Ecosystems
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Main article: Geography and ecology of the Everglades
The Everglades landscape is noted for its biodiversity. At the turn of the 20th century, common concepts of what should be protected in national parks invariably included formidable geologic features like mountains, geysers, or canyons. As Florida's population began to grow significantly and urban areas near the Everglades were developed, proponents of the park's establishment faced difficulty in persuading the federal government and the people of Florida that the subtle and constantly shifting ecosystems in the Everglades were just as worthy of protection. When the park was established in 1947, it became the first area within the U.S. to protect flora and fauna native to a region as opposed to geologic scenery. The National Park Service recognizes nine distinct interdependent ecosystems within the park that constantly shift in size owing to the amount of water present and other environmental factors.
Freshwater sloughs and marl prairies[edit]
Alligators thrive in freshwater sloughs and marl prairies.
Alligator in freshwater swamp
Freshwater sloughs are perhaps the most common ecosystem associated with Everglades National Park. These drainage channels are characterized by low-lying areas covered in fresh water, flowing at an almost imperceptible 100 feet (30 m) per day. These slow-moving channel-like rivers are not just features in the landscape but are central to a flow formed landscape that includes parallel ridges of higher ground. The historical broad sheet flow from Lake Okeechobee provided the consistent energy to build this ridge and slough pattern, scouring the sloughs deeper and building the peat ridges with transported sediment and organic matter. Shark River Slough and Taylor Slough are significant features of the park. Sawgrass growing to a height of 6 feet (1.8 m) or more, and broad-leafed marsh plants, are so prominent in this region that they gave the Everglades its nickname "River of Grass", cemented in the public imagination in the title for Marjory Stoneman Douglas's book (1947), which culminated years of her advocacy for considering the Everglades ecosystem as more than a "swamp". Excellent feeding locations for birds, sloughs in the Everglades attract a great variety of waders such as herons, egrets, roseate spoonbills (Platalea ajaja), ibises and brown pelicans (Pelecanus occidentalis), as well as limpkins (Aramus guarauna) and snail kites that eat apple snails, which in turn feed on the sawgrass. The sloughs' availability of fish, amphibians, and young birds attract a variety of freshwater turtles, American alligator (Alligator mississippiensis), Florida cottonmouth (Agkistrodon conanti)), and eastern diamondback rattlesnake (Crotalus adamanteus).
A great blue heron along the Anhinga Trail
Freshwater marl prairies are similar to sloughs but lack the slow movement of surface water; instead, water seeps through a calcitic mud called marl. Algae and other microscopic organisms form periphyton, which attaches to limestone. When it dries it turns into a gray mud. Sawgrass and other water plants grow shorter in freshwater marl than they do in peat, the other type of soil in the Everglades which is found where water remains present longer throughout the year. Marl prairies are usually under water from three to seven months of the year, whereas sloughs may remain submerged for longer than nine months and sometimes remain under water from one year to the next. Sawgrass may dominate sloughs, creating a monoculture. Other grasses, such as muhly grass (Muhlenbergia sericea) and broad-leafed water plants can be found in marl prairies. Animals living in the freshwater sloughs also inhabit marl prairies. Marl prairies may go dry in some parts of the year; alligators play a vital role in maintaining life in remote parts of the Everglades by burrowing in the mud during the dry season, creating pools of water where fish and amphibians survive from one year to the next. Alligator holes also attract other animals who congregate to feed on smaller prey. When the region floods again during the wet season, the fish and amphibians which were sustained in the alligator holes then repopulate freshwater marl prairies.
Tropical hardwood hammocks[edit]
Main article: Tropical hardwood hammock
Hammocks are often the only dry land within the park. They rise several inches above the grass-covered river and are dominated by diverse plant life consisting of subtropical and tropical trees, such as large southern live oaks (Quercus virginiana). Trees often form canopies under which animals thrive amongst scrub bushes of wild coffee (Psychotria), white indigoberry (Randia aculeata), poisonwood (Metopium toxiferum) and saw palmetto (Serenoa repens). The park features thousands of these tree islands amid sloughs—which often form the shape of a teardrop when seen from above (see park map) because of the slowly moving water around them—but they can also be found in pineland and mangroves. Trees in the Everglades, including wild tamarind (Lysiloma latisiliquum) and gumbo-limbo (Bursera simaruba), rarely grow higher than 50 feet (15 m) because of wind, fire, and climate.
About 160 Florida panthers inhabit hammocks and pinelands of the Everglades.
The plant growth around the hammock base is nearly impenetrable; beneath the canopy hammocks is an ideal habitat for animals. Reptiles (such as various species of snake and anole) and amphibians (such as the American green tree frog, Hyla cinerea), live in the hardwood hammocks. Birds such as barred owls (Strix varia), woodpeckers, northern cardinals (Cardinalis cardinalis), and southern bald eagles (Haliaeetus leucocephalus leucocephalus) nest in hammock trees. Mammal species living in hardwood hammocks include Florida black bears (Ursus americanus floridanus), red foxes (Vulpes vulpes), minks (Neogale vison), marsh rabbits (Sylvilagus palustris), gray foxes (Urocyon cinereoargenteus), white-tailed deer (Odocoileus virginianus), and the rare, critically endangered Florida panther (Puma concolor couguar).
Pineland[edit]
Sunrise on the pine rocklands on Long Pine Key Nature Trail
Miami-Dade County was once covered in 186,000 acres (290.6 sq mi; 752.7 km2) of pine rockland forests, but most of it was harvested by the lumber industry. Pineland ecosystems (or pine rocklands) are characterized by shallow, dry sandy loam over a limestone substrate covered almost exclusively by slash pines (Pinus elliottii var. densa). Trees in this ecosystem grow in solution holes, where the soft limestone has worn away and filled with soil, allowing plants to take hold. Pinelands require regular maintenance by fire to ensure their existence. South Florida slash pines are uniquely adapted to promote fire by dropping a large amount of dried pine needles and shedding dry bark. Pine cones require heat from fires to open, allowing seeds to disperse and take hold. The trunks and roots of slash pines are resistant to fire. Prescribed burns in these areas take place every three to seven years; without regular fires, hardwood trees begin to grow in this region, and pinelands become recategorized as mixed swamp forests. Most plants in the area bloom about 16 weeks after a fire. Nearly all pinelands have an understory of palm shrubs and a diverse ground covering of wild herbs.
Pine rocklands are considered one of the most threatened habitats in Florida; less than 4,000 acres (6.3 sq mi; 16.2 km2) of pineland exist outside the park. Within the park, 20,000 acres (31.3 sq mi; 80.9 km2) of pineland are protected. A variety of animal species meet their needs for food, shelter, nesting, and rooking in pine rocklands. Woodpeckers, eastern meadowlarks (Sturnella magna), loggerhead shrikes (Lanius ludovicianus), grackles, and northern mockingbirds (Mimus polyglottos) are commonly found in pinelands. Black bears and Florida panthers also live in this habitat.
Cypress and mangrove[edit]
Alligator in a cypress dome
Cypress trees are conifers that are adapted to live in standing fresh water. They grow in compact structures called cypress domes and in long strands over limestone. Water levels may fluctuate dramatically around cypress domes and strands, so cypresses develop "knees" that protrude from the water at high levels to provide oxygen for the root systems. Dwarf cypress trees grow in drier areas with poorer soil. Epiphytes, such as bromeliads, Spanish moss (Tillandsia usneoides), orchids and ferns grow on the branches and trunks of cypress trees. Everglades National Park features twenty-five species of orchids. Tall cypress trees provide excellent nesting areas for birds including wild turkey (Meleagris gallopavo), ibis, herons, egrets, anhingas (Anhinga anhinga), and belted kingfisher (Megaceryle alcyon). Mammals in cypress regions include white-tailed deer, squirrels, raccoons, opossums, skunks, swamp rabbits, river otters (Lontra canadensis), and bobcats, as well as small rodents.
Mangrove trees cover the coastlines of South Florida, sometimes growing inland depending on the amount of salt water present within the Everglades ecosystems. During drier years when less fresh water flows to the coast, mangroves will appear among fresh water plants. When rain is abundant, sawgrass and other fresh water plants may be found closer to the coast. Three species of mangrove trees—red (Rhizophora mangle), black (Avicennia germinans), and white (Laguncularia racemosa)—can be found in the Everglades. With a high tolerance of salt water, winds, extreme tides, high temperatures, and muddy soils, mangrove trees are uniquely adapted to extreme conditions. They act as nurseries for many marine and bird species. They are also Florida's first defense against the destructive forces of hurricanes, absorbing flood waters and preventing coastal erosion. The mangrove system in Everglades National Park is the largest continuous system of mangroves in the world.
Manatees inhabit shallow water around mangroves.
Within the Florida mangrove systems live 220 species of fish, and a variety of crabs, crayfish, shrimp, mollusks, and other invertebrates, which serve as the main source of food for many birds. Dozens of bird species use mangroves as nurseries and food stores, including pelicans, grebes, tricolored herons (Egretta tricolor), gulls, terns, hawks and kites, and arboreal birds like mangrove cuckoos (Coccyzus minor), yellow warblers (Dendroica petechia), and white-crowned pigeons (Patagioenas leucocephala). The mangroves also support 24 species of amphibians and reptiles, and 18 species of mammals, including the endangered green turtle (Chelonia mydas), hawksbill sea turtle (Eretmochelys imbricata), and West Indian manatee (Trichechus manatus).
Coastal lowlands[edit]
Coastal lowlands, or wet prairies, are salt water marshes that absorb marine water when it gets high or fresh water when rains are heavy. Floods occur during hurricane and tropical storm surges when ocean water can rise several feet over the land. Heavy wet seasons also cause floods when rain from the north flows into the Everglades. Few trees can survive in the conditions of this region, but plants—succulents like saltwort and glasswort—tolerate salt, brackish water, and desert conditions. Animal life in this zone is dependent upon the amount of water present, but commonly found animals include Cape Sable seaside sparrow (Ammodramus maritimus mirabilis), Everglades snail kite (Rostrhamus sociabilis), wood stork (Mycteria americana), eastern indigo snake (Drymarchon couperi), and small mammals such as rats, mice, and rabbits.
Marine and estuarine[edit]
Mangroves reduce coastal erosion and shelter wildlife.
The largest body of water within the park is Florida Bay, which extends from the mangrove swamps of the mainland's southern tip to the Florida Keys. Over 800 square miles (2,100 km2) of marine ecosystem lies in this range. Coral, sponges, and seagrasses serve as shelter and food for crustaceans and mollusks, which in turn are the primary food source for larger marine animals. Sharks, stingrays, and barracudas also live in this ecosystem. Pelicans, shorebirds, terns, and black skimmers (Rynchops niger) are among the birds frequenting park shorelines. The bay also has its own resident population of bottlenose dolphin (Tursiops truncatus). Seagrass meadows in Florida Bay and estuaries that are close by, are very important in the environment. They are there to stabilize sediments, support fisheries, and act as some sort of a buffer for coastal habitats against disturbance. Recent research shows us that these seagrass communities can be quite resilient but are vulnerable whenever there are rule changes that make them exposed to a variety of different stressors. These stressors can be things like warming waters along with altered salinity and the constant declining water quality. The study mentions that freshwater inflows from the Everglades is a strong influence on patterns of salinity, which means that changes in upstream water management can be the determining factor as to whether seagrass meadows persist or collapse .
The bay's many basins are broken up by sandbanks that serve as plentiful recreational fishing grounds for snook (Centropomus undecimalis), redfish (Sciaenops ocellatus), spotted seatrout (Cynoscion nebulosus), tarpon (Megaflops atlanticus), bonefish (Albula vulpes), and permit (Trichinous falcatus), as well as snapper (Lutjanus campechanus), bluegill (Lepomis macrochirus), and bass. Wading birds such as roseate spoonbills (Platalea ajaja), reddish egrets (Egretta rufescens), and great white herons (Ardea herodias occidentalis) have unique subpopulations that are largely restricted to Florida Bay. Other bird species include bald eagles, cormorants, and ospreys. Mammals along the shoreline include raccoons, opossums, bobcats, and fox squirrels.
