Over the last few decades, mangrove forests have been expanding northward along Florida's Atlantic coast as cold snaps in the state, in the southeastern part of the U.S., have decreased significantly in frequency, a new study reveals, raising concerns about the speed and scale at which climate change has affected crucial ecosystems.
According to the findings, published in the Dec. 30 issue of the Proceedings of the National Academy of Sciences, the size of mangrove forests in places like Palm Coast in Flagler County have doubled in the last three decades. The researchers arrived at their conclusion by analyzing satellite imagery and by measuring the coastal area that is currently occupied by mangroves.
“Before this work there had been some scattered anecdotal accounts and observations of mangroves appearing in areas where people had not seen them, but they were very local,” Kyle Cavanaugh, a postdoctoral researcher at Brown University in Providence, R.I., and the study’s lead author, said in a statement. “One unique aspect of this work is that we were able to use this incredible time series of large scale satellite imagery to show that this expansion is a regional phenomenon. It's a very large scale change.”
Cavanaugh and his team of researchers tested various hypotheses by correlating the satellite observations with reams of other data. What emerged from their tests was a decline in the frequency of days where the temperature dipped below minus 4 degrees Celsius, or 25 degrees Fahrenheit, which is the limit for mangroves to survive.
In their analysis, the researchers ruled out increases in mean temperatures -- the average of the maximum and minimum temperatures -- as well as changes in rainfall and nearby urban and agricultural land-cover, and sea-level rise as a possible explanation for the activity.
“Instead seemingly subtle differences from 1984 through 2011 of just 1.4 fewer days a year below 25 degrees in Daytona Beach or 1.2 days a year in Titusville appear to explain as much as a doubling of mangrove habitat in those areas,” the researchers said in the statement.
According to the researchers, the northward expansion of mangroves is a consequence of climate change, and is not good for other species.
“The expansion isn't happening in a vacuum,” Cavanaugh said. “The mangroves are expanding into and invading salt marsh, which also provides an important habitat for a variety of species.”