Belowground Responses of Avicennia germinans to Mild Freeze Events: Implications for Blue Carbon Storage and Restored Wetlands

Black mangroves are essential to Louisiana’s coast, protecting against edge erosion, buffering wave action, and sequestrating carbon. However, their freeze-intolerance makes them vulnerable to polar vortex excursions. This research investigated impacts of a mild freeze event on Avicennia germinans' belowground biomass in restored and natural wetlands. Total and vertical distribution of live belowground biomass were measured. Twenty-four cores were collected before and after the mild freeze event of December 2022 at three locations in West Belle Barrier Island: two within a restoration area and one within naturally occurring mangroves. Cores were 30-cm deep and were divided into 2-cm sections for analysis. The natural wetland had 4 to 7 times more belowground biomass than restored sites. After the freeze, its biomass decreased by 14%, while restored sites decreased by 82% (edge) and 22% (inland). Results indicate restoration status and impacts of low temperatures should be considered when modeling mangrove-derived blue carbon.