4. Productivity Gradients in Mangroves
FCE researchers have found significant spatial differences in mangrove productivity; from
riverine mangrove forests with productivity rates similar to tropical rain forests to low
structure scrub mangroves that grow in nutrient-poor environments. Mangrove forests growth
and survival are greatly influenced by the impacts and legacies of hurricanes, sea-level
rise, and human impacts along coastal areas.
FCE researchers evaluate mangrove mortality at the mouth of the Shark River estuary after
the passage of Hurricane Wilma in October of 2005.
Photo taken by Victor Rivera, May 2009.
Mangrove forests in the Florida Everglades form an ecotone, which is a critical link between
freshwater marshes and the marine environments of Florida Bay and the Gulf of Mexico. These
forested wetlands provide shoreline protection against storms, "nurseries" for shrimp, fish,
and crabs, as well as habitat for several endangered and threatened species such as the
American crocodile. FCE researchers have made important contributions to our understanding
of mangrove forest structure and productivity trends. FCE researchers installed - and still
operate - the first eddy covariance tower in a riverine tall mangrove forest in 2003 to
measure the net ecosystem exchange of carbon dioxide between the mangrove forest and the
atmosphere. Mangroves remove relatively large amounts (about 1000 g of carbon per m2 per
year) of carbon dioxide from the atmosphere compared to other forest types, such as tropical
rainforests. Temporal and spatial mangrove forest productivity and structure differences are
largely controlled by large-scale disturbances, such as tropical cyclones, which can
defoliate and kill mangrove trees. Recovery rates vary with the magnitude of disturbance,
but can be accelerated by delivery of nutrients in water and soils from associated storm
surge. FCE also has a network of sediment elevation tables (SETs) that measure accretion and
relative elevation rates in coastal wetlands. Results from these devices are used in
predictive modeling efforts to project magnitudes and consequences of sea-level rise.
Further, FCE is collaborating with the Luquillo and the Mexican LTER programs to establish a
Caribbean Hurricane Research Network (CHURN) to facilitate cross-site, collaborative
research on the ecological and socio-economic factors influencing hurricane impacts on the
greater Caribbean coastal regions.
Seasonal patterns in net ecosystem carbon exchange (NEE) for the mangrove forest located
in the western Everglades. The NEE values were determined from flux tower measurements.
The carbon content in leaf litter production is also shown. Despite their harsh habitat,
mangroves remove from the atmosphere substantial amounts of carbon, with net
assimilation exceeding 1000 grams of carbon per m^2 per year. We now know the
environmental and physiological controls on mangrove ecosystems.
For further reading:
Barr, J.G., V. Engel, J.D. Fuentes, J.C. Zieman, T.L. O'Halloran, T.J. Smith, G. Anderson. 2010. Controls on mangrove forest-atmosphere carbon dioxide exchanges in western Everglades National Park. Journal of Geophysical Research 115: G02020.
Castaneda-Moya, E., R.R. Twilley, V.H. Rivera-Monroy, K. Zhang, S.E. Davis, M.S. Ross. 2010. Sediment and nutrient deposition associated with Hurricane Wilma in mangroves of the Florida Coastal Everglades. Estuaries and Coasts 33: 45-58.
Smith, T.J., G. Anderson, K. Balentine, G. Tiling, G.A. Ward, K. Whelan. 2009. Cumulative impacts of hurricanes on Florida mangrove ecosystems: Sediment deposition, storm surges and vegetation. Wetlands 29: 24-34.
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