Shifting habitats and ecosystem services
Climate-driven habitat shifts are reshaping ecosystems globally, including in the northern Gulf of the United States. One example of this phenomenon in the region is the expansion of mangroves into areas historically dominated by salt marshes. Warmer winters are reducing freeze events that once limited mangrove growth, allowing these woody, tropical species to expand poleward and outcompete freeze-tolerant marsh grasses. This transition represents a major ecological shift that could significantly alter wetland structure, function, and ecosystem service delivery.
Mangrove distribution, especially at the range limits for these species, is highly dynamic. In expert elicitation exercises with wetland scientists and coastal managers, we built an up-to-date mangrove distribution map and found that expert perceptions differed from existing spatial information most frequently at mangrove range limits. Further, these experts recommended methodological refinements and improved spatiotemporal data regarding changes in mangrove structure and abundance near northern range limits in the southeastern USA (Bardou et al., 2023). Our updated map is publicly available on the Mangrove Explorer clearinghouse.
Given structural and functional differences between these two wetland types, we sought to understand if mangroves and salt marshes offer distinct ecosystem services to benefit coastal societies. We reviewed the current understanding of the effects of mangrove range expansion and displacement of salt marshes on ecosystem services (e.g., carbon sequestration, wildlife habitat, storm protection, erosion reduction, water purification, fisheries support, recreation) in the southeastern United States, and identified emerging research needs in this space. We found that there are ecological trade-offs, where mangrove expansion and marsh displacement can produce beneficial changes in some ecosystem services, while simultaneously producing detrimental changes in other services. Thus, there can be local-scale differences in perceptions of the impacts of mangrove expansion into salt marshes. For very specific local reasons, some individuals may see mangrove expansion as a positive change to be embraced, while others may see mangrove expansion as a negative change to be constrained (Osland et al., 2022).
To estimate how mangrove expansion will look in the future, we projected coastal wetland vegetation distribution and structure for the period 2071-2100. Mangrove presence will dramatically increase in the northern Gulf and southeast Atlantic coast of the US, especially under higher carbon emissions scenarios. This impending transformative change of coastal habitats necessitates further study of mangrove range dynamics and better integration of ecological data with societal needs and perceptions (Bardou et al., 2024).
