How climate change benefits Florida forests

Mangroves are on the move. In Florida, these valuable coastal forests have expanded to the north — thanks to a drop in the number of cold snaps.

Mangroves are important ecosystems that support fish, birds, and other coastal critters. They also store carbon and provide a buffer against damaging storms. Researchers estimate that these “services” are worth about $1.6 trillion per year.

But mangroves are in trouble: They’re being pushed out by fish farms and construction along the coasts. To find out if these losses might be offset by changes in climate, the study authors analyzed satellite images of Florida taken from 1984 to 2011. They also examined records from weather stations in the area.

In the northern part of their range, the area occupied by mangroves roughly doubled, the team reports in Proceedings of the National Academy of Sciences. While 464 hectares of mangroves were lost in the south, 1,700 hectares were added in the north.

The changes weren’t linked to a rise in average temperature, the authors say. Rather, a drop in the number of cold snaps — or days when the temperature dips below −4 degrees Celsius — likely triggered the expansion. With more warming, mangroves could march poleward in other parts of the world too.

More forests is good news, right? Not necessarily. “Some people may say this is a good thing because of the tremendous threats that mangroves face,” said co-author Kyle Cavanaugh of the Smithsonian Environmental Research Center in Edgewater, Maryland in a press 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.” Scientists will have to wait and see whether the mangrove takeover does more harm than good. Roberta Kwok | 31 December 2013

Source: Cavanaugh, K.C. et al. 2013. Poleward expansion of mangroves is a threshold response to decreased frequency of extreme cold events. Proceedings of the National Academy of Sciences doi: 10.1073/pnas.1315800111.

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