The Everglades is both a vast watershed in southern Florida and many interconnected tropical wetlands ecosystems within a geographic boundary. Formed about 5,000 years ago, it has historically covered around one-third of the southern Florida peninsula, from Lake Okeechobee 100 miles (160 km) south to Florida Bay. Before drainage, its interwoven mesh of marshes and prairies covered 4,000 square miles (10,000 km2). It is such a unique meeting of water, land, and climate that the use of either singular or plural to refer to the Everglades is appropriate. When Marjory Stoneman Douglas wrote her definitive description of the region in 1947, she used the metaphor "River of Grass" to explain the blending of water and plant life. Although sawgrass and sloughs are the enduring geographical icons of the Everglades, other ecosystems are just as vital, and the borders marking them are subtle or nonexistent. Pinelands and tropical hardwood hammocks are located throughout the sloughs; the trees, rooted in soil inches above the peat, marl, or water, support a variety of wildlife. The oldest and tallest trees are cypresses, whose roots are specially adapted to grow underwater for months at a time. The Big Cypress Swamp is well known for its 500-year-old cypresses, though cypress domes can appear throughout the Everglades. As the freshwater from Lake Okeechobee makes its way to Florida Bay, it meets saltwater from the Gulf of Mexico; mangrove forests grow in this transitional zone, providing nursery and nesting conditions for many species of birds, fish, and invertebrates. The marine environment of Florida Bay is also considered part of the Everglades because its seagrasses and aquatic life are attracted to the constant discharge of freshwater. These ecological systems are always changing due to environmental factors. Geographic features such as the Western Flatwoods, Eastern Flatwoods, and Atlantic Coastal Ridge affect drainage patterns. Geologic elements, climate, and the frequency of storms and fire are formative processes for the Everglades. They help to sustain and transform the ecosystems in the Shark River Valley, Big Cypress Swamp, coastal areas, and mangrove forests. Ecosystems have been described as both fragile and resilient. Minor fluctuations in water levels have far-reaching consequences for many plant and animal species, and the system cycles and pulses with each change.
Shaping processes of ecosystems At only 5,000 years of age, the Everglades is a young region in geological terms. Its ecosystems are in constant flux as a result of the interplay of three factors: the type and amount of water present, the geology of the region, and the frequency and severity of fires.
Water
Water is the dominant element in the Everglades, and it shapes the land, vegetation, and animal life of South Florida. The South Florida climate was once arid and semi-arid, interspersed with wet periods. Between 10,000 and 20,000 years ago, 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 creating springs and sinkholes. The abundance of fresh water allowed new vegetation to take root, and through evaporation formed thunderstorms. Limestone was dissolved by the slightly acidic rainwater. The limestone wore away, and groundwater came into contact with the surface, creating a massive wetland ecosystem. Although the region appears flat, the wearing away of the limestone in some areas created slight valleys and plateaus—a difference of inches in elevation—that affected the flow of water and types of vegetation present. The Everglades are unique; no other wetland system in the world is nourished primarily from the atmosphere. 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 flows into Lake Okeechobee, which sits 18 feet (5.5 m) above sea level. Only two seasons exist 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 fluctuations of precipitation are normal. Droughts, floods, and tropical storms are normal occurrences in the area. When Lake Okeechobee exceeds its water storage capacity during the wet season, it pours slowly over the southern rim and flows for 100 miles (160 km) to Florida Bay. The gradient change is so slight that the river moves only 2 feet (0.61 m) a minute. Sawgrass thrives in this river, dominates freshwater marshes and sloughs, and is the main characteristic of the region. Severe weather, in the form of tropical storms and hurricanes, also affects the structure of the Everglades. Between 1871 and 2003, 40 tropical cyclones struck the Everglades, usually every one to three years. These storms alter the coastline, flush decaying vegetation from estuaries, strip weakened branches from trees, and disperse seeds, pollen, and plant material. Hurricane Donna in 1960 affected 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 began to grow in new areas. 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 sand deposited by the storm surge improved nesting conditions for crocodiles and sea turtles.
Geology
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