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Florida's Mangroves Are Expanding Thanks to Climate Change

Fewer extremes in cold weather mean mangrove forests are spreading northwards.

by Mat McDermott
Jan 2 2014, 5:50pm
Mangroves on the Florida coast. Photo via Robert Neff/Flickr

The effects of climate change on Florida’s coastal ecosystems are already being felt, as new research published in the Proceedings of the National Academy of Sciences has found that mangrove forests are moving northward. That's good news in some ways, but could be bad in others.

Researchers from the Smithsonian Institute, Brown University, and the University of Maryland examined NASA satellite data from 1984 to 2011, which revealed that mangrove forest has increased by over 3000 acres along the coast from Palm Beach County, immediately north of Miami, all the way up to Saint Augustine. The largest increases occurred between Cape Canaveral National Seashore and Saint Augustine, where mangrove area doubled in the time period. 

They associated this mangrove forest expansion with a reduction in extremes of cold weather. Over the same time period, Daytona Beach, located roughly in the middle of the greatest increase in mangroves, experienced an average of 1.4 fewer days per year where temperatures fell below 28.4°F. In the southernmost areas examined, the number of below-freezing days was unchanged. 

Land use and precipitation changes, as well as changes in average winter temperatures, were eliminated as potential causes of the mangrove increase, as were overall temperature increases in the regionif they were begind it, mangroves would’ve increased across the entire area studied, not just the northern part. This decrease in the number of days with mangrove-killing low temperatures as the only remaining factor.

In one way, more mangrove forests is a positive step: around the world, they're increasingly threatened by humans, with a destruction rate four times that of other forests. Since 1980, 20 percent of the world’s mangroves have been cleared to make way for human settlement, and since the 1950s humans have cleared up to 50 percent of the mangrove forest that then existed. Roughly a quarter of the remaining mangroves are protected from development, with losses occurring at an annual rate of one to two percent.

From the perspective of climate change, mangrove forest and coastal wetland is a vital carbon sink, storing 50 times more carbon than other tropical forests by area. When it's cleared, however, it's a potent source of carbon emissions. Despite making up less than one percent of the area covered by tropical forest, mangrove clearance is responsible for 10 percent of of emissions from global deforestation

In addition to their climate benefits, mangrove forests provide many important resources for nearby human settlements. The waters around them create some of the most productive areas for fish and shellfish, and mangroves act as a barrier in the case of hurricanes, tsunamis, and sea level rise, as well as helping slow natural erosion. According to UNEP calculations, mangrove forests provide up to $22,000 per acre worth of ecosystem services and direct revenue. 

In light of the marked advantages mangrove forests bring us, their expansion on the Atlantic coast of Florida seems like an all-round good thing. However, as study lead author Kyle Cavanaugh pointed out, “This is not taking place in a vacuum. The mangroves are replacing salt marshes, which have important ecosystem functions and food webs of their own.” 

As for the long-term effects of this ecosystem shift, study co-author Professor Daniel Gruner said, “At this point we don’t have enough information to predict the consequences.” 

The report noted that climate change will threaten 10-20 percent of mangroves by the end of this century, due to sea level rise and precipitation and temperature changes. Some amount of lost mangrove forest may be offset by expansion of suitable areas, but how this expansion will compare to losses remains to be seen.