publications > paper > PP 1011 > ecosystems > freshwater and terrestrial > pine forests
Ecosystems of south Florida
Freshwater and terrestrial ecosystems
Pine forests occur on rock outcrops and sandy flatlands that are
seldom flooded for more than a few weeks each year. They once occupied about 5,180 km2 (2,000 mi2) but have been reduced by about half (Birnhak and Crowder, 1974). The major areas of pine forests are in the Big Cypress Swamp, on the Atlantic Coastal Ridge, and on the sandy flatlands north of the Big Cypress Swamp and northeast of the Everglades. In much of the Big Cypress Swamp the pine forests grow on small islands of limestone several inches to several feet higher than surrounding cypress forest land. In the northern Big Cypress Swamp, however, and in the flatlands to the north and northeast, these forests occur extensively on a relatively high sandy soil. Interspersed with the pines are prairies and depressions or low areas of marsh and swamp. In the western Big Cypress Swamp, pines and cypress grow together over large areas of poorly drained soil. On the Atlantic Coastal Ridge, generally 3 to 7.5 m (10 to 25 ft) above sea level, pines grow on extremely rough and solution-pitted oolitic limestone. Interspersed within the pine forest are numerous hardwood hammocks and small areas of swamp associated with the solution holes. Low transverse valleys or glades containing vegetation similar to that in the Everglades dissect the ridge to break the continuity of the pine forest. Organic soils are thin or absent in the pines of the Atlantic Coastal Ridge bur thicken in the hammocks, solution holes, and the transverse glades. The pines on the ridge once formed a more or less continuous band from Miami southwestward into Everglades National Park (fig. 12). Most of this forest outside the park, however, has been destroyed.
Characteristic plants of the pine forests are the slash pine and a variety of hardwood trees and shrubs, palms, grasses, and other plants. Cabbage palms and saw palmetto are widely distributed throughout. Grasses are often the dominant ground cover; common genera include beardgrass, wiregrass, and panicgrass. The distribution of pine-forest plants is influenced by temperature and soil conditions, among other factors. Along the coastal ridge, generally south of Miami, pine forests are characterized by an understory of tropical trees and shrubs such as poisonwood, myrsine, tetrazygia, marlberry, bustic, varnishleaf, satinleaf, silver palm, and the cycad, coontie. To the north and west tropical species are replaced by cold-tolerant species. On the pine islands of the Big Cypress Swamp, where soils are neutral or alkaline, cabbage palm, wax myrtle, gallberry, and a variety of grasses and sedges are typical understory plants. In the northern Big Cypress Swamp and in the sandy flatlands where soils are acidic, cabbage palms decline, and saw palmetto often dominates as the understory shrub, particularly on the drier lands. Other common plants characteristic of the acid, sandy soil of the flatlands are staggerbush. rusty lyonia, shiny blueberry, and running oak (Davis, 1943).
Fire is important in the pine-forest system. Without fire, hardwood trees flourish, and in about 25 years hardwood hammock forests replace the pine forest (Alexander and Crook, 1973). Fire checks this succession by reducing the spread and density of the hardwood trees. Fires caused by lightening are common in the wet season, but in general fires during this season are not severe; because of moisture they are not extremely hot, and they do not burn deep into the rock and soil. Such fires prune the hardwood trees and shrubs and do little damage to the fire-adapted species. Man-caused fires, on the other hand, often occur in the dry season and can be destructive if water levels are low enough to allow the fire to burn into the soil and to burn at a high temperature. In such cases the fire-adapted pines may be killed if their roots are burned. Man-caused fires are now the most common type (Hofstetter, 1973).
|Fire may have either beneficial or detrimental effects on south Florida's ecosystem. [larger image]
Not all man-caused fires occur in the dry season. Some are started during high-water periods to maintain the pine forest. Burning during high water reduces the competing hardwoods and the amount of dry, burnable litter that might cause a severe fire during the dry season. Much of the pine forest of Everglades National Park is burned intentionally (control burning each year during high water for this reason.
Animals of the pine forests include numerous arthropods and other invertebrates, a variety of amphibians, reptiles, birds, and mammals. Representatives of 202 families of arthropods, including 84 insect families, were recently collected in the pine forests on the Atlantic Coastal Ridge (Hofstetter, 1973). Spiders arc often conspicuous in the pines; major families in Everglades National Park are the jumping spiders, crab spiders, cobweb weavers, and the orb weavers (Hofstetter, 1973). Amphibians and reptiles, including frogs, toads, lizards, snakes, and turtles, are represented by about 13 species (Crowder, 1974b). Species, such as the indigo snake and the Florida pine snake have declined in population (Crowder, 1974b). A large variety of birds reside in or migrate through pine forests; bobwhite quail, turkey, and mourning doves are representative game birds. Some bird such as the southern red-cockaded woodpecker and the southern bald eagle, associated with pine forests as well as other habitats, are now endangered species (Rodgers and Crowder, 1974). Common mammals include mice, squirrels, opossums, armadillos, raccoons, and deer. Panther, once widely distributed, are now endangered (Rodgers and Crowder, 1974).
Pine forests are the most threatened of the major natural systems (Hofstetter, 1973), as a result of land clearing for agricultural or urban development. The remaining pine forests, mainly in Everglades National Park have also suffered change during the last 30 years. Hammock species, particularly poisonwood, have invaded pine lands during the years of fire protection before control burning (Alexander and Crook, 1973).
In the Eastern Flatlands, pine forests were logged in the 192O's. Regrowth has occurred, and pines, along with young wax myrtle, have spread into the margins of some ponds. This spread is attributed to decreased flooding (Alexander and Crook, 1973). In the Western Flatlands, pine forests have been logged since 1925. More recently these forests have been cleared for urban usage, farming, and citrus groves, and fires have caused total destruction of pines in some locales. The greatest threat to the remaining pine-forest system is rampant invasion by cajeput.
Cajeput is also invading the Eastern Flatlands. Cajeput now grows in cypress, pine, and old farmland where it has, in many places, formed domes resembling cypress domes. All age classes are present, so continued spreading is indicated. Brazilian pepper and Australian pine are also common invaders (Alexander and Crook, 1973).
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