Mangroves, or shrub-like trees with above-ground roots snarled together that thrive in tropical conditions, have expanded along Florida's coast not because the area's average temperature has increased, but because of fewer extremely cold days, the New York Times reported. In fact, scientists attribute mangrove forests that have doubled their coverage over the last 28 years to less than 1.5 fewer cold snaps per year (cold snap = below 25 degrees) in certain areas, according to the press release.
"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 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."
Based on satellite data from as far back as 28 years, Cavanaugh and fellow researchers ruled out other climate change factors, such as rising sea levels, changing average temperatures, changes in landscape, changes in precipitation, and more. They had to avoid the obvious logic: since mangroves require tropical conditions to grow, their expansion should be due to warmer average temperatures.
"The most intuitive explanation is not the explanation that actually explains this pattern," said Brown Assistant Professor and study co-author James Kellner. "The one people would most probably point to is an increase in mean temperature."
Any species that spreads beyond its natural borders is a threat to its new environment and subsequent food chain. Mangroves crowd out marsh, where a variety of species live. (Whether those same species could thrive in the mangroves is the next question not answered by the press release.)
"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."
