Mangroves Pushed Further North By Climate Change: Without Frozen Winter Nights, Formerly Threatened Forests Flourish

By Ajit Jha on December 31, 2013 8:53 AM EST

Aerial view of mangroves on the Atlantic coast
Mangrove forests on the Atlantic coast of Florida are expanding northward as global temperatures warm. (Photo: Shutterstock)

A new study based on 28 years of satellite data shows how global warming impacts not just weather and climate, but also shifts the pattern forest cover. The study, based out of the University of Maryland and the Smithsonian Environmental Research Center in Edgewater, Maryland highlights how with a declining frequency of killing frosts, mangrove forests have expanded dramatically along Florida's Atlantic coast. The study was published in the journal Proceedings of the National Academy of Sciences.

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The satellite images tracked a 50-mile stretch of mangrove cover along the central Florida coast - and the researchers were surprised to see mangroves as far north as St. Augustine, Florida. The mangrove forest cover had nearly doubled between 1984 and 2011. A few decades ago, mangrove growth was kept in check by  harsh winters (at least, by Florida standards). However, with the climate changing, winter has essentially disappeared, and as a result, salt marsh grasses more tolerant towards freezing temperatures have been displaced by prospering mangrove forests.

"This is what we would expect to see happening with climate change, one ecosystem replacing another," said Dr. Daniel S. Gruner, co-author of the study and entomologist at the University of Maryland, in a press release. Gruner added that he and his fellow researchers do not have the data needed to predict the long term consequences of the ecosystem change.

The expansion of mangrove cover is comparable to the pine beetles that recently ravaged acres of pine trees in different parts of America and Canada. The common feature of both mangrove and beetle is that the disappearance of bitter cold winter nights has led to their unchecked growth.

The recent mangrove study clearly shows how rising temperatures can lead to extreme weather that impact the plant communities, according to the study authors. In addition, this study, unlike other similar studies with their focus on changes in average temperature, shows the role of changes in the frequency of rare, severe events in transforming the landscape.  

Mangroves are actually a threatened family of trees; one in six mangrove species worldwide are "in danger of extinction due to coastal development and other factors," according to the International Union for Conservation of Nature. So in that context, this finding could be a good sign. However, the study's lead author, Dr. Kyle Cavanaugh, a Smithsonian postdoctoral research fellow, holds that salt marshes "have important ecosystem functions and food webs of their own." It would be a mistake to claim one more important than the other as both forests provide crucial habitat for wildlife, including some endangered species and commercially valuable fish and shellfish. In addition, there are some animals that use both types of habitat.

Cavanaugh and his team are now turning to decades of satellite imagery of Mexico, Peru, Brazil, Australia, and New Zealand, in order to determine if mangrove forests are expanding there in the same patterns as they are in Florida. 

Image above courtesy of Shutterstock.

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