Collaborative Research: Climate variability causes catastrophic loss of a foundation species; secondary succession pathways determine the consequences

Variability in weather can have strong effects on ecological communities, especially near geographic range limits. Mangroves (salt tolerant trees) and salt marsh plants (mostly grasses) both live on the coast, but mangroves cannot tolerate hard freezes and so are more common in the tropics. A hard freeze will kill most mangroves, leaving behind bare sediment. In the following years, these areas of bare mud may become occupied by either marsh plants or mangroves, or remain bare mud. Because people rely on coastal wetlands for many “services”, such as protection from storms, a better understanding of which plants recover after a freeze, and how quickly they recover, will help coastal communities understand if mangroves near their high-latitude range limits are reliable “green infrastructure” that can be counted on to protect coastlines from storms and erosion. This knowledge will help guide the design and management of wetland restoration and green infrastructure projects. More generally, this project will provide new insights into how ecological systems respond to and recover from severe weather events. The project builds on more than ten years of research on the Texas coast at an experimental site (ten, 24 x 42 m plots) in which mangroves were thinned to create plots ranging from zero to 100 percent mangrove cover, and at several survey sites dominated by either mangroves or marsh plants. A hard freeze in 2021 killed most of the mangroves at these sites. This research will document the “successional sequence”, which plant species recover after a hard freeze, and how quickly they reestablish, This will be done by continuing to sample existing experimental and survey sites. Additionally, the research will manipulate the successional sequence at the experimental site to find out how different types of vegetation (marsh plants versus mangroves) affect sediment loss versus gain. This will be done by removing mangrove seedlings in some experimental plots to create some plots that are dominated by marsh plants and others that are dominated by mangroves, and measuring how this vegetation manipulation affects elevation change and intertidal sediment dynamics. Last, the research will document how higher trophic levels, especially crabs and snails, influence the dynamic interactions between wetland plants and intertidal sediment loss or gain. This will be done with a combination of monitoring and laboratory experiments. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.