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South Florida as a regional system of man and nature

Ecosystem models as an approach to resource management

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Preface
Synopsis
History of the Study
Regional System
- Early Ecosystem
- Changing System
> Ecosystem Models
Ecosystems
Hydrologic Systems
Final Word
References
Appendices
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Man and nature interact to form a system of interdependent and interconnected parts. The study of this system is called systems ecology. Unlike some other branches of science that describe change as an effect caused by one part acting upon another part, systems ecology describes changes as the interaction of parts. Models are useful to visualize and analyze such systems (Appendix I).

Systems ecology and ecological modeling concepts were used in the south Florida study to evaluate environmental problems (Lugo and others, 1971, 1973; Bayley and Odum, 1971; and Carter and others, 1973). Most of the ecological models presented in this report are qualitative. However, in phase 2 of the study, being done by the University of Florida's Center for Wetlands, quantitative data are used in the models to predict changes in the systems under different management alternatives.

South Florida is a large and complex mixture of subsystems influenced to varying degrees by man. The subsystems interconnect by energy pathways and form a regional ecosystem as shown in figure 4. The energy sources that drive the system include sun, rain, wind, waves, tides, freshwater, nutrients, fossil fuel, food, manufactured goods, people, and capital. The energy-fixing components (organic producers) include the plant biomass in the Big Cypress Swamp, the Everglades, the mangroves, the estuaries, reefs, and bays and on the agricultural land. Consumers, which convert this biomass into food and which also transform natural energy into power or capital, include wildlife, tourists, residents, machines, buildings, and others. The energy-fixing systems are linked to and provide the basic support for the urban system. The urban and the agricultural systems, however, are highly subsidized by and dependent on fossil fuels and fossil-fuel products.

illustration showing flow of energy in the south Florida regional ecosystem
FIGURE 4. Flow of energy in the south Florida regional ecosystem. [larger image]
Although the conceptual diagram shown in figure 4 is informative and led to the preceding generalizations, actual resource planning requires information obtained from more detailed. specific site studies to be effective. The systems ecology approach for resource planning has been applied in DeSoto, Charlotte, and Lee Counties during a pilot study by the Florida Coastal Coordinating Council and the University of Florida (Wetterqvist and others, 1972). In that study, subsystems were classified and energy flows diagrammed to produce a model from which tentative suggestions were made for planning in the southwest Florida coastal zone. Another example is a study of the urban systems of Lee County (Brown and Genova, 1974) in which detailed recommendations were made.

A model of the regional ecosystem, such as that shown in figure 4, provides an overview and can help in identifying deficiencies in the information needed for formulating specific land-use recommendations, but it lacks the detail and quantification needed for resource planning and decisions. By breaking down the regional ecosystem into subsystems, more detail is provided. In this report the regional ecosystem is divided as follows:

Freshwater and terrestrial ecosystems:

Canals and lakes
Ponds and sloughs
Sawgrass marshes
Wet prairies
Pine forests
Cypress forests
Mixed swamp forests
Bay heads
Hardwood hammocks
Palmetto and dry prairies

Coastal ecosystems:

Sandy beaches
Mangrove and salt marshes
Shallow estuaries and bays
The reef tract

Man-dominated ecosystems:

Agricultural
Urban

Because of the special importance of water in south Florida, a separate section of this report devoted to hydrologic systems discusses problems concerning water quantity and quality.

To be most useful in resource management, systems models should be quantitative; they not only should show relationships between energy sources, storages, producers, and consumers but should show the magnitude of these relationships as well. For example, computer simulation of a sawgrass marsh model indicated that high inputs of phosphorus would result in increased transpiration and fires in the marsh (Bayley and Odum, 1971). As part of the south Florida study, quantitative data on the regional ecosystem are being amassed by a team at the University of Florida's Center for Wetlands. With these data and with the models developed in this study, computer simulation will be used to predict the effects of various management alternatives on the south Florida ecosystem.

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