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Atlas of Pollen and Spores of The Florida Everglades
Quantitative analysis of pollen assemblages from Holocene sediments provides the primary basis for interpretation of plant community response to climatic and anthropogenic environmental change (Kneller and Peteet, 1999; Watts, 1979; Davis, 1969; Willard et al., 2001a, 2003). Such analyses rely on accurate identification of fossil pollen for quantitative comparison with modern assemblages. Although a number of atlases illustrating pollen and spore morphology for taxa from the eastern and southeastern United States have been published (Jones et al., 1995; McAndrews et al., 1973; Richard, 1970 a, b, c; Lieux, 1980a, b, 1982, 1983; Lieux and Godfrey, 1982; Bassett et al., 1978), they focus primarily on tree and shrub taxa from upland sites. Recent restoration efforts in the greater Everglades ecosystem of south Florida has led to extensive paleoecological research in the vast wetland, and an extensive pollen reference collection has been assembled to facilitate identification of pollen from Everglades sediment cores. Taxa in the collection include a variety of trees, shrubs, herbs, floating aquatics, and ferns. This atlas, compiled from that collection, consists primarily of plants native to the Everglades, but some introduced species (notably Casuarina equisetifolia, Melaleuca quinquenervia, and Schinus terebinthifolius) occur commonly enough in the wetland to merit inclusion.
As defined here, the greater Everglades ecosystem extends from Lake Okeechobee in the north through the mangroves bordering Florida Bay in the south and from the developed region along the east coast of the peninsula through Big Cypress and mangrove forests in the west and southwest coast (Text-Fig. 1). The historic Everglades originally covered an area of approximately 12,000 km2 (Davis et al., 1994), but rapid population growth, agricultural development, and associated changes in water management of the system during the 20th century have reduced wetland area by about half and altered the distribution of plant communities within the Everglades. About 850 plant species grow within the greater Everglades, aggregating into fewer than 20 plant communities, including sloughs, sawgrass marshes, cattail marshes, wet prairies, tree islands, cypress domes, mangrove forests, and salt marshes (Davis, 1943; Loveless, 1959; Gunderson, 1994; Kushlan, 1990). The distribution of plant species in the Everglades is controlled primarily by hydroperiod (annual duration of inundation), water depth, and substrate type (Table 1). In the natural Everglades system, water levels fluctuated seasonally with rainfall. Changes in water-management practices during the 20th century have greatly altered the original seasonal flow pattern through the Everglades and fragmented the system through construction of canals, levees, and water-control structures. In an effort to increase water supplies to restore the Everglades to a more natural state while still meeting other regional water needs, the United States Congress authorized the Comprehensive Everglades Restoration Plan (CERP) in 2000. Research is underway to ensure that restoration targets reflect the natural pre-drainage hydrology and ecology. This research includes paleoecological studies using the pollen record from sediment cores to document the distribution of predrainage wetland plant communities and their response to specific hydrological and environmental changes.
|Text-Figure 1. Pre-drainage distribution of vegetation types in the greater Everglades ecosystem (modified from McVoy et al., 2004). Inset map shows geographic boundaries of Everglades National Park, Big Cypress National Preserve, and the Water Conservation Areas. Shaded area in inset indicates the present extent of the Everglades wetland. [larger image]
Analysis of pollen assemblages from surface samples of sediment collected in different Everglades plant communities has shown that at least eleven types can be distinguished using pollen abundance (Willard et al., 2001b). This is possible because each community has a distinctive species composition (Table 2) and because pollen of most of these species is not transported far from its source. Through statistical comparison of surface and downcore assemblages, analogs for past plant communities are identified, and vegetational responses to environmental changes are reconstructed. These analyses rely on accurate identification of pollen, and the reference pollen collection that includes the most common wetland plants has been an important tool for Everglades paleoecological research.
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