Many species of plants and animals have declined in abundance and distribution or become extinct because of anthropogenic changes to the environment. Mangroves, trees that form dense coastal forests in tropical and subtropical areas, have declined in areal coverage by approximately one third since 1950 largely because of coastal development and logging. The loss of mangrove forests is particularly worrisome because they provide important ecosystem services to humans in the forms of hurricane protection, wave buffering, and carbon storage, and they can provide crucial nursery habitat for many fishes and invertebrates.
A recent study by Cavanaugh and colleagues, however, shows that global warming may be helping mangroves expand their distribution into previously hostile environments. The authors examined 28 years of satellite images of the northeast coast of Florida, near Jacksonville, and found that mangroves have doubled their areal coverage in the region in that time span by gradually expanding into habitats to the north. This is surprising because mangroves are thought to be limited by the cold temperatures of more northerly temperate climates. The authors explain the distributional shift by showing that the frequency of “extreme” cold events (days colder than -4 °C) has decreased in the region as the climate has warmed, allowing the mangroves to slowly expand their range. This interesting finding appears to be a good thing for the health of mangrove forests, but it could have negative consequences for other valuable coastal habitats (e.g., salt marshes) that could be taken over by mangroves.
Cavanaugh K, JR Kellner, AJ Forde, DS Gruner, JD Parker, W Rodriguez, IC Feller (2014) Poleward expansion of mangroves is a threshold response to decreased frequency of extreme cold events. Proceedings of the National Academy of Sciences 111:723-727