The Everglades: America's Most Threatened Ecosystem - Lecture Note - Completely Remote Sensing tutorial, GPS, and GIS -
The Everglades: America's Most Threatened Ecosystem

The Great State of Florida - the Sunshine State - with nearly 16 million residents, grows each winter as "snow birds" from the North pour into the state to enjoy often tropical-like weather and marvelous amenities for vacationers. Some, liking the lifestyle, come back to settle. (This invasion of resettlers assumes a fair tolerance for hurricanes.) But this influx, on top of the previous permanent residents, is steadily putting a strain on both people facilities and natural ecosystems. Nowhere is the long term outlook more troubling than that last refuge of the tropics in the U.S. - the Everglades. This huge area of water and vegetation, almost untouched by man, is the most fragile and susceptible ecosystem in this part of America. The problem is the insatiable desire of developers for more land to house more people and establish recreational areas as well as farmland taking advantage of fine soils. But a major decision has been made by federal and state governments, and environmental groups (the "Greens") to reverse adverse land management trends and restore the pristine state of the Everglades subtropical wilderness. This page will be a "case study" in examining these efforts and in showing how remote sensing plays a major role.

To see the Everglades as part of the entire Florida peninsula, look first at this Landsat mosaic:

Landsat mosaic of southern and central Florida.

The Everglades occupy much of the southern tip of the state. Miami (dark pink in image) lies near the southeastern tip of coastal Florida. The large body of inland water is Lake Okeechobee, which in a sense was once the north end of the Everglades and still strongly influences the drainage patterns to the south. The entire peninsula is geologically a terrane that was added to the rest of North America in the last 50 million years. It is made up of ancient crystalline rocks topped by mainly limestones deposited in the Cenozoic Era.

From that regional view, we next show a Landsat-3 subscene which covers part of the Everglades and the urban strip on the Atlantic Ocean.

Landsat-3 1978 subscene in false color showing the Everglades and the Miami-Fort Lauderdale strip.

Much of the Everglades is dark because most of its area is covered with water (adds black to the standard false color version). Areas in strong red at its south end are mostly mangrove swamps. Small elongate areas are "Tree Islands", slight rises above water that support hardwoods and other vegetation. Look for several red lines crossing the Everglades: these are drainage canals that host active vegetation. The eastern coastal area of this part of Florida is built on limestone bedrock, topped with soils and sands, and is now one continuous metropolitan area that includes Miami and Fort Lauderdale (see page 4-2). More features in this scene will be discussed elsewhere on the present page.

We now want to further familiarize you with what the Everglades are all about. You have a choice: open these online Everglades Summary and ParkVision sites and/or just keep reading here.

First, we will consider its pre-Columbian history. Archeaological evidence suggest humans may have inhabited the lands, shorelines, and wetlands as early as 10000 years ago. But the initial indications of a sophisticated tribal community goes back to about 100 A.D. with the presence of the Calusa (Caloosa) People (one of many populations in North America that are lumped together as Natives). They spread over much of present-day Florida but were concentrated mainly on the southwest coast around today's Fort Myers and Naples. They were builders of artificial islands and inland mounds made from oyster and other molluscan shells (their principal food). On these were established small villages. An aerial photo shows one elongate shell Mound

An elongate shell mound (towards right) near the Everglades.

The population center for the Calusa was the Ten Thousand Islands area south of Naples, once part of the Everglades.

Some of the many small islands off the southwestern Gulf Coast of Florida.

The most ambitious Calusa project was the building of a 125 acre island that rises from 25 to 40 feet above today's sealevel. The island had homes, religious buildings (the Calusa were in to human sacrifice), and water storage facilities. This was probably their capital "city", but today Mound Key is a National historical site, which shows only the foundations of some dwellings:

Mound Key, a Calusa stronghold.

The Calusa culture was fairly advanced, comparable to the Mayans, as demonstrated by this rital mask used in religious ceremonies.

Calusa mask.

The Calusa persisted until the coming of the Europeans in the 16th Century. They shared Florida with other tribes such as the Tequesta. The Spaniard explorers eventually wiped them out, but not before a Calusa arrow had killed Ponce de Leon, thus cutting short his effort to find the Fountain of Youth in Florida.

The Indian population of Florida went into sharp decline after the Spanish took over. The best known of modern tribes is the Seminoles. These originally lived in Georgia and elsewhere but were driven south all the way to the Everglades by Gen. Andrew Jackson and others. Today about 10000 still remain in the state. Some live in small settlements in and around the Everglades.

A Seminole village in the Everglades.

Next, to establish the geography of the Everglades, look at these three maps:

Regional map (left) and more detailed map of the Everglades (right).
Another version of a map concentrating on the Everglades.

There is an even more detailed map that focuses on the Everglades National Park but to reduce it to fit this page would make the smaller print unreadable. So, you have the option of seeing the larger version on this extra page 8a.

From the above it is evident that the Everglades includes large areas outside the Everglades National Park. The Park was established in 1934, largely through the dedicated efforts of an architect, Ernest Coe, whose passion for this extraordinary wilderness made him an effective lobbyist. Since then the entire ecosystem has been in jeopardy from the development of Florida for its residents and visitors. Two maps indicate the trends.

Florida landcover maps for the years 1900 and 1992.
The loss of Everglades types of landcover between 1900 and 1999.

Both maps are almost self-explanatory. Florida has altered much of its natural land cover types to farmland, grazing land, and urban/suburban units over the last 100 years. In the last 100 years the natural swamps of southern Florida that include the Everglades have shrunk by about 50%. This is a loss of about 2.9 million acres. There is another way to view these changes. The U.S. Geological Survey, one of the agencies involved in protecting the Everglades, has produced an "artificial" Landsat image of what the land cover was like in 1850. That image (left) is placed next to a recent (2000) actual Landsat image. Compare the differences:

Synthetic space image of land use 1850; note that the Atlantic coastal region is largely made up of sandy cover on top of limestone; USGS project . Actual imagery of land use 1995

The reasons for the Everglades existence are largely tied to geology, climate, and drainage. Southern Florida is almost entirely capped with limestones that are more easily eroded than most other rock types. Sinkholes, drainage channels, and outliers making slightly higher ground are found in the Everglades and into central Florida. Here is a view in the Everglades showing limestone outcropings.

Limestone outcrops in the Everglades; in places the limestone can be described as a marl or as a coquina.

The climate factor is the prevailing hot and humid conditions that promote vegetation typical of subtropical marshlands and forests. We will examine examples of this below. The dominant factor has been the pattern of drainage from pre-colonial times that has since been largely altered. Lake Okeechobee is a large depression (developed from dissolved limestone) that has been filled by streams such as the Kissammee River which begins south of Orlando. From this lake water for eons has flowed in a series of streams, some riverlike, others just sheetflow across the lowlands to the south. Water flow, at current rates southward of about 100 ft (30 meters) a day, extends over most of the Everglades to depths of a few inches up to six feet. So the Everglades is in effect a grandiose wetlands with 1-2 feet of peat below and limestone bedrock beneath that. In effect, the water flow is almost akin to a single, very broad and shallow river, which can be seen at the surface but is also hidden in large part by vegetation. This is a typical view of the channel system; most of the vegetation is sawgrass.

Aerial view of typical Everglades with the land (hammocks) between stream channels being a mix of cypress, hardwoods, and sawgrass.

Before major development the general pattern of water flow in southern Florida was this ("current" refers to both flow direction and to "contemporary"):

Left: Water flow patterns in southern Florida before extensive land reclamation for farming and urban centers; Right: Present day water flow; see text below..

Lake Okeechobee has been the key to the changes in the regional drainage system. Suffice for now to say that the drainage system from Okeechobee south has undergone major alteration. The entire lake has a restraining wall or levee that allows control over the drainage outlets. This wall, 143 miles in length, was built by the U.S. Corps of Engineers in the early 1940s in response to flooding caused in a 1928 hurricane which carried excessive water into the Everglades and burst protective levees next to the coastal strip (several thousand people drowned). Made of earth and rock, the Okeechobee levee is 30-40 feet above normal lake level and 20 feet wide at the top. Several canals have been built in the 1960s (the water they receive passes through a lock system), trending southeast and south, from the lake country into the Everglades to aid in carrying off excess water. Now, about 1.7 billion gallons a day are released from Okeechobee in a controlled manner. As a planned by-product, this produced land for farming and metropolitan use. But, this re-engineering of the drainage has significantly modified the natural state of the Everglades so that it now receives much less water. And parts of this water are being polluted by the inhabitants surrounding the Everglades.

The engineering features around Lake Okeechobee; the level is shown in white.
The earthen levee with Lake Okeechobee in the background
One of the locks feeding a canal.

Now, instead of unrestricted flow southward into the Everglades, and thus fundamentally modifying its hydrology that preserves much of its natural ecosystem, Okeechobee waters are largely redirected to the Gulf Coast at Fort Myers via the west-flowing Caloosahatchee River and east to the Atlantic via the St. Lucie, West Palm Beach, Hillsboro, North New River, and Miami canals. The present system of natural and canal drainage is superimposed in blue on a Landsat mosaic:

Drainage rivers and canals in southern Florida.

Reclaimed land immediately south of Lake Okeechobee (see Landsat images) is used for agriculture - principally sugar cane and citrus groves.

Sugar cane fields and orchards just south of Lake Okeechobee.

Both in the past and now water released from the southern dikes at Okeechobee and surviving natural drainage flows through the Everglades as sheetflow and rivers. Most of the Everglades has water at its surface which will be moving at various rates towards the coast. The main flow routes are called "sloughs" (pronounced "slews"), similar to the bayous of Louisiana, that largely are covered in vegetation ("rivers of grass"). The largest, Shark River Slough, is shown here in a map and as an aerial view (water underlies the vegetation but is hard to see).

The location of Shark River Slough.
Aerial view of Shark River Slough.

But despite these drainage perturbations in the original Everglades, most of the flora and fauna are still preserved. Let's look at a series of pictures that describe the typical members of this habitat. First, a cartoon summarizing the principal vegetation types in relation to sealevel.

Vegetation habitats in the Everglades.

The next two views show vistas in which the dominant vegetation - sawgrass - makes up large segments of the eastern Everglades. This underlies the appellation given to the Everglades as "The River of Grass":

Sawgrass in the Everglades; brown because it is winter
Another view of sawgrass evident in the growing season.

These two photos show the grass and reeds in close-ups.

Close-up of Sawgrass and reeds, showing their growth in the shallow water flowing through the Everglades.
Sawgrass and other vegetation can reach considerable heights.

Note in the two images below the presence of isolated trees in clumps. Often referred to as hammocks, these "Tree Islands" are characteristic of much of the Everglades. On a grander scale, hammock groves are separated by water too deep to support much vegetation:

Hardwoods hammocks scattered throughout water collected in continuous slow-flowing streams.
Another look at Tree Islands.

Sometimes the stream flow actually organizes into channels:

Rivers within the Everglades.

Stands of southern pines are found in areas above water level. They often are associated with palmettos and other bladed plants.

Pines and palmettos in the Everglades

Cypress forests occur both scattered in the upper Everglades and as a dominant vegetation type in the Big Cypress National Preserve. The next pair of pictures show Cypress trees in summer, and the third, an aerial view of Tree Islands supporting Cypress stands.

Cypress stand in summer within a water base.
Cypress in drier land.
Tree islands populated by Cypress trees

One of the most distinctive tree families in the Everglades, found mostly in the coastal and southern parts, are the Mangroves. Mangroves, like Cypresses, grow in permanent water. These trees come in several varieties, as shown in the next two photos.

One species of Mangroves
Another type of Mangrove.