Mangroves vs. Salt Marshes: Mangrove Forest Range Expansion at the Expense of Salt Marshes

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Winter climate change has the potential to have a large impact on coastal wetlands in the southeastern United States.

Mangrove forest range expansion at the expense of salt marshes
Mangrove forest range expansion at the expense of salt marshes

The Science Issue and Relevance: Winter climate change has the potential to have a large impact on coastal wetlands in the southeastern United States. Warmer winter temperatures are expected that will lead to reductions in the intensity of freeze events and mangrove forest range expansion at the expense of salt marshes (i.e., woody plant encroachment into tidal grasslands) in Texas, Louisiana, and parts of Florida. The objective of this research is to better evaluate the ecological implications of mangrove forest migration and salt marsh displacement as well as advance models to improve our understanding of: (1) the current distribution of mangrove forests relative to salt marshes; and (2) the potential for future winter climate change-induced mangrove forest replacement of salt marsh. The research is being conducted across the U.S. Gulf of Mexico coast.

Methodologies for Addressing the Issue: This research includes various components: (1) Determining the belowground and ecosystem carbon implications of mangrove replacement of salt marsh?: This component focuses primarily on the belowground and ecosystem carbon implications of mangrove replacement of salt marsh. Plant, soil, and porewater data have been collected across structural gradients in three mangrove-marsh ecotones in Texas, Louisiana, and Florida. (2) Models of the mangrove forest distribution and abundance: Climate and coastal wetland data were used to identify ecological thresholds and develop models to predict future mangrove expansion in the southeastern United States. (3) Mangrove forest resistance and resilience to winter climate extremes: Mangrove forest damage and recovery from winter climate extremes will be quantified and models will be built that identify resiliency hot spots. Data sources include field surveys following extreme freeze events that occurred in 2014, historical estimates of mangrove expansion and contraction, and historical climate data.

Exposure: Predicted future mangrove forest presence and abundance (2070-2100)
Exposure: Predicted future mangrove forest presence and abundance (2070-2100)

Future Steps: For Component 1: Documentation of project results is currently being submitted for publication. For Component 2: Microclimatic gradients are being used to evaluate the identified ecological thresholds. For Component 3: Data are being analyzed and results are being compiled for publication/dissemination.

Publications:

Osland, M. J., N. Enwright, R. H. Day, and T. W. Doyle. 2013. Winter climate change and coastal wetland foundation species: salt marshes versus mangrove forests in the southeastern U.S. Global Change Biology 19:1482-1494.

Osland, M. J., R. H. Day, J. C. Larriviere, and A. S. From. 2014. Aboveground allometric models for freeze-affected black mangroves (Avicennia germinans): equations for a climate sensitive mangrove-marsh ecotone. PLoS One 9(6):e99604.

Osland, M. J., N. Enwright, and C. L. Stagg. 2014. Freshwater availability and coastal wetland foundation species: ecological transitions along a rainfall gradient. Ecology 95:2789-2802.

The tipping point: where salt marshes are replaced by mangrove forests
The tipping point: where salt marshes are replaced by mangrove forests

Lovelock, C. E., K. W. Krauss, M. J. Osland, R. Reef, and M. C. Ball. In press. The physiology of mangrove trees with changing climate.in G. H. Goldstein and L. S. Santiago, editors. Tropical tree physiology: adaptations and responses in a changing environment. Springer, New York, New York.