainy season.[58] Cypresses are conifers that are uniquely adapted to thrive in flooded conditions, with buttressed trunks and root projections that protrude out of the water, called "knees".[59]

Few massive trees survived the logging operations that took place in the 1930s and 1940s. As a result, much of The Big Cypress is protected by various federal or state agencies that include Big Cypress National Preserve, Corkscrew Swamp Sanctuary, Fakahatchee Strand State Preserve and two Indian reservations. Cypress trees in the area can live for hundreds of years; there are giants that grow to 130 feet (40 m) and are 500 years old. Still, they may be only seventh or eighth generation cypresses.[60]

Cypress head

A pond in The Big Cypress

Though The Big Cypress is the largest growth of cypress swamps in South Florida, they can be found near the Atlantic Coastal Ridge and between Lake Okeechobee and the Eastern flatwoods, as well as portions of sawgrass marshes. Hardwood hammocks and pineland are often interspersed with the cypress ecosystem. Much like tree islands, that are colloquially referred to as "heads", cypress trees grow in formations that resemble domes, with the tallest and thickest trunks in the center, rooted in the deepest peat. As the peat thins out, cypresses still grow, but are smaller and thinner, giving the small forest the appearance of a dome from the outside.[61] They also grow in strands, slightly elevated on a plateau of limestone and surrounded on two sides by sloughs.[62] Other hardwood trees can be found in cypress domes, such as red maple (Acer rubrum), swamp bay (Persea palustris), and pop ash (Fraxinus caroliniana). If cypresses are removed, the hardwoods take over, and the ecosystem is recategorized as a mixed swamp forest.

Because the cypress domes and strands keep in moisture and block out much of the sunlight, orchids, bromeliads, and ferns thrive in cypress domes and strands. Orchids bloom throughout the year in cypress heads, and bromeliads appear in many varieties; on Fakahatchee Strand alone, thirteen species have been documented.[63] Bromeliads collect moisture from rain and humidity in the bases of their leaves, that also serve as home to frogs, lizards and various insects. Wood storks nest almost exclusively in cypress forests, and in the past 100 years have seen a dramatic decline, probably due to lack of reproduction tied to controlled water. Wood storks' reproductive cycles coincide with the dry season, when small fish and amphibians are trapped in shallow pools and puddles. When water from canals or locks is released too soon or not at all, the storks are unable to find enough food to feed themselves and their offspring. An estimated 20,000 wood storks nested in The Big Cypress in the 1930s, but by the 1990s less than ten percent of that number were counted.[64]

Mangrove and Coastal prairie

Red mangrove trees bordering a tidal estuary in the Everglades

Water from Lake Okeechobee and The Big Cypress eventually makes its way out to the ocean. Where fresh water meets salt water is a transitional zone where mangrove trees live, and are specially adapted to both kinds of water. This mixture is known as brackish water, and the mangrove systems, crisscrossed by hundreds of tidal creeks, harbor a very productive ecosystem. The depth of these zones is dependent on how much water flows from the Everglades. In the wet season the fresh water pours out into Florida Bay and sawgrass appears closer to the coastline. In dryer years, the salt water creeps inland into the coastal prairie, an ecosystem that buffers the freshwater marshes by absorbing sea water. Mangrove trees grow in fresh water ecosystems when the salt water goes far enough inland.[65] The Everglades have the most extensive continguous system of mangroves in the world.[66] The estuarine ecosystem of the Ten Thousand Islands covers almost 200,000 acres (81,000 ha).[67]

Mangrove

There are three species of trees that are considered mangrove: red (Rhizophora mangle), black (Avicennia germinans), and white (Laguncularia racemosa), although all are from different families.[68] All have the same characteristics: they are tolerant of salt, brackish, and fresh water, grow in oxygen-poor soil, and can survive drastic water level changes.[69] Black and white mangroves excrete salt from under their leaves, and red mangroves filter the salinity in sea water. All species are integral to coastline protection during severe storms. Red mangroves have roots that reach far, trapping sediments in between. All three trees absorb the energy of waves and storm surges.

The estuaries act as fisheries for fry, and a nursery for crustaceans: more than 90 percent of species that are harvested commercially are born or spend time in the shallow waters near the Everglades.[70] Shrimp, oysters, crabs, whelks, cockles, and snails thrive in these waters, as do ancient horseshoe crabs. Oysters and mangroves work in tandem to build up the coastline. The sand around the coastline is white and has minute particles of quartz and fine shells. When currents are right, oysters grow in colonies or beds, and deposit their shells, building up the bed. Mangrove seeds, called propagules, are full embryos and float in water until they reach somewhere favorable and take root, often on oyster beds. They shed skin and litter, ensuring other trees will not compete for space and nutrients.[71]

Mangroves serve as excellent rookeries for birds. Wading birds, such as roseate spoonbills, egrets, and tri-colored herons use the mangroves as a nursery, due to the proximity of food sources and the protection offered from most prey. Thousands of birds can nest in the mangroves at once, making a noisy and messy colony, but their droppings further the mangrove trees.[72] Shorebirds like rails, terns and gulls, diving birds such as pelicans and grebes, and birds of prey such as ospreys, hawks and vultures are some of the more than one hundred species of birds that use mangrove trees to protect and raise their chicks.

Florida Bay

A clump of mangroves in the distance, Florida Bay at Flamingo

Because much of the coast and the inner estuaries are built by mangroves, and there is no border between the coastal marshes and the bay, the ecosystems in Florida Bay are considered to be a part of the Everglades. More than 800 square miles (2,100 km2) of Florida Bay is protected by Everglades National Park, representing the largest body of water in the park boundaries.[73] There are approximately a hundred keys in Florida Bay, many of which are mangrove forests.[74] Those that grow larger may be taken over by hardwood hammocks. The outer rims of the Ten Thousand Islands and Cape Sable share characteristics of the intertwining saltwater bays and fresh water marshes.

The fresh water coming into Florida Bay from the Everglades creates perfect conditions for vast beds of turtle grass and algae formations that are the foundation for the animal life in the bay. Sea turtles and manatees eat the grass, while invertebrate animals, such as worms, clams and other mollusks eat the algae formations and microscopic plankton.[75] The Calusa Indians found the shell of the horse conch particularly useful in making tools.[76] Female sea turtles return annually to nest on the shore, and manatees spend the winter months in the warmer water of the bay.

Sea grasses also serve to stabilize the sea beds and protect shorelines from erosion by absorbing energy from waves. Shrimp, spiny lobsters, and sea urchins also live in and among the grasses and feed on the phytoplankton, and they in turn feed larger predators such as sharks, rays, barracuda, and king mackerel.[77] Due to the shallow waters and the amount of sunlight, Florida Bay hosts communities of coral reefs and sponges although the majority of Florida's reefs are closer to the Keys.[78] The keys that foster mangroves support wading bird nurseries for birds such as the Great white heron that was almost wiped out in the Labor Day Hurricane of 1935 when only 146 were counted afterward.[79] After recovering to number more than two thousand, they were further endangered by the effects of Hurricane Donna in 1960, which decreased their numbers by 35 to 40 percent.[80]

The sea floor patterns of Florida Bay are formed by currents and winds. However, since 1932, sea levels have been recorded rising at a rate of 1 foot (0.30 m) per 100 years. If the trend continues, within 500 years there may be a complete loss of land in the Keys.[81] Similarly, though mangroves serve to build and stabilize the coastline, seas may be rising more rapidly than the trees are able to build coastal areas.[82]

Biodiversity

Ecosystems in the Everglades have been described as both fragile and resilient.[83] There are 11,000 species of seed-bearing plants and 400 species of land or water vertebrates that live in the Everglades, but slight variations in water levels affect many organisms and reshape land formations. The health and productivity of any ecosystem relies on the number of species present; the loss of one species weakens the entire ecosystem.[84]

For example, the Florida apple snail (Pomocea palludosus) is an amphibious fresh water mollusk.[85] They have a single gill and lung, and live on the stalks of sawgrass in water depths no more than 20 inches (51 cm). They are also the primary food of the endangered Everglades snail kite, the limpkin, and raccoons, otters, and young alligators. Apple snails lay their eggs on sawgrass stalks about 6 inches (15 cm) above the water line, and they are intolerant of being submerged for long periods of time. When the eggs hatch, the young snails must enter the water quickly or they will die. When water levels are too low or they rise too quickly when snail eggs are developing, and apple snails do not flourish, it affects the many reptiles, mammals, and birds that feed on them.[86] In terms of the ecology of trophic dynamics, or food chains, the 174  species of invertebrates play a vital role in the Everglades.[87] Crayfish, insects, scorpions, and other invertebrates also support a web of animals.

The group of animals most integral to the overall success of Everglades wildlife is freshwater fish. Few places in the Everglades stay submerged from one year to the next, so alligator holes and rocky crags are vital to their survival. Freshwater fish are the main diet of most wading birds, alligators, and otters, and require large areas of open water in order to repopulate areas within a season. Young amphibians also play an important role in the food chain. Tadpoles and pollywogs spread quickly in isolated areas where fish do not have the time or access to reproduce in numbers necessary to support larger animals. There are hundreds of species of amphibians in the Everglades, and their availability helps support wildlife during short hydroperiods or in remote locations.[88]

These smaller animals support smaller communities of larger animals, including 70 species of land birds that breed within the Everglades, and 120 water birds, of which 43 breed in the area. Many of these birds migrate through the West Indies and North America, and use the Everglades as a breeding ground.[89] There are several dozen species of mammals that span from the smallest bats or shrews to midsize raccoons, otters, opossums, and foxes, to the largest: white tailed deer, Florida black bear, and the Florida panther.[90]

Although slight changes in water level affect many species, it is also true that the system as a whole cycles and pulses with each change. Some transformations to the diversity of plant and animal life are natural, such as fire and storms, and some are induced by humans, such as urban encroachment and the introduction of exotic species. Some species, such as snail kites and apple snails do well in wet conditions, but wood storks and Cape Sable Seaside Sparrows do well in dryer conditions. Conditions of the Everglades favor no particular species.[83]

See also

Notes

  1. ^ Lodge, p. 13.
  2. ^ Grunwald, p. 14.
  3. ^ McCally, p. 9–10.
  4. ^ Lodge, p.14.
  5. ^ Lodge, p. 18–19.
  6. ^ U.S. Geological Survey (2004). "Environmental Setting - The Natural System: Climate". Circular 1134: The South Florida Environment - A Region Under Stress. U.S. Department of the Interior. Retrieved 2008-03-17.
  7. ^ Obeysekera, Jayantha (October, 1999). "The natural South Florida system I: Climate, geology, and hydrology". Urban Ecosystems. 3. Kluwer Academic Publishers: 223–244. {{cite journal}}: Check date values in: |date= (help); Cite has empty unknown parameter: |1= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  8. ^ Hurricane Research Division (2008). "Atlantic hurricane best track". NOAA. Retrieved 2008-05-03.
  9. ^ Lodge, p. 89.
  10. ^ Jewell, p. 35.
  11. ^ Lodge, p. 89–93.
  12. ^ Toops, p. 95.
  13. ^ a b c Gleason, Patrick, Peter Stone, "Age, Origins, and Landscape Evolution of the Everglades Peatland" in Everglades: The Ecosystem and its Restoration, Steven Davis and John Ogden, eds. (1994), St. Lucie Press. ISBN 0963403028
  14. ^ McCally, p. 12–14.
  15. ^ McCally, p. 9–10.
  16. ^ McCally, p. 15–17
  17. ^ Lodge, p. 38.
  18. ^ a b Lodge, p. 39–41.
  19. ^ Schaffraneck, Raymond (September 3, 2003). "Fire Effects on Flow in Vegetated Wetlands of the Everglades". U.S. Geological Survey. Retrieved 2008-05-02. {{cite web}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  20. ^ a b c McCally, p. 18–21.
  21. ^ George, p. 13.
  22. ^ Douglas, p. 11.
  23. ^ Grunwald, p. 12.
  24. ^ McCally, p. 9–10.
  25. ^ Whitney, p. 168.
  26. ^ Lodge, p. 25–27.
  27. ^ Jewell, p. 46.
  28. ^ Whitney, p.168.
  29. ^ George, p. 42.
  30. ^ Lodge, p. 31.
  31. ^ George, p. 14.
  32. ^ Lodge, p. 29.
  33. ^ Whitney, p. 164.
  34. ^ Whitney, p. 163.
  35. ^ George, p. 45–46.
  36. ^ Lodge, p. 35.
  37. ^ George, p. 30.
  38. ^ Lodge, p. 55.
  39. ^ Douglas, p. 48–49.
  40. ^ George, p. 31.
  41. ^ Toops, p. 53.
  42. ^ Lodge, p. 58.
  43. ^ Toops, p. 57.
  44. ^ Lodge, p. 55.
  45. ^ Toops, p. 61.
  46. ^ George, p. 39.
  47. ^ Lodge, p. 45–46.
  48. ^ McCally, p. 9.
  49. ^ Jewell, p. 45.
  50. ^ a b c U.S. Fish & Wildlife Service. "South Florida Multi-Species Recovery Plan: Pine rockland", Retrieved May 3, 2008.
  51. ^ George, p. 7–8.
  52. ^ "Land and Resource Management Projects". DOI science plan in support of ecosystem restoration, preservation, and protection in South Florida. U.S. Geological Survey. April 26, 2007. Retrieved 2008-05-02. {{cite web}}: Check date values in: |date= (help)
  53. ^ Lodge, p. 66.
  54. ^ Lodge, p. 63.
  55. ^ George, p. 26.
  56. ^ Lodge, p. 67.
  57. ^ George, p. 26.
  58. ^ Ripple, p. 16.
  59. ^ Jewell, p. 43.
  60. ^ Ripple, p. 19–20.
  61. ^ Ripple, p. 26.
  62. ^ Ripple, p. 31–32.
  63. ^ Ripple, p. 28.
  64. ^ Ripple, p. 30–38.
  65. ^ George, p. 19.
  66. ^ Katherisen, K. (2001). "Biology of Mangroves and Mangrove Ecosystems", Advances in Marine Biology, Alan J. Southward (ed.) 40, p. 18–251. ISBN 9780120261406.
  67. ^ Ripple, p. 80.
  68. ^ Jewell, p. 41.
  69. ^ Whitney, p. 286.
  70. ^ Ripple, p. 80.
  71. ^ Whitney, p. 288–289.
  72. ^ Whitney, p. 295–296.
  73. ^ "Ecosystems: Marine & Estuarine". National Park Service. July 30, 2007. Retrieved 2008-05-04.
  74. ^ George, p. 21.
  75. ^ Whitney, p. 313–316.
  76. ^ Jewell, p. 51–52.
  77. ^ Whitney, p. 328–330.
  78. ^ Jewell, p. 40.
  79. ^ Toops, p. 88.
  80. ^ Williams, p. 26.
  81. ^ Lodge, p. 100.
  82. ^ Lodge, p. 104.
  83. ^ a b Toops, p. 92.
  84. ^ Whitney, p. 383.
  85. ^ Whitney, p. 241.
  86. ^ Lodge, p. 136.
  87. ^ Lodge, p. 140.
  88. ^ Lodge, p. 160.
  89. ^ Lodge, p. 183–185.
  90. ^ Lodge, p. 175–180.

Bibliography

  • Douglas, Marjory (1947). The Everglades: River of Grass. R. Bemis Publishing, Ltd. ISBN 0912451440
  • George, Jean (1972). Everglades Wildguide. National Park Service. Gov. doc #I 29.62:Ev2
  • Grunwald, Michael (2006). The Swamp: The Everglades, Florida, and the Politics of Paradise, Simon & Schuster. ISBN 0743251075
  • Jewell, Susan (1993). Exploring Wild South Florida: A Guide to Finding the Natural Areas and Wildlife of the Everglades and Florida Keys, Pineapple Press, Inc. ISBN 1561640239
  • Lodge, Thomas E. (1994). The Everglades Handbook: Understanding the Ecosystem. CRC Press. ISBN 1884015069
  • McCally, David (1999). The Everglades: An Environmental History. University Press of Florida. ISBN 0813023025
  • Ripple, Jeff (1992). Big Cypress Swamp and the Ten Thousand Islands: Eastern America's Last Great Wilderness, University of South Carolina Press. ISBN 0872498425
  • Toops, Connie (1998). The Florida Everglades. Voyageur Press. ISBN 0896583724
  • Whitney, Ellie et al., eds. (2004) Priceless Florida: Natural Ecosystems and Native Species. Pineapple Press, Inc. ISBN 9781561643097
  • Williams, John (2002). Florida hurricanes and tropical storms, 1871-2001. University of Florida Press. ISBN 0813024943
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