The Everglades of the southern portion of the Florida Peninsula is a spatially and temporally heterogeneous region of plant communities which derive their diversity from climatic factors and periodic severe weather events. Florida is an extremely flat land underlain by limestone deposits, characterized by shallow soils, affected by a 12,000 year history of steady sea level rise. The Everglades ecosystem—the most intact portion of which is found in Everglades National Park—is based on sheet flow of an extremely shallow, wide, slow moving body of water. Water flows through the Everglades from Lake Okeechobee and the Kissimmii River System to the north. It empties out in Florida Bay, which is itself a highly important ecosystem. The water moves at a rate of a few feet a day in a river which is up 65 miles wide and no more than 6 to 12” deep. The extremely slow sheet flow is due to a tilted substrate which dips no more than one foot for every ten miles to the south.
Limestone bedrock underlies the Everglades, limestone having been deposited in earlier geologic times when South Florida was below sea level. The present plant associations of the Everglades—mangroves, coastal prairies, tree islands, and sawgrass marshes are approximately 5000 years old, according to geologic and pollen studies. Florida’s climate has both temperate and subtropical features. The Everglades are on the southern edge of the North American temperate region where broad-leaved temperate species of plants are found, as well as the subtropical zone of the Caribbean and the West Indies. The plants and animals of the Everglades combine continental and West Indian origins.
South Florida has a summer wet season and a mid fall to late spring dry season. Greatest levels of precipitation are in the period June through September, with winter dry season or drought occurring during November through May. Coastal flooding occurs with summer and fall hurricanes. In times of drought, fires play an important role in Everglades ecology in sawgrass marshes, pinelands, and hardwood hammocks.
The annual hydro-period of the Everglades is critical to the distributions, feeding behaviors, and reproductive success of a number of species of vertebrates, including the American Alligator, American Crocodile, Snail Kite (a beautiful hawk with highly specialized diet), Wood Stork, numerous other colonial wading birds, River Otter, White-tailed Deer, and Florida Panther. Rainfall patterns appear to be associated with 5 to 8 year global climate cycles, including the El Nino-South Oscillation (ENSO) events originating in the Pacific Basin—which I will not describe here.
Average temperatures in the Everglades are warm year-round, including summer and winter daily maximums and minimums. Because occasional freezes occur in winter, minimum temperatures have the greatest effect on the geographic distribution of Everglades plants and animals. Most water enters the Everglades system through thunderstorms (either here or further north). Most water leaves the system through evapotranspiration, which is greatest in the late spring and summer growing season. Precipitation results from warm maritime air coming in from the Caribbean and cold continental air from further north.
The hurricane season is from June through October. Every year since the mid 1800s has had at least one hurricane strike the Florida peninsula; often there are several hurricanes in a season. Some of them have severe effects on Everglades ecology, particularly the (coastal) forested areas of the mangroves, pinelands and hardwood hammocks (see slides for descriptions of these plant communities). The most common severe weather events in the Everglades, then, are floods, droughts, freezes, hurricanes or tropical cyclones, and fire. I develop further connections between Everglades ecology and climate in the Sample Lesson Plans section of the unit and through available classroom materials.