Poleward expansion of mangroves is a threshold response to decreased frequency of extreme cold events

Regional warming associated with climate change is linked with altered range and abundance of species and ecosystems worldwide. However, less is known about how changes in the frequency of extreme events will impact ecosystems, especially for coastal environments. We used 28 years of satellite imagery to demonstrate that the area of mangrove forests has doubled at the northern end of their historic range on the east coast of Florida. This expansion is strongly associated with a reduction in the frequency of 'extreme' cold events (days < -4°C), but uncorrelated with changes in mean annual temperature, mean annual precipitation, and land use. Our analyses provide evidence for a threshold response, with declining frequency of severe cold winter events allowing for rapid poleward expansion of mangroves. Future warming may result in rapid increases in mangrove cover beyond current latitudinal limits of mangrove forests, thereby altering the structure and function of these important coastal ecosystems.