Florida Keys News - Islamorada/KL Free Press
Wednesday, November 13, 2013
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Higher seas changing habitat

SOUTH FLORIDA -- Coastal areas of the Everglades region, including portions of Key Largo, experienced significant reductions in plant life last decade as a result of saltwater inundation, according to a peer-reviewed paper published last month in the scientific journal Wetlands.

Though the extensive South Florida canal network built in the middle of the 20th century has reduced freshwater flow into the southern Everglades, the most important contributor to the saltwater intrusion is sea level rise, explained paper author Douglas Fuller, a University of Miami geography professor.

"In the past decade, nothing much has changed with the plumbing," Fuller said in reference to the canal system. "So it's probably more the sea level rise."

By analyzing satellite imagery for the years 2001 through 2010, Fuller concluded that plant life has diminished in 84 percent of the areas where statistically significant changes were observed. The study centered on areas around Taylor Slough, which is the largest natural freshwater source for Florida Bay. But it also included much of Key Largo as well the northern coast of Florida Bay and the southwest coast of Biscayne Bay.

Most of the areas of decline lie close to the coast, while areas where total plant life, or biomass, increased, were mainly several miles inland. A variety of habitats that are found within about 3 miles of the Everglades coast experienced diminished abundance, including sawgrass and its cousin spikerush, as well as tree islands.

Meanwhile, the white zone, which is the area in which salt residue is visible to satellites, has expanded inland.

Even mangrove forests, which are relatively salt-tolerant and have pushed inland as sea level has risen 9 inches in South Florida over the past century, are losing density, Fuller found. Mangrove density declined in four times as many areas as it increased.

The only winners identified in the study are low-lying and highly salt-tolerant scrub grasses.

The inward march of the sea in the low-lying Everglades coastline doesn't mean the River of Grass will change dramatically in the immediate term.

"But maybe in 100 years it will be very different," Fuller said.

Still, climate scientists predict the changes will be faster in the coming decades than they have been recently. The four-county Southeast Regional Climate Change Compact, which includes the Florida Keys, Miami, Fort Lauderdale and Palm Beach, project that sea levels will rise an additional 9 to 23 inches by 2060.

To date, mangrove communities have been able to take over freshwater habitats as sea level has increased, explained Leonard Pearlstine, a landscape ecologist for Everglades National Park. In so doing, they have continued to serve as a protective barrier against storm surges. But if the rate of sea level rise, now approximately 2.5 millimeters per year, goes much higher, that could change.

"You get much above 3 millimeters per year, mangroves simply can't keep up," Pearlstine said.

Chris Bergh, director of The Nature Conservancy's Keys office, said, so far, data shows that mangroves and buttonwoods on the islands have advanced with rising seas, replacing more freshwater-dependent hardwood hammocks and pine forests.

But even that's a problem, he explained. For example, the marsh rabbit used to be abundant in the Florida Keys. But it was placed on the endangered species list in 1990. In a 2012 study, researchers determined that 48 percent of the marsh rabbit's habitat was lost to sea level rise between 1959 and 2006.

"When you have a mix of vegetation types, that's the optimum situation from the standpoint of diversity," Bergh said. "Nature tourists are attracted to diversity. These different natural communities are attached to our economy in a number of ways."

rsilk@keysnews.com

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