Biomass and canopy condition indicators of short-term effects and long-term recovery of mangrove forests affected by a large oil spill

This study investigated short- and long-term effects of a large oil spill on mangrove forests in Panama on the Atlantic coast of Central America. In 1986, more than 8 million L of crude oil were released into Bahía Las Minas causing massive tree mortality of about 69 ha of Rhizophora mangle dominated mangrove forests. During the 3‐4 yr postspill, oil-affected areas were found to extend more widely, with about 300 ha of canopy thinning in surrounding forests. Oil-affected surviving mangroves had reduced leaf biomass of about 28%, with up to 12% lost each year, during 1989‐1991. Affected trees at the time were in the process of she dding upper canopy foliage. Therefore, where oil had persisted in normally anoxic mangrove soils, there was an on-going threat to the survival and recovery of both lethal and sublethal oil-affected mangrove habitat. We investigated the long-term implications of sublethal and lethal effects using NDVI measures of canopy condition from 1984 to 2023. The initial effects of the 1986 oil spill were shown as an abrupt decline in NDVI levels in oil-affected sites, with losses of about 80% in sites of tree death, and up to about 20% in sublethal affected trees. However, after one to two decades, there was substantive recovery of forest canopies with no persistent differences between oiled and unoiled mangrove forests. Long-term recovery trajectories depicted in NDVI timeseries showed sublethal-affected mangrove forest canopies had returned to prespill conditions within about 10 yr post oiling, while lethal-affected canopies had taken 15‐20 yr, nearly twice as long.