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Pollen records from all three transects indicate wetter than modern conditions before 1000 yr BP. These results are consistent with other sediment cores collected in the historic ridge and slough landscape (Willard and others, 2001b). Before 1000 yr BP, the ridge assemblages were analogous to a prairie and marsh-like environment with moderate hydroperiods and water depths. The transition zone and slough sites were analogous to modern sloughs before 1000 yr BP. This indicates that the ridges were narrower with sparser sawgrass vegetation before 1000 BP, with broader Nymphaea-dominated sloughs.
Beginning about 1000 yr BP, vegetation characteristic of drier conditions is more common in assemblages from all sites. In ridge assemblages, the greater abundance of fern spores and Cladium, Asteraceae, and Chenopodiaceae-Amaranthaceae pollen are analogous to sawgrass marshes, indicating shallower water and shorter hydroperiods. In the transition zone, Nymphaea pollen abundance decreases and pollen of Myrica, Apiaceae, and Asteraceae and fern spores became more abundant. This indicates a shift from a slough to a drier transition zone. Slough pollen assemblages contain greater percentages of fern spores and Myrica, Cephalanthus, Asteraceae, and Chenopodiaceae-Amaranthaceae. However, the center of the sloughs were analogous to modern sloughs throughout the interval from ~1000 yr BP to 1900 AD. The expansion of ridges at the expense of adjacent sloughs is consistent with a shift toward shorter hydroperiods and shallower water and may reflect wetland vegetation response to drier conditions associated with the Medieval Warm Period climate anomaly (Willard and others 2001b).
The impact of 20th century and anthropogenic changes on the ridge and slough landscape is notable. Increased abundances of Cladium, shrub, and weedy pollen and fern spores indicate substantial drying of the ridges during the early 20th century. These species became more abundant within the transition zone. Although species characteristic of drier conditions increased in abundance slightly in sloughs during the 20th century, pollen assemblages still are analogous to the slough vegetation that persisted throughout the 20th century. Ridge and slough assemblages were virtually unchanged between 1950 and 2002, indicating that the latest rapid vegetation responses were synchronous with the compartmentalization of the Everglades ecosystem.
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 04 September, 2013 @ 02:03 PM (KP)
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