Chapter 50
Ecological Subregions of the United States



Everglades Province

One Section has been delineated in this Province:

This Section is located in southern Florida and has an area of about 7,800 mi2 (20,200 km2).

Section 411A--Everglades

Geomorphology. This Section is in the Coastal Plains geomorphic province. The predominant landform is a flat, weakly dissected alluvial plain formed by deposition of marine sediments onto a submerged, shallow continental shelf, which was later exposed by sea level subsidence. Along the coast, fluvial deposition and shore-zone processes are active in developing and maintaining beaches, swamps, and mud flats. Elevation ranges from sea level to 80 ft (25 m). Local relief ranges from 0 to 10 ft (3 m). Lithology and Stratigraphy. Rocks were formed during the Cenozoic era. O\"olitic limestone, which underlies much of south Florida, formed during the Tertiary period and consists of marine deposits that are calcareous and highly fossiliferous. Quaternary period strata consist of poorly consolidated sands and gravels.

Soil Taxa. Soils are mostly Saprists and Fibrists. Medisaprists occur over shallow limestone bedrock. Medifibrists and Medisaprists formed over mineral parent materials. Psammaquents and Ochraqualfs have developed where limestone rocks are at greater depths. Along the coasts are Sulfihemists and Sulfaquents. Soils in this Section have a hyperthermic temperature regime and are mostly aquic in moisture regime. Most soils inland from the coasts are poorly drained, shallow, and moderately textured. Some coastal soils are deep sands that are well drained or excessively drained.

Potential Natural Vegetation. K\"uchler classified five potential communities: Everglades ({\it Mariscus, Magnolia-Persea}); mangrove, cypress savanna, and sub-tropical pine forest. This Section is dominated by two principal potential natural communities adapted to hydric conditions: an extensive treeless savanna (the Everglades) on the eastern side of the Section, and forested woodlands (the Big Cypress Swamp) on the western side. The Everglades is a shallow, broad (60 mi, 95 km) river with freshwater flowing southward from Lake Okeechobee to the Gulf of Mexico. Physiognomy of vegetation varies by duration of inundation and amount of salt content. Vegetation includes: grasses in permanently submerged freshwater habitats; trees in dry to intermittently flooded fresh water habitats; and shrubs to small trees in saltwater estuary habitats. Predominant vegetation of flooded freshwater habitats includes sawgrass (actually a sedge), swamp lily, and spatterdock; on islands of slightly higher elevation (hammocks), trees include slash pine, royal palm, gumbo limbo, and strangler fig. Epiphytes are common. Big Cypress Swamp, and other adjacent areas to the north, are characterized by intermittently flooded freshwater habitats with very poor drainage that are dominated by cypress; oaks and magnolias occupy better drained areas. Poorly drained soils along the east coast, and farther inland along the west coast, are dominated by south Florida slash pine. Sand pine, with scrub oak and saw palmetto understory, occupies excessively drained, deep sands. Both south Florida slash and sand pine are well adapted to an environment of frequent fire. Coastal areas influenced by saltwater tidal zones are occupied by successive zones of vegetation, from freshwater to saltwater environments, of button mangrove, black mangrove, and red mangrove, respectively. Other species common to this tropical environment include Florida fishpoison-tree, Bahama lysiloma, royal poinciana, tamarind, shortleaf fig, Florida royalpalm, Jamaica thatchpalm, and oxhorn bucida. Key West Cephalocereus, a tree-sized member of the cactus family, occurs in thin, dry soils of the Florida Keys. Exotic species are creating a threat to native species. For example, the cajuput, or bottle-brush tree, a native of Australia has been planted widely as an ornamental and is now invading the Everglades National Park. Also, the water hyacinth, a free-floating Brazilian herb, clogs waterways.

Fauna. Freshwater habitats are occupied by woodstork, bluegill, crayfish, Florida gar, largemouth bass, purple gallinule, alligator, ibis, zebra butterfly, Everglades kite, and apple snail. Characteristic fauna of hammocks are tree snails, barred owl, white-tailed deer, and Florida panther. In saltwater habitats, typical fauna include great white heron, American crocodile, loggerhead turtle, manatee, pink shrimp, mangrove snapper turtle, blue crab, coon oyster, brown pelican, osprey, roseate spoonbill, and southern bald eagle. Key deer are restricted to several small islands on the southern coast. Many birds of this Section occur over broader areas of Florida or south into islands of the Caribbean Sea. These include gray kingbird, blue-gray tanager, swallow-tailed kite, Caspian tern, stilt sandpiper, magnificent frigatebird, brown noddy, smooth-billed ani, white-crowned pigeon, and short-tailed hawk. Geckos include yellow-headed, indigo-Pacific, and reef. Crested, bark, and brown anoles are common. There are many introduced species of fauna. At least six species of the Everglades environment are threatened or endangered.

Climate. Annual precipitation ranges from 50 to 64 in (1,270 to 1,620 mm). About one-third of this total occurs during the fall and winter dry season. Mean annual temperature is from 72 to 77 oF (22 to 25 oC). The frost-free growing season lasts for 330 to 365 days. Key West, an island about 100 miles south of the mainland, has no record of freezing temperature.

Surface Water Characteristics. Other than precipitation, the source of most surface water in the Everglades is Lake Okeechobee, about 750 mi2 (1,940 km2) in area, immediately north of this Section. Most waterways are canals that were built to carry a moderate to high volume of water at very low velocity. The water table is high in many areas, resulting in poor natural drainage and abundance of wetlands. A poorly defined drainage pattern has developed on this landscape, which is relatively young and weakly dissected. Palustrine systems having seasonally high water levels are abundant. This Section adjoins the West Indian Marine and Estuarine provinces.

Disturbance Regimes. Hurricanes are probably the most widespread form of natural disturbance, followed by infrequent fires during the winter dry season. Fire consumes irregular areas of organic soils, which fill with water during the wet season to make shallow lakes.

Land Use. Much of the land along the east and west coasts has been cleared of natural vegetation, originally for agriculture, but more recently for urban development. This Section contains the Everglades National Park, the Seminole and Miccosukee Native American reservations, and several national wildlife refuges.

Cultural Ecology. The mild, almost tropical-like climate has been a major factor in the rapid development of south Florida, a Section of relatively few natural resources. Following initial settlement by Archaic peoples, the Seminoles became the first modern inhabitants of the Everglades as they retreated from settlers and soldiers in more northern areas. A project to drain the Everglades was initiated in the early 1900's to allow cultivation of vast areas of fertile, organic soils for winter vegetables. During this time, extension of a railroad into south Florida along the east coast contributed to several cycles of land speculation followed by depression. During the mid century, populations increased due to agricultural crops and a service-based economy related to expanded tourism. A narrow band of better drained soils along the east and west coasts developed rapidly into almost continuous metropolitan areas. During the late 1900's, populations again surged as a result of retirement re-locations from northern states. Increased populations place heavy demands on freshwater resources, especially during drought years, at the expense of maintaining water flows from Lake Okeechobee southward into the Everglades. Development of large sugar cane fields south of Lake Okeechobee also increased nutrient levels of water runoff and caused additional stress on natural aquatic environments. Introduction of exotic plant and animal species has stressed native populations of some species. Relatively few of the current human population is native to the Section, and previous attitudes have been more sympathetic toward development than conservation. However, increased attention is now being given to restoring historic patterns of water levels and movement in the Everglades, especially since the Everglades National Park was established in 1947.

Compiled by Southeastern Forest Experiment Station. Sedges and grasses dominate much of the shallowly inundated Everglades; shrubs grow on islands. White-tailed deer are common.}