PLANT-AND-ANIMAL COMMUNITIES (continued)

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 that would otherwise be almost impenetrable except to a snake.

TROPICAL HARDWOOD HAMMOCK. (click on image for an enlargement in a new window)

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.

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.

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.

TREE SIGNALS. There are 52 color forms of Liguus fasciatus found in south Florida.

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, in vertebrates—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.