Compare salt marshes and mangrove forests and explain why mangrove forests are such critical habitats on high energy coasts.​

Explanation:Coastal wetlands in the southeastern U.S. provide many important ecosystem goods and services. In addition to supporting important fish and wildlife habitat, they maintain coastal fisheries, store carbon, improve water quality, protect coastlines, and provide recreational opportunities. In many ways, coastal wetlands are dynamic and resilient ecosystems; however, they are being subjected to tremendous environmental change at the regional (e.g., hydrologic alterations, nutrient enrichment) and global scale (e.g., climate change).

One aspect of global change that is expected to have a substantial impact on coastal wetlands is winter climate change. Salt marshes and mangrove forests are common coastal wetland ecosystem types that occupy similar estuarine environments but have different climatic tolerances. In warmer climates, mangrove trees often outcompete salt marsh grasses. However, mangrove forests are sensitive to freezing temperatures, and within the region, mangrove forests are currently found only in Florida, Louisiana, and Texas (though isolated individuals have been reported in Mississippi). Salt marshes are more dominant along colder coastlines where mangroves are not able to survive freeze events. Future climate change is expected to result in increased winter temperatures and, potentially, reductions in the intensity of freeze events which could lead to mangrove forest replacement of salt marsh in parts of the Gulf of Mexico and southeastern Atlantic coast.

From a functional perspective, salt marsh grasses and mangrove trees are foundation species that control ecosystem dynamics and, in stressful and highly dynamic environments, provide the structural properties needed by other species; hence, the ecological and conservation implications of grass-to-tree conversions in coastal wetlands could be large (in both positive and negative ways). Dr. Mike Osland, USGS Research Ecologist and GCPO LCC staffer, along with 4 collaborating scientists, has initiated a study that addresses the following question: how might winter climate change impact the distribution and abundance of salt marshes and mangrove forests in the southeastern U.S.?

Their results begin to illustrate the vulnerability of salt marshes in the southeastern U.S. to mangrove forest expansion and quantify the amount of salt marsh habitat within each state that could be impacted by mangrove forest expansion under various winter climate change scenarios. The preliminary results are striking in terms of the potential for mangrove forest range expansion and coastal marsh displacement in the region. The hope is that these analyses stimulate additional discussion, research, and planning regarding the potential ecological and conservation implications of winter climate change for coastal wetlands in the southeastern U.S.