Global warming causes explosion in mangrove forest expansion

Global warming causes explosion in mangrove forest expansion

Mangrove forests creep north as cold snaps in Florida decline.

Florida, the sunshine state and weird news capital of the world, is home to many mangrove forests. It’s warm there, but even the great state of Florida isn’t immune to the occasional cold snap. Until recently, that is. Due to a lack of frosts, those mangrove forests have begun to expand north along the Atlantic coast, according to ecologists from Brown.

Using satellite imagery going back nearly 30 years, scientists have determined that in some areas, the mangrove forests have doubled in size.

“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,” said study lead author Kyle Cavanaugh, a postdoctoral researcher at Brown University and at the Smithsonian Institution. “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.”

The findings provide a new and unique illustration of the speed and scale on which alterations in climate extremes have affected crucial ecosystems.

Brown Assistant Professor James Kellner notes that more than just documenting the expansion, the research also identifies the cause. Cavanaugh and his researchers tested various hypotheses by correlating the satellite observations with reams of other data. What they found was the area’s decline in the frequency of days where temperature dips below -25 degrees Farenheit. As you may suspect, that’s the physiological temperature limit of mangrove survival.

Though the difference is subtle, a reduction in cold snaps is not exactly the same as an overall warming trend. In the analysis, the team, which also includes researchers at the University of Maryland, had to rule out increases in mean annual or winter temperatures as well as changes in precipitation and changes in nearby urban and agricultural landcover. They also ruled out sea level rise.

“The most intuitive explanation is not the explanation that actually explains this pattern,” said Kellner, who teaches in the department of ecology and evolutionary biology and is part of Brown’s Environmental Change Initiative. “The one people would most probably point to is an increase in mean temperature.”

Though mangroves are a protected species, their expansion isn’t necessarily an excuse to break out your mangrove-themed party favors and throw a mangrove expansion bash. Any time there’s a rapid change in an ecosystem, there are negative consequences.

“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.”

Still, for now: Mangroves, mangroves as far as the eye can see.

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