When not threatened with removal from coastal development, mangroves in south Florida routinely bear the brunt of Atlantic Hurricanes. Mangroves are one of nature’s most effective means of hurricane protection, however they are not immune to damage sustained from powerful storms, such as Hurricane Irma. This study assessed the initial damage and continues to monitor mortality and early recovery of mangrove forests in the Lower Florida Keys and Ten Thousand Islands following direct hits by Irma in September 2017. Researchers from the Fish and Wildlife Research Institute are also monitoring the thickness, composition, and gradual thinning of the storm-surge deposit that was left in the forests following the hurricane.
Mangrove forests grow along many coastal zones with temperate to tropical climates, and many of these areas experience periodic damage caused by tropical cyclone winds and storm surges. These severe storms can defoliate the canopy, snap branches and trunks, damage bark and uproot trees, resulting in the destruction of the canopy in a mangrove forest. Mangroves can also be killed by altered hydrology (long-term standing water or blocked tidal flow) and sedimentary storm-surge deposits long after a hurricane has passed. The mud or water can prevent oxygen uptake by their aboveground root adaptations, which then suffocates belowground root stock. Since Hurricane Irma has passed, FWRI researchers have been contacted by several restoration partners for advice on the cause and recommended solutions for mangrove restoration following Irma. Although natural forests should be allowed to recover on their own, mangrove forests with stress or die-offs due to altered hydrology from human impacts (roads, mosquito ditches, etc.) may benefit from restoration efforts. Understanding the mechanisms behind stress and delayed mortality has allowed researchers to make recommendations for restoration efforts for these specific areas of stress. The vegetation is being studied over the course of several years because initial damage assessments often underestimate damage from hurricanes due to delayed mortality in trees, caused by storm-surge deposits or altered hydrology, which is difficult to assess immediately following a hurricane.
This information will help provide direct evidence of hurricane impact and recovery trajectories in coastal wetland ecosystems in Florida. The data will be shared with coastal ecosystem managers in order to enhance management and response planning for large natural disasters in Florida such as hurricanes.
Map showing the location of field sites in proximity to the path of Hurricane Irma. Pre-existing study sites are given for each area in the inset boxes at right.
Example of severe damage to a mangrove forest in the Ten Thousand Islands due to Hurricane Irma. This site was directly under Irma’s path as a Category 3 storm and was found to have complete loss of leaves in the canopy (defoliation) and numerous downed trees. Canopy cover is typically 80-100% in non-impacted forest.