Mangroves, tropical costal trees, are moving north along the Florida coast.
Written by ISA BCMA Danny Lippi for “Roundtable” the publication from the SMA – Society for Municipal Arborists.
Stretching more than 3000 miles from south entral Florida, south to the coastal amazon rainforest in Brazil, the tropical mangrove swamp is one of the largest continuous ecosystems in the western hemisphere. Historically the northernmost mangroves on the atlantic coast of Florida were just north of the Indian River lagoon around Kennedy Space Center, approximately 175 miles south of the Georgia border with a few small single pioneers reaching into north Florida. But according to recent data presented by the GTM-NERR (Guana Tolomato Matanzas-National Estuarine Research Reserve, a division of NOAA and the Department of Environmental Protection) the northernmost black mangrove (Avicennia germinans) is now located in northern St. Augustine, approximately 60 miles south of the Georgia border on the atlantic coast. According to a 2013 study from the Smithsonian Environmental Research Center using data gathered over the last 28 years, “…the area of mangrove forests has doubled at the northern end of their historic range on the east coast of Florida.”1 This expansion appears related to a lack of consistent extreme periods of cold.
Until 10 years ago mangroves were an issue handled largely by arborists and developers in south Florida. Most arborists and landscapers in north Florida rarely encountered mangroves, but as current environmental trends continue, arborists in once freeze-prone areas of northern Florida are becoming more well versed with managing the persistent tropical mangroves. Black mangroves 20-30 feet in height are not now uncommon in north Florida. But thanks to the “Mangrove Trimming and Preservation Act of 1996” few broadleaf trees in the United States are as protected as mangroves are in Florida. According to a panel of attorneys at a recent state seminar on mangrove management in West Palm Beach, not even sequoias on the west coast are as heavily protected. Improper pruning, removal or damage carries a minimum fine of $5,000 per tree, a fee that makes even wealthy developers think twice before clearing waterfront parcels for their even wealthier clients. This means more homeowners are hiring qualified arborists to trim their mangroves to maintain their waterfront views. As with other trees, proper pruning is critical for mangroves to maintain proper structure and good health.
The most numerous species of mangrove in Florida is the red mangrove (Rhizophora mangle), but the most abundant mangrove in north Florida is the black mangrove due to its greater cold tolerance threshhold. All three mangrove species including the very cold sensitive white mangrove (Laguncularia racemosa) can now be found in St. Johns county, approximately 75 miles south of the Georgia border on the atlantic coast. Dominated by smooth cord grass (Spartina alterniflora) cold tolerant salt marsh is slowly being outcompeted for sunlight by the increasingly taller and more dense mangrove swamp. As the northern movement of mangroves continues this will have large implications for Florida’s ecology and economy. Because a large number of plants and animals, including many species of fish, are associated with either only mangrove swamps or salt marshes a distinct change in both coastal flora and fauna is currently taking place. Mangroves sequester more carbon dioxide than marsh grasses, but marshes produce much larger amounts of detritus, the organic fuel for fisheries. Estuaries are the nurseries for the oceans and fisheries are Florida’s second largest economy after tourism. Both commercial and recreational fishing combined generate approximately 10 billion dollars annually in revenue for the state, more than the citrus industry.2 Money talks and private home owners as well as private and governmental organizations are paying close attention to the northward expansion of the tropical mangroves.
1 Cavanagh, Kellner, et al. Poleward expansion of mangroves is a threshold response to decreased frequency of extreme cold events. Smithsonian:vol. 111 no. 2, 723-727. 2013.
2 Coastal Systems and the Human Landscape. Dir. Martin Main Phd.. UF-IFAS. 2002. DVD.