AMERICA’S SUBTROPICAL WONDERLAND
[Everglades] may not be our largest national park (that honor belongs to Wrangell-St. Elias in Alaska), but it is certainly the wettest. During and after the rainy season, when not only the [mangrove] [swamp] but also the sawgrass prairie is under water, most of the park abounds in fish and other water life, and even the white-tailed deer leads a semi-aquatic existence.
Despite the fact that it is low, flat, and largely under water, [Everglades] is a park of many environments: shallow, key-dotted Florida Bay; the coastal prairie; the vast [mangrove] forest and its mysterious waterways; cypress [swamps]; the true everglades—an extensive freshwater [marsh] dotted with tree islands and occasional ponds; and the driest zone, the pine-and-hammock rockland.
The watery expanse we call “[everglades],” from which the park gets its name, lies only partly within the park boundaries. Originally this river flowed, unobstructed though very slowly, southward from Lake Okeechobee more than 100 miles to Florida Bay. It is hardly recognizable as a river, for it is 50 miles wide and averages only about 6 inches deep, and it creeps rather than flows. Its source, the area around Lake Okeechobee, is only about 15 feet above sea level, and the riverbed slopes southward only 2 or 3 inches to the mile.
As you can see by the maps on pages [2] and [3], the works of man have greatly altered the drainage patterns and the natural values of south Florida, and you can imagine how this has affected the supply of water—the park’s lifeblood.
The park’s array of plants and animals is a blend of tropical species, most of which made their way across the water from the Caribbean islands, and species from the Temperate Zone, which embraces all of Florida. All of these inhabitants exist here through adaptation to the region’s peculiar cycles of flood, drought, and fire and by virtue of subtle variations in temperature, altitude, and soil.
HISTORIC DRAINAGE PATTERNS OF SOUTH FLORIDA
DRAINAGE PATTERNS OF SOUTH FLORIDA TODAY
PLANT [COMMUNITIES] OF [EVERGLADES] NATIONAL PARK
The horizontal distance represented on this diagram, from the Pineland to Florida Bay, is 15 miles. With a greatly exaggerated vertical scale, the difference between the greatest elevation of the pine ridge and the bottom of the Florida Bay [marl] bed is only 14 feet.
FLORIDA BAY (SALT WATER) MUD BANK [KEY] COASTAL PRAIRIE [MANGROVE] [SWAMP] (BRACKISH) BUTTONWOOD LEVEE TREE-ISLAND GLADES (FRESH WATER) BAYHEAD CYPRESS HEAD WILLOW HEAD HARDWOOD [HAMMOCK] PINE AND HAMMOCK RIDGE
Underlying the entire park is porous [limestone] (see glossary), which was deposited ages ago in warm seas that covered the southern part of today’s Florida peninsula. Over this limestone only a thin mantle of [marl] and [peat] provides soil for rooting plants.
Some of the park’s [ecosystems] (see glossary) are extremely complex. For example, a single jungle [hammock] of a dozen acres may contain, along with giant live oaks and other plants from the Temperate Zone, many kinds of tropical [hardwood trees]; a profusion of vines, mosses, ferns, orchids, and air plants; and a great variety of vertebrate and invertebrate animals, from tree snails to the white-tailed deer.
Pine Rockland
Entering the park from the northeast, you are on a road traversing the pineland-and-hammock “ridge.” This elevated part of the South Florida [limestone] bedrock, which at the park entrance is about 6 feet above sea level, is the driest zone in the park. Pine trees, which will grow only on ground that remains above water most of the year, thrive on this rockland.
There is another condition essential to the survival of the pine forest in this region—fire. We usually think of fire as the enemy of forest vegetation; but that is not true here. The pines that grow in this part of Florida have a natural resistance to fire. Their thick, corky bark insulates their trunks from the flames. And strangely enough the fire actually seems to help with pine reproduction; it destroys competing vegetation and exposes the mineral soil seedlings need. If there has been a good cone crop, you will find an abundant growth of pine seedlings after a fire in the pinelands.
What would happen if the pinelands were protected from fire? Examine a pine forest where there have been no recent fires. You will note that there are many small hardwood (broadleaved) trees growing in the shade of the pines. These hardwoods would eventually shade out the light-demanding pine seedlings, and take over as the old pines died off. But under normal conditions, lightning-caused fires sweep at fairly frequent intervals through the pineland. Since the hardwoods have little resistance to fire, they are pruned back.
Before this century, fires burned vast areas. The only barriers were natural waterways—[sloughs], lakes and ponds, and [estuaries]—which retained some water during the rainless season when the rest of the glades and pinelands dried up. Old-timers say that sometimes a fire would travel all the way from Lake Okeechobee to the coastal prairie of Cape Sable (see [page 2]). In the pine forest, any area bypassed by these fires for a lengthy period developed into a junglelike island of hardwoods. We call such stands “[hammocks],” whether they develop in the pine forest or in the open glades. On the [limestone] ridge, the hammocks support a [community] of plants and animals strikingly different from the surrounding pine forests.
PINE AND [HAMMOCK] RIDGE
(elevation: 3 to 7 feet above sea level)
SAWGRASS GLADES PINELAND HARDWOOD [HAMMOCK] PINELAND 1 SOUTH FLORIDA SLASH PINE 2 SAW-PALMETTO 3 COONTIE 4 SAW-PALMETTO AFTER FIRE
With the opening up of south Florida for farming and industry, man’s works—particularly roads and canals—soon crisscrossed the region, forming barriers to the spread of the fires. Suppression of fire by farmers, lumbermen, and park managers also lessened their effect. Thus the hardwoods, which previously had been held back by fire, tended to replace the pines. And although the park was established to preserve a patch of primitive subtropical America as it was in earlier centuries, the landscape began to change.
Continued protection of the park from fire would in time eliminate the pineland—a plant [community] that has little chance to survive elsewhere. So, in [Everglades] National Park, Smokey Bear must take a back seat: park rangers deliberately set fires to help nature maintain the natural scene. Thus, as you drive down the road to Flamingo, do not be shocked to discover park rangers burning the vegetation. The fires are controlled, of course, and the existing [hammocks] are not destroyed.
When you visit the park take a close look at the pinelands [community]. Notice, as you walk on the manmade trail through the pine forest, that the ground on either side of you is extremely rough. The [limestone] bedrock is visible everywhere; what soil there is has accumulated in the pits and potholes that riddle the bedrock. The trees, shrubs, grasses, and other plants are rooted in these pockets of soil.
The [limestone] looks rather hazardous to walk on—and it is. You must be careful not to break through a thin shell of rock covering a cavity. This pitted, honeycombed condition is due to the fact that the limestone is easily dissolved by acids. Decaying pine needles, palmetto leaves, and other dead plant materials produce weak acids that continually eat away at the rock.
If a fire has passed through the pineland recently, you may notice that while most of the low-growing plants have been killed, some, such as the saw-palmetto, are sending up new green shoots. The thick, stubby stem of the palmetto lies in a pothole, with its roots in the soil that has accumulated there; even in the dry season the pocket in the [limestone] remains damp, for water is never very far below the surface in this region. When fire kills the top of the plant, the stem and roots survive, and the palmetto, like the pine, remains a part of the plant [community].
A number of other plants of the south Florida pinelands have adapted to the conditions of periodic burning. Coontie (a cycad, from the underground stems of which the Indians made flour) and moon vine (a morningglory) are among many you will see surviving pineland fires severe enough to result in the death or stunting of the hardwood seedlings and saplings.
Sometimes we forget that fire—like water, wind, and sunlight—is a natural force that operates with the others to influence the evolution of plants as well as to shape the landscape.
The pineland, like other plant [communities], has its own community of animals. Some of its residents, such as the cotton mouse, opossum, and raccoon, are found in other communities of the park, too.
Some of the pineland animals, however—pine warbler, reef gecko, and five-lined skink, for example—are particularly adapted to this [environment]. These lovers of sunlight are dependent, like the pine forest, on the occasional natural or manmade fires that hold back the [hardwood trees].
The pine rockland is quite different from the other plant-and-animal [communities] you will see as you drive through the park: it is the only ecosystem you can explore on foot in any season. Other parts of the park are largely flooded during the wet season. Elevated boardwalks have been provided in some of these areas to enable you to penetrate them a short distance from the road.
As you will see, fire plays an important role in some of the other [Everglades] [communities], too.
Tree-island Glades
(elevation: 1 to 3 feet above sea level)
BAYHEAD WILLOW HEAD SAWGRASS PINE DWARF CYPRESS FOREST ALLIGATOR HOLE CYPRESS HEAD
PIG FROG
one-third life size
GREEN TREEFROG
one-third life size
SQUIRREL TREEFROG
color variation
Beyond the pinelands the road, having descended some 2 feet from the park entrance, brings you into the true [everglades]—the river of grass, or, as the Seminoles call it, Pa-Hay-Okee (grassy waters). To the eye, the glades look like a very flat, grassy prairie broken by scattered clumps of trees. During the dry season (winter) it is in fact a prairie—and sometimes burns fiercely. The dominant everglades plant is sawgrass (actually not a grass but a sedge). The tree islands develop in both high and low spots of the glades terrain. In this unbelievably flat country, small differences in elevation—measured in inches rather than feet—cause major differences in the plantlife: tropical hardwoods on the “mesas,” and [swamp] trees in the potholes.
A spot in the glades where the [limestone] base is elevated just 2 feet will be occupied by a small forest of tropical hardwoods and palms—a “[hammock]” much like those of the pinelands. A low spot—just a few inches below the general level of the limestone base—will remain wet even in the relatively rainless winter when the sawgrass becomes tinder dry. This sloughlike depression will support a stand of baldcypress, called a “cypress head.” Other tree islands, called bayheads and willow heads, develop in many places where soil and [peat] accumulate.
Step from the sawgrass glades into one of these [hammocks] or heads; you will find yourself in another world. You cannot know the park until you have investigated these plant-and-animal [communities] so distinct from the surrounding [marsh] yet so much a part of it. As you drive through the park, look for the trails provided to give you easy access into the interior of the tree islands.
Also characteristic of the glades are the [sloughs]—channels where the glades water, generally a thin, seemingly motionless sheet, is deeper and has a noticeable current. The sloughs support a rich plantlife and attract a variety of animals, particularly during the dry season when the water level drops below the shallow glades bottom. Animals that live in the glades when they are under water must migrate or [estivate] (see glossary) if they are to survive the rainless months. Many migrate to the sloughs, the best known of which is Taylor Slough, where the elevated Anhinga Trail enables you to walk over the water and observe the wildlife.
Fire is an important factor in the [ecology] of the tree-island glades, just as it is in the pineland. Here, too, artificial barriers such as canals and roads have hindered the spread of natural fires. There is some evidence that tree islands were scattered more thinly over the sawgrass prairie a half-century ago, when a single fire might wipe out scores of them and destroy much of the bed of [peat] that provided a foothold for them. A bird’s-eye view of the glades region today shows many tree islands that have been established in recent decades. But park rangers are now utilizing controlled fires in the glades as well as in the pineland. This tends to prevent new tree islands from taking hold, and thus helps maintain the natural [everglades] landscape.
Driving over the glades toward Florida Bay, you come to a sign reading “Rock Reef Pass—Elevation 3 Feet.” The road then traverses the so-called dwarf cypress forest. The forest is an open area of scattered, stunted baldcypress growing where [marl] (which, unlike [peat], does not burn) has accumulated in small potholes dissolved in the [limestone]. These marl potholes provide a foothold for the dwarf cypresses in an area that is spotted with cypress heads containing much larger trees. Many of the dwarf cypresses are more than 100 years old, while tall cypresses in the heads may be less than 50 years old. These anomalies can be attributed to varying soil depths and water levels and to the effects of fire.
Before you reach the limit of the fresh-water [marsh] you will come to a side road leading to Mahogany [Hammock]. (A good foot trail makes it easy to explore this hardwood jungle island.) Just beyond, you will notice the first red [mangroves]. Small and scattered in this zone, they are a signal that you are approaching a strikingly different plant-and-animal [community], the mangrove [swamp].
[Mangrove] [Swamp]
(elevation: sea level to 1 foot above sea level)
PRAIRIE SEDGES
BAY JAMAICA DOGWOOD GUMBO-LIMBO MAHOGANY PRAIRIE SEDGES BUTTONWOOD WHITE-MANGROVE OSPREY NEST BLACK-MANGROVE RED-MANGROVE (very dense growth) [ESTUARY]
BONEFISH Comes in with the tide to feed on crabs and mollusks in shallow water
FLORIDA HORN SHELL Lives in shallow water and feeds upon [algae] and other aquatic plants
’COON OYSTER A small (1½″) oyster that lives attached to the roots of [mangroves]
The southward-creeping waters of the glades eventually meet and mingle with the salty waters of the tidal [estuaries]. In this transition zone and along the gulf and Florida Bay coasts a group of trees that are tolerant of salty conditions, called “[mangroves],” form a vast, watery wilderness. Impenetrable except by boat, it occupies hundreds of square miles, embracing both the shifting zone of [brackish water] and the saltier coastal waters.
Several kinds of trees are loosely called “[mangroves].” The water-tolerant red mangrove grows well out into the mudflats and is easily recognized by its arching stiltlike roots. Black-mangrove typically grows at levels covered by high tide but exposed at low tide, and it is characterized by the root projections called pneumatophores that stick up out of the mud like so many stalks of asparagus growing in the shade of the tree. White-mangrove has no peculiar root structure and grows, generally, farther from the water, behind the other trees. Sometimes all three are found in mixed stands.
This [mangrove] wilderness, laced by thousands of miles of estuarine channels (called “rivers” and “creeks”) and broken by numerous bays and sounds, is extremely productive biologically. The brackish zone is particularly valuable as a nursery ground for shrimp. The larvae and young of these marine crustaceans and of other marine animals remain in this relatively protected [environment] until they are large enough to venture into the open waters beyond the mangroves.
THE [MANGROVE] [SWAMP] AND THE COASTAL PRAIRIE
The shrimp represent a multi-million-dollar industry, and the sports-fishing business of the area is said to exceed that by far. Both would suffer if any damage occurred to this ecosystem. The greatest danger is the alteration in the flow of fresh waters from the glades and cypress [swamps] that occurs when new canals are built and land is drained for cultivation or development. The flow carries with it into the [estuaries] organic materials from the rich glades ecosystem; these supplement the vast quantities of organic matter derived from the decay of red [mangrove] leaves. Thus, a reduction in the amount of nutrient-laden fresh water flowing into the mangrove region will affect the welfare of the ecosystem, and indirectly the livelihood or recreation of many persons.
The productive zone of [brackish water] varies in breadth according to the flow of fresh water. In the wet summer it moves seaward as the flow of fresh water from the glades pushes the tides back. In the drier winter the bay and gulf waters move inland and the brackish zone is quite narrow. The drainage and canal-building operations in south Florida can be extremely disruptive here, since too little, or too much, fresh water flowing into the [estuaries] can interfere with their productivity.
Natural disasters such as hurricanes can also bring about great changes in the [mangrove] ecosystem. Yet biologists do not necessarily view the destruction of mangroves by hurricanes as catastrophic. The hurricanes have been occurring as long as the mangroves have grown here and are part of the complex of natural forces making the region what it is.
Fire does not seem to be a problem in the [mangrove] wilderness. The trees themselves are not especially fire-resistant, but it is not uncommon to see a glades fire burn to the edge of the mangroves and stop when it runs out of fine fuel.
The [mangrove] wilderness is a mecca for many park visitors. Sportsmen take their motorboats into the bays and rivers to challenge the fighting tarpon. Bird lovers seek the roosts and rookeries of herons and wood storks. Canoeists, the only ones able to explore the secret depths, are drawn by the spell of labyrinthine channels under arching mangrove branches. Here, in a wilderness still thwarting man’s efforts at destruction, one experiences a feeling of utter isolation from the machine world.
But the relentlessly rising sea of the past 10,000 years has belittled drought, fire, hurricane, and frost as it slowly inundated this land 3 inches each hundred years. In compensation, the [mangrove] forest adds [peat] and rises with the sea. The sawgrass [marshes] retreat, and the mangrove ecosystem prevails essentially unchanged.
APPLE MUREX
A carnivorous mollusk that feeds on oysters.