Florida's Ecosystems

These systems are strongly hydric and highly organic. They typically stay wet year round, having higher water levels than marsh systems, which may have annual dry periods due to the drought-like summer weather of southwest Florida. This means that the luxuriant flora cycles through growth and decomposition creating a low oxygen aquatic organic mucky substrate suitable for submerged and emergent plant life. Often, the fires frequent in southwest Florida will burn quickly around the edges of the swampy areas further reducing competitive, invasive, species. Typically a fire burns through a cypress swamp every 20-100 years.

The cypress swamps are the least ephemeral of the freshwater wetlands. They may be submerged as much as nine months out of the year. However, it should be noted that in order to reproduce, bald and pond cypress must have at least a few small periods when the soils are exposed to the sun and air.

The soils of cypress swamps are generally very acidic. While there is a great deal of organic matter present, it is not readily available. In fact the rates of decomposition due to the lack of oxygenated water means that dead materials are slow to decompose. During the few times yearly that the water levels fall enough that the peat and muck bottoms may be exposed, the rates of decomposition and re-growth actually increase even though the system is more stressed. While gross production may be at a high level, the net production remains low.

Often the nutrient cycles of a specific area can vary greatly from year to year. It is imperative to understanding these cycles that long term sedimentary observations are implemented. "Differences in organic matter accumulation result from differences in hydroperiod, fire frequency, and water source. (Larson, 1982).

The effects of evapotranspiration are less drastic in the deeper waters of the cypress swamps due to the dense overstory. Often the moisture and water are trapped between the aqueous substrate and the dense vegetation cover deep into the dry seasons when the rest of the wetlands are already drying out, and being exposed to the sunlight, which increases the nutrient cycle by oxidizing the organics in their substrates.

 The long hydroperiod in a cypress swamp determines the types of plants that can thrive in such a system. Plants need not only to be flood tolerant, but also to be able to survive in soil with a low oxygen content. Because the soil is inundated for much of the year, oxygen in the soil is gradually depleted. Plants that grow in this soil have specially adapted roots or other mechanisms to allow them to survive. For example, one hypothesis about cypress knees is that they are an adaptation which allows cypress trees to survive in low oxygen conditions when the rest of their root system is underwater.
Cypress trees, both bald cypress or pond cypress, are unusual in that they are deciduous conifers—they lose their needles in late fall and grow new needles in the spring. Once mature, cypress trees are extremely flood tolerant, which allows them to become the dominant species in this system.

Although fire is infrequent in this system, it serves to prevent hardwood species from becoming dominant. Lack of fire, in combination with a change in water fluctuations, may result in the introduction of hardwood species and eventual transformation of the cypress swamp into a different ecosystem.

A popular misconception is that water in a swamp is stagnant, when in fact it moves slowly through the swamp. Therefore, changes to the water in systems that are "upstream" from a cypress swamp will eventually affect the water and living organisms in the swamp as well. Conversely, swamps affect "downstream" ecosystems by the water that flows out of the swamp. Swamps act as filters for sediments and pollutants that enter the system, which benefits the systems into which those swamps drain. In Lee County, for example, water that enters the Six Mile Cypress Slough eventually drains into Estero Bay.

Changes to the hydrology of a cypress swamp can have strong impacts on the system. Drainage of a swamp will allow less flood-tolerant species to become established. Wastewater discharge may increase both the volume of water and the amount of pollutants entering a swamp. Pollutants tend to settle out of water traveling through a swamp, and excessive amounts of these pollutants can damage or kill the plants and animals living there.

Historically, cypress trees have been used as a source of lumber in Florida, with the result that most cypress swamps contain second-growth cypress. Removal of cypress trees changes the overall species composition of the ecosystem, and removes habitat for species such as epiphytes and cavity nesting birds. Another use of swamps by humans is as a source of peat. Removal of peat from a swamp is extremely detrimental, as it accumulates very slowly and therefore is not easily replaced.

Odum, Odum, and Brown (1998) contend that many Florida lakes "…are as shallow ponds." This is due to a somewhat unclear difference between the definition of lakes and ponds (Horne & Goldman, 1994). Some definitions focus on the presence of higher aquatic plants, while others use mixing as a defining characteristic. Miller (2000) stated "…large natural bodies of standing freshwater- formed when precipitation, runoff, or ground water seepage fills depressions in the Earth’s surface- are called lakes." Often integrated with that definition is the presence of a barren wave-swept shore denoting the body as a lake. Although lake designation is somewhat unclear, lake formation is a better known process. Over millions of years, rainwater has percolated through wetlands, dissolving underlying limestone, thereby creating water-filled depressions and sinkholes. Some lakes also formed among dunes when seas retreated (Odum et al., 1998).

The slow process of dissolution is the reason that Florida’s lakes are shallow. In fact, three-quarters of Florida’s lakes are less than five meters (m) in depth, including Lake Okeechobee, the second largest lake by surface area in the lower 48 states (Florida Conservation Foundation, 1993). Collier County in South Florida contains one of the State’s deepest lakes, Deep Lake, at 29 meters. A large surface area, coupled with year-round warm temperatures, results in high evaporation rates from Florida lakes. That which does not evaporate percolates downward into the aquifer (Myers & Ewel, 1990). Typically unstratified, shallow lakes can be highly productive (Myers & Ewel, 1990). An unstratified lake is subject to mixing by wind, distributing nutrients throughout the water column. An example of this is Lake Tohopekaliga, the waters of which are less than six inches deep, and yet contain an estimated 20 million small fishes and other animals per acre (Florida Conservation Foundation, 1993). Deeper lakes undergo thermal stratification in spring and summer months; the warm upper region is called the epilimnion, while the deeper, colder region is the hypolimnion.

Florida lakes are fed primarily from rainfall and from streams that drain the surrounding watershed; they receive nutrients from these same sources. Nutrient levels, along with the associated levels of primary production, are used to classify individual lakes as eutrophic, mesotrophic, of oligotrophic (Miller, 2000). The natural process of gradual nutrient accumulation is called eutrophication. A lake that is high in nutrients is eutrophic. In contrast, low nutrient levels are oligotrophic. Most lakes in Florida are eutrophic due in large part to farm runoff, wastewater release, and industrial discharges (Odum, et al., 1998). Runoff from adjacent ecosystems supplies lakes with both nutrients and organic matter-often in overabundance. Nutrients are optimal when in particular concentrations: the Redfield Ratio of 116 parts carbon: 16 parts nitrogen: 1 part phosphorus is often used as a measure of optimality and to identify nutrient limitation. For example, the lakes on the FGCU campus have N:P ratios of approximately 30, suggesting that phosphorous is the nutrient that most limits aquatic plant growth. 

Lakes have three groups of primary producers: phytoplankton, benthic algae, and emergent plants. These producers provide food, refuge, oxygen, and protection for zooplankton, other invertebrates, fishes, amphibians, reptiles, and wading birds (Odum et al., 1998). Emergent plants also act as sponges for incoming runoff and the nutrients it brings. Some emergent plants such as water hyacinth (Eichhornia) and hydrilla may actually alter temperatures by blocking out the sun, alter mixing by blocking the wind, and alter gas exchange by reducing surface area. A few common plants found in Floridian lakes are listed below.

Freshwater covers a mere one-percent of the Earth’s surface, however it contains 41% of known fish species (Miller, 2000). Fishes found in lakes on the Florida Gulf Coast University campus are are provded in the species list, as are reptiles, wading birds and birds of prey.

There are four pronounced zones that can be identified in lakes: the littoral zone, the limnetic zone, the profundal zone, and the benthic zone. The littoral zone is the shallow zone near shore, to a depth at which rooted plants do not grow. It is the most productive zone, high in biodiversity, sunlight, and nutrients (mainly due to runoff). Here you may find cattails, waterlillies, muskgrass, duckweed, decomposers, frogs, insects, and fish. The limnetic zone is the sunlit open water away from the shore. Phytoplankton, zooplankton, small and large fishes are present, but are usually less abundant than in the littoral. The profundal zone is deep open water that is devoid of light; as a result, photosynthesis does not occur here. The benthic region is the bottom of the lake, where infaunal and epifaunal organisms are present. Decomposers such as bacteria and fungi, along with detritus-feeding clams, worm-like insect larvae, and catfish dominate this region (Miller, 2000). The littoral and limnetic zones receive oxygen via photosynthesis. Oxygen concentrations decline at night as photosynthesis shuts down but respiration continues, or in association with increasing water temperatures. 

Pollution has a variety of impacts on ecosystems and often ends up in lakes and other water bodies. Anthropogenic inputs of nitrates and sulfates to the atmosphere ultimately form nitric and sulfuric acid and further enhance the already acidic nature of Florida’s water and soil. Acid rain is less impacting in Florida than in northern regions, because of the underlying limestone. Deforestation, mining, construction, road building, channelization of waterways, and pumping of groundwater also contribute to decreasing water quality (Myers & Ewel, 1990). The conversion of land use in surrounding wetlands and other regions of the watershed have also exposed lakes to increased pollution and sedimentation (Florida Conservation Foundation, 1993).

Freshwater lakes are diverse, complex systems that provide a wide array of benefits for ecosystems and organisms that lie near or are connected to them. As a result, lakes influence adjacent terrestrial ecosystems to the same degree that surrounding ecosystems influence lake ecology.

Florida mangroves can be distinguished from one another based upon their physical characteristics as well as their general location. Red mangroves possess prop roots-large curved roots that surround and entangle the trees. Because of the three-dimensional structure provided by the prop roots, both above and below the water, they attract entire communities of organisms, including mangrove periwinkles (Littorina angulifera) and mangrove crabs (Aratus pisonii). Coffee-bean snails (Melampus coffeus) actually migrate up and down the prop roots with the rise and fall of the tides (Kaplan, 1988). In comparison, black mangroves, possess small "erect lateral branches of an otherwise horizontal root system" (Nelson, 1994) known as pneumatophores. These look like small pencils projecting out of the adjacent sediments in all directions. White and gray mangroves are located further inland, on more elevated sites with drier soil. In general, mangroves are distributed along a transect from the marine environment to land in the following order: red, black, white, and gray.

Mangrove communities are characterized by a diversity of flora and fauna. The saltwort (Batis maritime) is a mangrove plant that is located in close proximity to very salty, shallow ponds. Sea oxeye (Borrichia frutescens), glasswort (Salicornia virginica), and southern glasswort (Salicornia perennis) are a few of the prominent species found occupying mangrove communities. Southern glasswort is a reddish-stemmed, thin, asparagus-like plant that forms dense aggregations (Kaplan, 1988). In addition, mangrove communities are often skirted with large colonies of mangrove ferns (Acrosticum aureum).

Mangrove forests contribute to an extremely complex food web. Mangrove leaves may be broken down either mechanically or biologically and are continually being colonized by bacteria, fungi, and protozoans. The resulting small particles of organic matter may then be eaten by small fish and crustaceans, which are in turn fed upon by larger fishes and invertebrates. The thick mud that accumulates around mangroves is also dominated by a variety of crabs which aid in the further breakdown of mangrove detritus. As a result, the mangrove crab Sesarma, the wharf crab Pachygrapsus, several species of fiddler crabs, the spotted mangrove or tree crab Goniopsis cruentata, the mangrove mud crab Eurytium limosum, the common mud crab Panopeus herbstii, and the mangrove land crab (Ucides cordatus) all play an important role in nutrient cycling (Kaplan, 1988).

The result is that this detrital food base helps support enormous number of birds, reptiles, mammals, fish, and invertebrates. Mangroves serve as nursery areas for many economically important species of fishes and invertebrates as well. Furthermore, many species of shore birds nest among the mangroves including brown pelicans (Pelicanus occidentalis), little blue and tricolored herons (Egretta tricolor), great (Casmerodius albus) and snowy (Egretta thula) egrets, white ibises (Eudocimus albus), and frigate birds (Campbell, 1988; Alden et al., 1998). Birds such as osprey, bald eagle, red-breasted merganser, and roseate spoonbill (Ajaia ajaja) forage near the mangroves, as do otters, mosquito fish, killifish, mangrove salt marsh snakes, snapping and soft-shelled turtles, snook, redfish, snapper, pink shrimp, and baby alligators.

Red mangroves apparently facilitate the process of succession within mangrove systems. Kaplan (1988) defines succession as, "the sequence of events by which a biotic community constantly changes in composition until it achieves near-perfect balance with its environment" (p. 173). The end point of succession is referred to as a climax community, and often takes years and even decades to reach. In mangrove communities, this end point is characterized by the colonization of white mangroves and buttonwoods.

Mangrove propagation (seed production) begins with a yellow waxy flower that transforms into a brown lima bean-shaped embryo known as a propagule. Once in water, the waxy end of the propagule causes it to float vertically, thereby allowing for the seed to be dispersed by water currents. When the propagule comes in sufficient contact with soft bottom, usually at low tide, it lodges in the substrate and begins to drop its roots. Within three years the growing prop-root system begins to alter local currents, slowing water movement and causing suspended particles to begin settling to the bottom. This accumulation of particulate matter and leaf litter slowly transforms the muddy substrate. One acre of mangrove trees drops approximately three tons of leaves per year, further altering the bottom (Kaplan, 1988; Alden et al., 1998).

The protein value of this leaf litter is continually increased as it is colonized by mold and bacteria. As the leaves are broken into smaller and smaller particles by both mechanical and biological processes, the surface area of individual particles is greatly increased. When mixed with sand, this coarse organic matter forms a rich, densely packed sediment. Algae move in and help further stabilize the mud. After extensive growth and soil accumulation, supplemented by leaf litter and detrital development, new shrubs and small trees begin to grow. Black mangrove colonization contributes additional leaf-litter, further elevating and drying the area until eventually the more elevated, drier ground encourages the influx of white mangrove and buttonwood, thereby completing the succession process.

The above flora and fauna are as important to a mangrove ecosystem as the system is to the water bodies that it fringes. Mangroves serve to catch garbage such as bottles, cans, bags, etc. before it enters rivers, bays and the ocean. They also filter agricultural and urban runoff such as fertilizers, pesticides, fecal matter, and silt. Mangroves not only protect the water from the land, but they also protect the land from the water. Hurricane Andrew was one of the most devastating storms in Florida’s history. In many areas, the first line of defense against this storm was the coastal mangrove system which provided a buffer against wave action, storm surge, and coastal erosion.

Pine flatwoods are the "high and dry" ecosystem in Southwest Florida, referring to their relatively high elevation and the fact that these systems are less likely to be inundated than other area ecosystems. Cap rock is often visible upon casual inspection and becomes conspicuous following the frequent fires common to this system. Limestone or sandstone cap rock is permeable and porous, usually resulting in xeric (dry) conditions. Due to the quick drainage properties of this cap rock it is necessary for plants to be adapted to short or virtually nonexistent hydroperiods.

As southwest Florida is an ancient sand bar, soils tend to be porous, acidic, and low in major plant nutrients. The soils are derived mainly from coastal plain sediments ranging from heavy clay to gravel, with sandy materials predominant. Silty soils occur mainly on level expanses. Sands are prevalent in hilly areas, but they also cover broad flats in central Florida.

While there may be prolonged seasonal rains, the porosity of the soils and the rapid tropical evapotranspiration process tend to prevent any type of long-term hydroperiod. Nutrient cycling is rapid and accounts for the rapid recovery of burned areas. As soon as the nutrients become available to new growth, the fire-induced reproduction begins immediately.

The flora of the upland pine systems varies a great deal from location to location and depends on many factors such as: soil type, moisture content, nutrient cycle, and temperature gradient.

Often ecotonal systems, upland pine sites offer a melding of the surrounding ecosystems as well as provide unique qualities that some species have adapted specifically for. Pine uplands provide habitat for a wide variety of animals. Except for a few isolated areas where black bear or the endangered Florida panther are found in small numbers, the whitetail deer is the only large indigenous mammal. Common small mammals include raccoons, opossums, flying squirrels, rabbits, and numerous species of ground-dwelling rodents. http://www.fs.fed.us/colorimagemap/images/232.html

"In addition to the wide variety of species common in many of the states upland habitats, a few species are more or less restricted to the high pine. There are some reptiles and amphibians which require the loose, open sand for movement and burrowing, as well as the species dependent on the burrows of the endangered gopher tortoise. There are also numerous bird species common (although not restricted) to the high pine, including: the red-cockaded woodpecker, common ground dove, eastern kingbird, eastern bluebird, pine warbler, and hairy woodpecker, among others." http://www.ficus.usf.edu/docs/fl_ecosystem/upland/up-scrub.htm

Fire is a common characteristic of pine flatwoods ecosystems, with fires historically occurring as often as every one to eight years. Plant species within pine flatwoods are generally well-adapted to fire, and the frequency of fires in this system tends to prevent other species from becoming established.

Upland pine areas are distinctly independent ecosystems. However, they may also be common ecotonal areas (transition zones) between low lying grassy or marshy ecosystems and elevated systems such as the highly xeric ridge systems and scrub areas. 

Pine flatwoods are important ecosystems, but they were historically overlooked as wastelands good only for the pines that grew on them. These systems may be evolving due to the low intensity of prescribed burns that have become standard in southwest Florida. This management system may well be ineffective due to the lack of infrequent intense burns that these areas have evolved to accommodate. 

Wet prairies Wet Prairiesare shallow basins that have good tolerance to both flooding and drying out. Wet prairies have short hydroperiods, having less than six months of inundation (standing water) resulting in the most species-rich of all Florida marshes. The soil is sandy with some organic content. Organic matter accumulation is low, only a few centimeters at most, as opposed to cypress swamps that accumulate ten times that amount, and more. Wet prairies also have high fire frequency, ranging from once every two to four years to once per decade. This limits woody vegetation invasion, which retards or sometimes reverses peat accumulation. Compared to other types of Florida marsh ecosystems, wet prairies have a shorter hydroperiod (amount of time when the land is inundated), more frequent fires, and lower accumulation of organic matter.

Although wet prairies support a greater number of amphibian and reptile species, like the green tree frog (Hyla cinerea), mud turtle (Kinosternon bauri), pygmy rattlesnake (Sistrurus miliarius), and american alligator (Alligator mississippiensis), marshes in general have a wide species variety. Dragonflies, mayflies, mosquitoes, and horseflies are all found in marshes, in addition to some large mammals like the white-tailed deer (Odocoileus virginianus) and Florida panther (Felis concolor coryi). Birds such as the green-backed heron and white ibis frequent marsh habitats. Threatened and endangered species such as snail kites (Rostrahamus sociabilis) and wood storks (Mycteria Americana) forage in marshes and nest in swamp forest vegetation. The wood storks rely on this system for their food supply, and their numbers are still decreasing partly because of wetland drainage that reduces food availability for growth and reproduction.

Wet prairie systems are often associated with hydric (wet) or mesic (wet part of the year, dry part of the year) flatwoods, dry prairie, and hammocks. Animal species from these neighboring ecosystems often make use of the wet prairies as well. When fire occurs less frequently, wax myrtle may begin to dominate the system. Wet prairies in South Florida are also prone to invasion by melaleuca. Recovery from disturbances to the system is often slow, and introduction of other species may result in permanent changes to the ecosystem.

Marshes provide numerous environmental services such as recreation, flood control, fish and wildlife production, and water storage and supply. Although valuing wetlands in general is difficult, marsh services can and have been valued. The fisheries value is $1,333 per acre per year, and the water-treatment value is $1,112 per acre per year (University of South Florida). These figures alone provide reason enough to preserve marshes, but marshes play an even greater integrated role. Not only do they filter excess pollutants from residential and agricultural runoff, but they also foster evapotranspiration. This release of water vapor that condenses into rainfall is comparable to the amount that condenses from open bodies of water. Active management needs to occur to stop the lowering of groundwater levels: 46% of Florida’s 20 million wetland acres have been destroyed, and an additional 26,000 acres per year are still being destroyed (University of South Florida).