PLANT-AND-ANIMAL COMMUNITIES |
To know Everglades, you must become acquainted with some of its diverse communities. The physical conditions determining the existence of a particular community may seem subtle—just a few inches difference in elevation, or an accumulation of peat in a depression in the limestone bedrock, for example. But often, the change in your surroundings as you step from one community to another is startling—for it is abrupt and complete. In Everglades, the dividing line between two habitats may separate an almost entirely different association of plants and animals. Use the trails that have been laid out to help you see the communities. They make access easy for you; the rest is up to you. Be observant: notice the stemlike root of a saw-palmetto in a damp pothole of the pineland; look closely at the periphyton that plays such an important role in the glades food chain. Note the difference in feeding methods of wading birds; each species has its own niche in the habitat. Most of all, get into the habit of thinking of each animal, each plant, as a member of the closely woven web of life that makes up an integrated community. Tropical Hardwood Hammock Generally, in south Florida, hardwood hammocks develop only in areas protected from fire, flood, and saline waters. The land must be high enough (1 to 3 feet above surrounding levels) to stand above the water that covers the glades much of the year. The roots of the trees must be out of the water and must have adequate aeration. In the park, these conditions prevail on the limestone “ridge” (elevation of which ranges from 3 to 7 feet above sea level) and some spots in the glades region. On the limestone ridge, in areas bypassed by fires for a long period, hammocks have developed. Pines grow in the surrounding areas, where repeated fires have held back the hardwoods. The moats that tend to form around glades hammocks, as acids from decaying plant materials dissolve the limestone, hold water even during the dry season; the moats thus act as barriers protecting the hammock vegetation from glades fires. When the white man took over southern Florida, these hammocks were luxuriant jungle islands dominated by towering tropical hardwoods and palms. Stumps and logs on the floors of some of the remaining hammocks, attesting to the enormous size of some of the earlier trees, are sad reminders of the former grandeur of the hammocks. While most of south Florida’s hammocks have been destroyed, you can still see some fine ones protected in the park. At Royal Palm Hammock, near park headquarters, Gumbo Limbo Trail winds through a dim, dense forest with welcome coolness on a hot day. Stepping into a jungle hammock from either the sunbathed glades or the open pine forest is a sudden, dramatic change. The contrast when you enter Gumbo Limbo Trail immediately after walking the Anhinga Trail is striking. While the watery world of Anhinga is dominated by a noisy profusion of wildlife, the environment of Gumbo Limbo will seem to be a mere tangle of vegetation. But the jungle hammock, too, has its community of animals—even though you may notice none but mosquitoes. Many of its denizens are nocturnal in their habits, but if you remain alert you will observe birds, invertebrates, and perhaps a lizard. TREE SNAILS
There are 52 color forms of Liguus fasciatus found in south Florida. Liguus fasciatus pseudopictus The trees that envelop you as you walk on Gumbo Limbo Trail are mostly tropical species; of the dominant trees, only the live oak (which grows as far north as Virginia) can be considered non-tropical. Under oaks and tropical bustics, poisonwood, mastics, and gumbo-limbos grow small trees such as tetrazygia, rough-leaf velvetseed, and wild coffee, a multitude of mosses and ferns, and only a few species of shade-tolerant flowering plants. Orchids and air plants burst like sun stars from limbs, trunks, and fallen logs. Twining among them all, the woody vines called lianas enhance the jungle atmosphere. Adding a final touch are the royal palms that here and there tower over the hardwood canopy—occasionally reaching 125 feet. TROPICAL HARDWOOD HAMMOCK - PINELAND
- SOUTH FLORIDA SLASH PINE
- BUSTIC
- GUMBO-LIMBO
- SOLUTION HOLE
- POND APPLE
- AIR PLANTS (ORCHIDS, BROMELIADS)
- ROYAL PALM
- LIVE OAK
- MASTIC
- VINES
- PINELAND
- SAW-PALMETTO
The limestone rock that underlies the entire park is porous and soluble; consequently the floor of the hammock is pitted with solution holes dissolved by the acid from decaying vegetation. Soil and peat accumulating in the water-filled bottom of one of these holes supports a plant community of its own: perhaps a pond apple, surrounded by ferns and mosses (including some varieties that seem to be limited to this pothole environment). A dead, decaying log on the ground may support another miniature plant community—a carpet of mosses, ferns, and other small plants that thrive in such moist situations. Strangest of the hammock plants is the strangler fig, which first gets a foothold in the rough bark of a live oak, cabbage palm, or other tree. It then sends roots down to the ground, entwining about the host tree as it grows, and eventually killing it. On the Gumbo Limbo Trail you will see a strangler fig that grew in this manner and was enmeshed by another strangler fig—which now is threatened by a third fig that already has gained a foothold in its branches. Best known of the glades hammocks is Mahogany Hammock. A boardwalk trail in this lush, junglelike tree island leads past the giant mahogany tree for which the hammock was named—now, because of Hurricane Donna, a dismembered giant. This fine tree island was explored only after the park was established. An array of large and small vertebrate animals, mostly representative of the Temperate Zone, populates these tropical hardwood jungles: raccoons and opossums, many varieties of birds, snakes and lizards, tree frogs, even bobcats and the rare Florida panther, or cougar. Not surprisingly, invertebrates—including insects and snails—abound in this luxuriant plant community. The tropical influence is evident in the presence of invertebrates such as tree snails of the genus Liguus, known outside of Florida only in Hispaniola and Cuba. Cypress Head Standing out conspicuously on the glades landscape are tall, domelike tree islands of baldcypress. Unlike hammocks, which occupy elevations, cypress heads, or domes, occupy depressions in the limestone bedrock—areas that remain as ponds or wet places during seasons when the glades dry up. Water-loving cypresses need only a thin accumulation of peat and soil to begin their growth in these depressions or in smaller solution holes in the limestone. Cypress head - BALDCYPRESS
- ALLIGATOR HOLE (often in middle of cypress head)
- SAWGRASS
Though most conifers retain their needles all year, baldcypresses shed their foliage in winter. The fallen needles decay, forming acids that dissolve the limestone further; thus these trees tend to enlarge their own ponds. Since the pond is deeper in the middle, and the accumulation of peat is greater there, the taller trees grow in the center of the head, with the smaller ones toward the edge. Hence the characteristic dome-shaped profile. Usually when fire sweeps the glades, the baldcypresses, occupying low, wet spots, are not injured. But with extended drought, the water disappears and the peat may burn for months, killing all the baldcypresses. The cypress heads sometimes serve as alligator holes, where the big reptiles and other aquatic animals are able to survive dry periods. As you drive along the park road, stop and examine these tree islands through your binoculars; they are favored haunts of many of the park’s larger wading birds. Look for herons, egrets, wood storks, and white ibis, which visit these swampy habitats to feed on the abundant aquatic life. Bald eagles find the tops of the tallest cypresses advantageous perches from which to scan the marsh. And at night certain of the cypress heads are “buzzard roosts”—resting areas for gatherings of hundreds of turkey vultures. Bayhead - ALLIGATOR FLAG
- COCOPLUM
- SWAMP HOLLY
- CABBAGE PALMETTO
- REDBAY
- SWEETBAY
- SAWGRASS
- WILLOW
- ORCHIDS AND BROMELIADS
Many of the tree islands in the fresh-water glades are of the type called bayhead. Growing in depressions in the limestone or from beds of peat built up on the bedrock, these plant communities contain a variety of trees, including swamp holly, redbay, sweetbay, wax myrtle, and cocoplum. Some of them, on the fringes of the brackish zone, are marked by clumps of graceful paurotis palms growing at their edges. Like the hardwood hammocks in the pinelands, bayheads are prevented from taking over the entire glades ecosystem by the dry-season fires that sweep the region at irregular intervals. The fires do not always affect the bayheads. A moat, formed by the dissolving action of acids from decaying plant materials on the limestone, may surround the tree island, providing some protection from fire. Wildlife concentrates in these moats during the dry season. Birds congregate here to harvest the fish, snails, and other aquatic life—and occasionally themselves fall prey to lurking alligators. Willow Head Willows pioneer new territories and create an environment that enables other plants to gain a foothold. Their windblown seeds usually root in sunny land opened by fire and agriculture. Since these trees require a great quantity of water, the solution holes in the glades are favorable sites. Seedlings grow, leaves fall, and stems and twigs die and drop—contributing to the formation of peat. When this builds up close to or above the surface of the water, it provides a habitat for other trees such as sweet bay and cocoplum; with enough of these the willow head changes character and becomes a bayhead. Years ago, when alligators were plentiful, they weeded the willow-bordered solution holes, keeping them open. Consequently, the willow heads were typically donut-shaped. Today, however, alligators are scarce and many of the willow heads have no ’gators. The solution holes fill with muck and peat; relatively tall willows rise out of the deep, peat-filled centers, with increasingly smaller ones toward the less fertile edges, and the willow heads take on the characteristic dome-shaped profile but not nearly the height of the cypress domes. They have a clumpy, brushy appearance, seeming to grow right out of the marsh without trunks. POMACEA SNAIL—The sole food of the everglade kite Willow heads with alligator holes typically have a doughnut shape—the gator hole representing the hole in the doughnut. - SPATTERDOCK
- COASTAL PLAIN WILLOW
- CATTAIL
- DRY SEASON WATER LEVEL
Willow heads that do have alligator holes have a seasonal concentration of aquatic animals and the birds and mammals that prey upon them. They rarely support orchids or bromeliads, for the bark of the southern willow is too smooth to provide anchorage for the seedlings of these plants. During drought periods willow heads, like bayheads, are vulnerable to the fires that sometimes burn over the glades. Web of Life in the Marsh Around the stems and other underwater parts of the glades plants are cylindrical masses of yellowish-green periphyton. So incredibly abundant are these masses of living material that in late summer the water appears as though clogged with mossy-looking sausages and floating pancakes. Largely algae, but containing perhaps 100 different organisms, the periphyton supports a complex web of glades life. It is the beginning of many food chains in the fresh-water marsh. The larvae of mosquitoes and other invertebrates, larval frogs (tadpoles) and salamanders, and other small, free-swimming creatures feed upon the tiny plants and minute animals living in the masses of periphyton. These periphyton feeders are in turn fed upon by small fish, frogs, and other vertebrates, which are food for big fish, birds, mammals, and reptiles; most of these larger creatures are preyed upon by the alligator. The periphyton is perhaps most important for its role in maintaining the physical environment of the marsh. The water flowing over the limestone of the glades is hard with calcium. The algae remove this calcium and convert it to marl (see glossary), which precipitates to the bottom. Sawgrass is rooted in this marl; accumulated dead sawgrass forms peat; other marsh plants, including willows and the trees of the bayheads, spring up from the peat. Acid from the peat and from decaying plant matter of the tree islands dissolves some of the marl and underlying bedrock—and the cycle is complete. Every plant, every animal, every physical element is involved in this web of life—as soil builder, predator, plant-eater, scavenger, agent of decay, or converter of energy and raw materials into food. Damage to or removal of any of these components—pollution of the water, lowering of the water table, elimination of a predator, or any interference in the energy cycle—could destroy the glades as we know them. - ALGAE AND ONE-CELLED ANIMALS
- INVERTEBRATE LARVAE
- PERIPHYTON MASS
- SAWGRASS
- SAWGRASS DIES AND MAKES PEAT
Every other plant-and-animal community in the park—hammock, mangrove swamp, pineland, etc.—is an association of large and small organisms sharing a physical environment. It is impossible to understand either the park as a whole or the life of a single creature without being aware of these interrelationships. Alligator Hole in the Glades Out in the sunny glades the broad leaves of the alligator flag mark the location of an alligator hole. This is the most incredible ecosystem of all the worlds within the world of the park; for in a sense the alligator is the keeper of the everglades. With feet and snout these reptiles clear out the vegetation and muck from the larger holes in the limestone. In the dry season, when the floor of the glades checks in the sun, these holes are oases. Then large numbers of fish, turtles, snails, and other fresh-water animals take refuge in the holes, moving right in with the alligators. Enough of these water-dependent creatures thus survive the drought to repopulate the glades when the rains return. Birds and mammals join the migration of the everglades animal kingdom to the alligator holes, feed upon the concentrated life in them—and in turn occasionally become food for their alligator hosts. Lily pads float on the surface. Around the edges arrowleaf, cattails, and other emergent plants grow. Behind them on higher muckland, much of which is created by the alligators as they pile up plant debris, stand ferns, wildflowers, and swamp trees. Algae thrive in the water. The rooted water plants might become so dense as to hinder the movement and growth of the fish, were it not for the weeding activities of the alligators. With the old reptiles keeping the pool open, the fish thrive, and alligator and guests live well. Plants piled beside the hole by the alligator decay and form soil with mud and marl. Ferns, wildflowers, and tree seedlings take root, and eventually the alligator hole may be the center of a tree island. So, it’s easy to see how important the alligator is to the ecology of the park. Unfortunately for this reptile, many people in the past believed only in the value of its hide. Hunting for alligators became profitable in the mid-1880’s and continued until the 1960’s. In 1961 Florida prohibited all hunting of alligators, but poaching continued to take its toll. Finally, the Federal Endangered Species Act of 1969 protected the alligator by eliminating all hunting and trafficking in hides. As a result of complete protection, the alligator has increased greatly in number. They are no longer an endangered species in Florida, and they can easily be found in gator holes and sloughs. Today alligators are eagerly sought by visitors to Everglades National Park who are anxious to see and photograph this unique creature. Once again, the alligator is the keeper of the everglades. ACTUAL SIZE AT HATCHING (8 to 10) Alligator - FOOD
- FISH (gar, bass, etc.)
- BIRDS
- TURTLES (soft-shelled and others)
- MAMMALS
- RACCOON
- SNAPPING TURTLE
- GREEN HERON
40 TO 60 EGGS LAID IN NEST OF HUMUS IN MAY OR JUNE MOTHER TENDS YOUNG 1 TO 2 YEARS
1 YEAR OLD: ABOUT 2' LONG ALLIGATOR HOLE IN THE GLADES - SNOWY EGRET
- WHITE IBIS
- WOOD STORK
- MOSQUITO (15 species)
- SNAIL EGGS
- PIG FROG
- ALLIGATOR NEST
- DRY SEASON WATER LEVEL
- GAMBUSIA
- KILLIFISH
- SUNFISH
- LARGEMOUTHED BASS
- FLORIDA SPOTTED GAR
- FLORIDA SOFT-SHELLED TURTLE
- 1 SPIKE RUSH
- 2 PINK GERARDIA
- 3 SPIDER LILY
- 4 CATTAIL
- 5 PICKEREL WEED
- 6 ARROWHEAD
- 7 WATER LILY
- 8 SPATTERDOCK
- 9 BLADDERWORT
- 10 ALLIGATOR FLAG
- 11 MORNINGGLORY
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