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Mangrove forests have migrated inland over the past few decades at many locations along the northern Gulf of Mexico coast. This expansion has been attributed to factors associated with climate change, such as increased salinity resulting from sea-level rise and longer intervals between winter freezes, which can kill cold-intolerant mangrove species.
The Science Issue and Relevance: Mangrove forests have migrated inland over the past few decades at many locations along the northern Gulf of Mexico coast. This expansion has been attributed to factors associated with climate change, such as increased salinity resulting from sea-level rise and longer intervals between winter freezes, which can kill cold-intolerant mangrove species. Global atmospheric CO2 concentrations are also affected by climate change, and have increased from pre-industrial levels of about 280 ppm to approximately 391 ppm in 2011. The continued increase in CO2 concentrations predicted under future climate change scenarios is likely to enhance growth of plant species that respond positively to CO2 enrichment. In general, plants that use the C3 photosynthetic pathway are more responsive to elevated CO2 levels than plants that use the C4 pathway. The nature of interspecific interactions between plants, including competition and facilitation, that use the different photosynthetic pathways may therefore be altered under increasing CO2 concentrations. Avicennia germinans, a mangrove species that utilizes the C3 pathway, has increased in abundance at several locations in coastal Louisiana and Texas, often replacing Spartina alterniflora, a C4 grass. We are examining the effects of increasing CO2 concentration on germination and early growth of these two plant species. Results of this study will expand the information base on potential climate change effects on the distribution of coastal mangrove forest and marsh habitats. Changes in the distribution of these major habitat types will affect the quantity and quality of goods and services provided, including wildlife habitat value and carbon sequestration. The study will therefore assist resource managers in planning for future challenges under changing climate conditions.
Methodology for Addressing the Issue: These studies are conducted in greenhouse facilities designed to control atmospheric CO2 concentration. Post-disturbance scenarios in wetlands that result in the mortality of vegetation, such as sudden marsh dieback events, are simulated in the greenhouse. The effects of elevated levels of CO2 and flooding regime on the survival and growth of early life stages of A. germinans and S. alterniflora are currently being documented.
Future Steps: Future studies will examine the effects of additional physico-chemical factors, such as salinity level and nutrient concentration, on the interactions between mangrove and herbaceous species. Studies will include common plants of brackish marshes to further inform resources managers of potential plant species shifts under climate change.