Continued loss of mangrove carbon stocks six years after a climate impact in SE Brazil

Mangroves face increasing threats from human degradation and extreme weather events, yet limited information exists on whether they can naturally recover after those disturbances. In this study, we attempted to fill this gap by assessing the total ecosystem carbon stocks (TECS) of impacted mangrove forests in Brazil six years after an extreme weather event. We hypothesized that impacted mangrove forests would show some degree of recovery in their aboveground and belowground carbon stocks, when compared to previous assessments made in 2017 (1.3 yrs after initial disturbance). Sampling impacted and pristine mangrove forests demonstrated limited or no recovery in carbon stocks over time, with a mean loss of 56.1 Mg C ha⁻¹ in the aboveground carbon stocks. Contrary to our hypothesis, we observed higher soil carbon contents but lower bulk densities in impacted areas, likely as a result of necromass decomposition and loss of mineral material from impacted soils. Mangrove TECS six years after the initial impact were on average 198 Mg C ha⁻¹ lower in dead forests compared to control sites. If all this carbon was lost to the atmosphere, the potential emissions from this event are 145.4 Mg CO₂eq ha⁻¹ per year, which is over 10 times the soil carbon burial rates in healthy mangroves of that estuary. Our work suggests that mangrove forests may have limited recovery in areas under high salinity stress, highlighting the need for site selection prior to mangrove restoration projects when desired outcomes are to restore carbon stocks.