The Everglades ecoregion, situated at the southern tip of peninsular Florida, is the most noted wetland in the USA and one of the most distinct in the world. The Everglades is unique among the world's large wetlands because it derives most of its water input from rainfall. Other large notable wetlands, such as the Pantanal of South America, the Okavango alluvial fan of Botswana, and the Llanos in Venezuela and Colombia, derive most of their water and nutrient inputs from river flooding. The unique sheet flow, the languid flow of surface water over shallow, broad tracts of marsh, inspired Douglas to name the Everglades, River of Grass. As important as sheet flow is, the groundwater connections of the Everglades to Lake Okeechobee, the second largest freshwater lake entirely within the USA, are also essential for the maintenance of the wetland. The linkages between the Everglades, Lake Okeechobee, and the Kissimmee River, which provides 80 percent of the surface flow into Lake Okeechobee, illustrate the importance of connectivity among ecoregions to maintain habitat integrity.
The boundaries of this ecoregion extend to include the Big Cypress Swamp to the northwest, the southern edge of Lake Okeechobee to the north, and the Atlantic coastal ridge to the east. The Everglades climate is classified as subtropical, featuring hot humid summers, when eighty marshes and Lake Okeechobee only receive about 60 percent of the rainfall levels recorded in the coastal areas. The most important climatic feature is also the most important natural disturbance factor: the recurrent hurricanes that strike most frequently from August through October. Extensive habitat destruction can occur from high winds, storm surge, and rainfall. Frosts also limit the northern distribution of many tropical species to this ecoregion and help to further define its boundaries.
Many researchers have identified the Everglades as one of the most endangered of North American ecoregions as a result of clearing for agriculture, diversion of water flow, and other human modifications. Recovery efforts are presently underway, supported by a broad association of environmental organizations active in the region.
The extraordinary biological richness of the Everglades has been well-documented, particularly the spectacular wading birds, alligators, crocodiles, snail kites, and mangrove species. The habitats that support this rich assemblage of species include: ponds, sloughs, graminoid (grass-like wetlands), and forested wetlands.
The forested uplands of the Everglades also harbor distinct assemblages of species, dominated by many trees with tropical Caribbean affinities. Ponds occur throughout the Everglades on the lowest elevational sites and are important areas for alligators. Typical aquatic vegetation may include water lilies (Nymphaea spp.) spatter dock (Nuphar advena). Sloughs are found on the wettest sites which experience nearly constant inundation and are underlaid by peat soils. Floating aquatics such as white water lily (Nymphaea odorata) are common and a submerged complex of plants is dominated by bladderwort (Utricularia spp.).
Perhaps the most notable habitat of the Everglades is the sawgrass assembly (in reality sawgrasses are members of the sedge family rather than true grasses; moreover, Jamaica swamp sawgrass (Cladium jamaicense) dominates marshes in terms of abundance and biomass. Sawgrass is well adapted to fire and fluctuating water levels, but is adversely affected by prolonged high surface water levels. On the other hand, wet prairies are dominated by rushes. Portions of the Everglades are also dominated by Muhly grass (Muhlenbergia capillaris).
Also of great biological interest are the diversity of forest types also called tree islands due to being surrounded by a sea of sawgrass. They include swamp forest dominated by red bay (Persea borbonia), pond apple (Annona glabra) forests, pond cypress (Taxodium ascendens) forests, and hardwood hammocks with a variety of tropical species, including palms, that occur only in southern Florida within the USA. The tropical hammocks contain a diverse assemblage of local endemic tree snails of the genus Liguus and tropical butterfly species are also common.
Fire is an important feature in the Everglades, that, along with water flow, assists in maintaining early stage successional habitats. Increases in soil surface elevation leads to greater dominance of hardwoods and scrub.
As with other peninsulas, animal species richness tends to decline in most taxa from the mainland connection to the tip. Southern Florida is no exception, with reduced numbers of vertebrates and invertebrates from north to south. About 70 breeding bird species occur, seventeen species of mammals, 30 species of reptiles, and fourteen species of amphibians. Ponds and creeks are important as dry season refugia for many of these species. Sufficient water levels are crucial for a number of taxa to carry out breeding.
An iconic reptile of the Everglades is the American alligator (Alligator mississippiensis), who prefers the predominant freshwater habitat and eschews brackish waters that can occur near coastlines and even further inland in the dry winter season when freshwater input from rainfall is low. At such times of increasing salinity, the American crocodile (Crocodylus acutus), may be found in the more extensive brackish waters, since this crocodile is tolerant of a wide range of salinity, from freshwater to hypersaline lake water (an extreme case found in one Dominican Republic lake).
Amphibians are represented by the Barking treefrog (Hyla gratiosa), Cuban treefrog (Osteopilus septentrionalis), American green treefrog (Hyla cinerea), Pine woods treefrog (Hyla femoralis), Little glass frog (Pseudacris ocularis), Florida chorus frog (Pseudacris nigrita), Florida cricket frog (Acris gryllus), Pig frog (Lithobates grylio), Cane toad (Rhinella marina), Eastern spadefoot toad (Scaphiopius holbrookii) and the Eastern narrowmouth toad (Gastrophryne carolinensis).
Habitat loss and degradation
After floods in the middle of the twentieth century, a vast area of 2830 square kilometers (km2) was converted to agriculture immediately south of Lake Okeechobee. Today, sugar cane is the most commonly cultivated crop along with truck crops. The effects of fertilizer and pesticide application has reverberated throughout the ecoregion causing widespread degradation. The limestone-based (marl) prairies of the southern Everglades have also been largely converted to agriculture. Eutrophication from agricultural runoff and urbanization has caused the invasion of cattails (Typha sp.).
Most insidious has been disruption of natural water flow through the construction of canals and water management practices. In order to mitigate droughts, water levels were kept abnormally high, leading to a decline in a number of plant communities including sawgrass. Another aspect of water management is excessive drainage of wetlands which affects foraging areas for wading birds, and has led to increased levels of fires which shifts plant succession. The southern prairies have been irreversibly altered as a result of plowing of the substrate and farming. When abandoned, rather than returning to native assemblages, these areas are invaded by exotics or alien species such as the Brazilian pepper tree (Schinus terebinthifolius).
Between 1940 and 1980, the human populations of Dade, Broward, and West Palm Beach Counties increased by 830 percent to 3.2 million people. This rapid population growth has led to the destruction or conversion of the eastern twelve percent of the Everglades.
Habitat alteration and outright loss have endangered a number of plant and animal species. There has been an approximate 90 percent decline in wading bird abundance over the last century. The invasion by the Australian tree Melaleuca has been a minor ecological disaster. Many species of introduced fish and lizards have displaced native species. Fourteen plants and nine vertebrates are Federally listed.
In sum, it is estimated that no more than two percent of the original Everglades ecosystem is truly intact. However, about thirty percent of this unit remains in an altered state that could be restored with proper management described below.
Remaining blocks of habitat
The most important blocks of habitat (all in southern Florida) are:
- Everglades National Park
- Big Cypress National Preserve
- Arthur Marshall Loxahatchee National Wildlife Refuge
- Florida Panther Wildlife Reserves
- Fakahatchee Strand
- Corkscrew Swamp
- Water Conservation Areas
- Biscayne National Park
Degree of fragmentation
Highways and other roads pose a barrier to some species (especially mammals and herpetofauna), but underpasses constructed along portions of Interstate Highway 75 have partially mitigated barrier effects for panthers and other species; in addition to obstructing migration, these roadways have fundamentally created habitat fragmentation. Critical corridors on a micro-scale have been documented. Large blocks of moderately altered habitat (Big Cypress, Everglades) are contiguous or nearly so.
Degree of protection
Within the historic Everglades, there are three conservation areas:
- The Everglades National Park: 2140 km2
- The Big Cypress National Preserve: 222 km2
- The Arthur Marshall Loxahatchee National Wildlife Refuge: 572 km2
Other water management areas are managed in part for biodiversity conservation. Despite protection of a significant portion of the historic Everglades and recognition as an international biosphere reserve, the ecosystem faces severe threats from the impact of surrounding urban sprawl, ecologically unsound water management, agricultural development, invasion of exotic species, and fire.
Types and severity of threats
Assuming restoration efforts will succeed, degradation threats are likely to decline. Otherwise degradation threats will intensify and irretrievably affect this ecosystem. Poaching of deer, alligators, and panthers continues to be a threat.
Suite of priority activities to enhance biodiversity conservation
The restoration of the South Florida/Everglades ecosystem is dependent on a number of strategies and priorities that need to be addressed as the federal and state governments develop a comprehensive plan for restoration of the ecosystem. These include:
- Major changes in water flow, delivery, and management in South Florida intended to benefit Everglades National Park, Florida Bay, the Everglades Water Conservation Areas, and other key areas of the Everglades system
- Improvements in water quality throughout the system, and especially in meeting standards for phosphorus reduction from sugar cane lands in the Everglades Agricultural Area
- Substantial additional land acquisition by both the federal and state government in order to complete the boundaries of existing conservation lands, or to provide the land base necessary to restore more natural water flows through the system
- A very significant investment in state and federal funds for restoration of at least $500 million/year for the next five to six years for research, monitoring, land acquisition, and construction of water delivery and water quality improvement projects.
- Cost-sharing for restoration by the federal government, the state of Florida, and private interests which have contributed to the decline of the Everglades system, including sugar cane growers and other agricultural interests.
The following organizations have been instrumental in planning and executing conservation efforts in the Everglades:
- Everglades Coalition
- Florida Audubon
- Florida Natural Areas Inventory
- National Audubon Society
- National Audubon's Everglades Ecosystem Restoration
- The Nature Conservancy of Florida
References and further reading
- Russell S. Harmon, Carol M. Wicks, Derek C. Ford and William Blaine White. 2006. Perspectives on karst geomorphology, hydrology and geochemistry. 366 pages
- Thomas E. Lodge. 2005. The Everglades Handbook. Understanding the Ecosystem. CRC Press. Boca Raton, FL. ISBN 1-5667-0614-9
- James Watson Porter and Karen G. Porter. 2002. The Everglades, Florida Bay and Coral Reefs in the Florida Keys. CRC Press. 1000 pages
- William Edward Duellman. 1999. Patterns of distribution of amphibians: a global perspective. JHU Press. 633 pages
- Fred Hal Sklar and Arnoud van der Valk. 2002. Tree islands of the Everglades. Springer. 541 page
- Edward R. Ricciuti. 1997. Natural History of North America. 224 pages
Additional information on the Everglades
- To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
Disclaimer: This article contains certain information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.