Florida Mangroves and Salt Marshes Reveal New Climate Change

What are good indicators of climate change? Mangroves along Florida's Atlantic coast are fulfilling that role. As the frequency of hard frosts has declined, these trees have expanded dramatically, revealing how environmental conditions can drastically impact the environment.

Between 1984 and 2011, the Florida Atlantic coast from the Miami area northward gained more than 3,000 acres of mangroves. All of this increase occurred north of Palm Beach County. Between Cape Canaveral National Seashore and Saint Augustine, mangroves actually doubled. At the same time, between the study's first five years and its last five years, Daytona Beach recorded 1.4 fewer days per year when temperatures fell below 28.4 degrees Fahrenheit. Yet the number of killing frosts in southern Florida was unchanged.

"Some people say this is a good thing, because of the tremendous threats that mangroves face," said Kyle Cavanaugh, one of the researchers, in a news release. "But 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."

Mangrove forests grow in calm, shallow coastal waters throughout the tropics. Salt marshes fill this particular niche in temperate zones--areas where it's too cold for mangroves. Both provide crucial habitat for wildlife, including endangered species and commercially valuable fish and shellfish. In fact, some animals use both types of habitat. They also both buffer floods, store atmospheric carbon and building soils, which prevent coastal erosion.

The fact that mangrove forests are now expanding into salt marsh territory means that salt marshes may soon be edged out of their former range. Mean winter temperatures have risen at seven of eight coastal weather stations in the study area. In addition, the mangrove expansion into salt marsh habitat has not only occurred on Florida's Atlantic coast. It's also occurred on Florida's Gulf coast.

Currently, the researchers aren't sure what the long term impacts of this expansion might be. However, they're studying the effects on coastal insects and birds in order to find out whether the change will affect coastal ecosystems. The findings could help researchers better prepare for future shifts in these ecosystems as the climate changes.

The findings are published in the journal Proceedings of the National Academy of Sciences.