The Keys are in the subtropics between 24 and 25 degrees north latitude. The climate and environment are closer to that of the Caribbean than the rest of Florida, though unlike the Caribbean's volcanic islands, the Keys were built by plants and animals.
The Upper Keys islands are remnants of large coral reefs, which became fossilized and exposed as sea level declined. The Lower Keys are composed of sandy-type accumulations of limestone grains produced by plants and marine organisms.
The natural habitats of the Keys are upland forests, inland wetlands and shoreline zones. Soil ranges from sand to marl to rich, decomposed leaf litter. In some places, "caprock" (the eroded surface of coral formations) covers the ground. Rain falling through leaf debris becomes acidic and dissolves holes in the limestone, where soil accumulates and tree roots find purchase.
The climate is tropical (Koppen climate classification Aw)[6], and the Keys are the only frost-free place in Florida. There are two main "seasons": hot, wet, and humid from about June through October, and somewhat drier and cooler weather from November through May. Many plants grow slowly or go dormant in the dry season. Some native trees are deciduous, and drop their leaves in the winter or with spring winds.
The Keys have distinctive plant and animals species, some found nowhere else in America, as the Keys define the northern extent of their ranges. The climate also allows many imported plants to thrive. Nearly any houseplant known to commerce, and most landscape plants of the South, can thrive in the Keys climate. Some exotic species which arrived as landscape plants now invade and threaten natural areas.
Some plants that seem to define the Keys are not native, including coconut palm, bougainvillea, hibiscus, and papaya.
The well-known and very sour Key lime (or Mexican lime) is a naturalized species, apparently introduced from the Yucatán Peninsula of Mexico, where it had previously been introduced from Malaysia by explorers from Spain. The tree grows vigorously and has thorns, and produces golf-ball-size yellow fruit which is particularly acidic (even in highly alkaline coral sand soil) and uniquely fragrant. Naturally, Key lime pie was invented here as well.
The Keys are also home to unique animal species, including the Key deer, protected by the National Key Deer Refuge, and the American crocodile. About 70 miles (110 km) west of Key West is Dry Tortugas National Park, one of the most isolated and therefore well-preserved in the world. The name derives from the fact that when Spanish explorers arrived no fresh water could be found, and the small hump-shaped islands look like tortoise (tortuga in Spanish) shells from a distance.
The waters surrounding the Keys are part of a protected area known as the Florida Keys National Marine Sanctuary.
Tropical cyclones
The Keys are regularly threatened by tropical storms and hurricanes, leading to evacuations to the mainland. Untouched for many years, a carefree attitude led many residents to view "mandatory" evacuations as "voluntary" and "voluntary" evacuation orders as nothing at all. The attitude proved dangerous when Hurricane Georges, after tearing up much of the Caribbean, caused damage and extensive flooding in the Lower Keys in 1998, before making landfall in Mississippi. In 2005, Hurricanes Katrina, Rita and Wilma affected the Keys (although none made a direct hit), causing widespread damage and flooding. The most severe hurricane to hit the area was the Labor Day Hurricane of 1935, a Category 5 hurricane.
Tropical cyclones present special dangers and challenges to the entire Keys. Because no area of the islands is more than 20 feet (6.1 m) above sea level (and many are only a few feet elevation), and water surrounds the islands, nearly every neighborhood is subject to devastating flooding as well as hurricane winds. In response, many homes in the Keys are built on concrete stilts with the first floor being not legally habitable and enclosed by breakaway walls that are not strongly attached to the rest of the house. Nonetheless, Monroe county, as reported in the Federal Register, has estimated that there are between 8,000 and 12,000 illegal enclosures inhabited by people.
Because of the threat from storm surge, evacuations are routinely ordered when the National Weather Service issues a hurricane watch or warning, and are sometimes ordered for a tropical storm warning. Evacuation of the Keys depends on causeways and the two-lane highway to the mainland. Time estimates for evacuating the entire Keys range from 12 to 24 hours. Evacuation estimates are significant in emergency planning, of course, but also because they are a factor in local and state regulations for controlling development. The building permit allocation was increased in 2005 when local governments reduced estimates for evacuation.
In the active hurricane seasons of 2004 and 2005, the Keys were under mandatory evacuation orders several times. In August 2004, Hurricane Charley passed about 70 miles (110 km) west of Key West, bringing tropical storm winds to the lower keys. The lower keys were evacuated in preparation for Hurricane Ivan in September, 2004 and Hurricane Dennis in July 2005, but neither hurricane came close enough to the Keys to do much damage. Hurricane Katrina, which went on to devastate parts of Louisiana and Mississippi, moved through south Florida in August 2005 and tracked southwest past Key West, causing minor damage and flooding. Hurricane Rita, which went on to destroy parts of Louisiana and Texas, grew from a tropical storm to a Category 2 hurricane as it moved westward from the Bahamas, passing south of Key West and causing damage and surge flooding as far north as Key Largo. In October 2005, Hurricane Wilma became the most devastating hurricane to hit the Keys in decades when it passed just northwest of Key West. The low-lying parts of the city were left under 3 to 6 feet (1 to 2 metres) of water from the storm surge, and major flooding was reported throughout the Keys up to Key Largo.
Courtesy of Wikipedia
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