Mangrove Blue Carbon in the Face of Deforestation, Climate Change, and Restoration

Abstract

Coastal wetlands have disproportionately high carbon densities, known as blue carbon, compared to most terrestrial ecosystems. Mangroves and their blue carbon stocks are at risk globally from Land Use and Land Cover Change (LULCC) activities such as aquaculture, alongside biophysical disturbances such as sea-level rise and cyclones. Global estimates of carbon emissions from mangrove loss have been previously unable to differentiate between the variable impacts of different drivers of loss. This Review discusses the impacts that different LULCC activities and biophysical disturbances have on carbon stocks (biomass and soil) and carbon fluxes (CO 2 and CH 4 ). The dynamics of carbon stocks and fluxes depends on the type of LULCC; aquaculture often results in biomass and soil carbon removal, and some forms of agriculture can substantially increase methane emissions. Natural disturbances

Future carbon emissions from global mangrove forest loss

“…We assumed that future loss rates due to each of the five drivers were proportional to their historical contributions. Therefore, our predictions may overestimate emissions in regions where mangrove deforestation rates are slowing because of policy changes (Friess, Krauss, et al, 2020, Friess, Yando, et al, 2020; Richards et al, 2020). Changes in the magnitude of drivers of mangrove loss are likely to occur in the future, implying that our assumption of linearity in predictions may not happen.…”

“…Under a BAU scenario, global emissions from mangrove loss could reach 2,391 Tg CO 2 eq by the end of the century (2010–2100), or 3392 Tg CO 2 eq if considering the lost opportunity for soil carbon sequestration. Previous estimates of mangrove emissions for the same period vary enormously, between 630 and 40,230 Tg CO 2 eq (Friess, Krauss, et al, 2020) . Our projection lies towards the lower end of this range, and we consider it more accurate because of the inclusion of land‐use drivers, time lags and foregone future sequestration that were not considered in previous studies.…”

“…We assumed that future loss rates due to each of the five drivers were proportional to their historical contributions. Therefore, our predictions may overestimate emissions in regions where mangrove deforestation rates are slowing because of policy changes (Friess, Krauss, et al, 2020Richards et al, 2020). Changes in the magnitude of drivers of mangrove loss are F I G U R E 3 Emission reductions (Tg CO 2 eq ) that could be achieved from (a) management of agriculture/aquaculture and shore stabilisation in the West Coral Triangle and (b) decrease in erosion through shore stabilisation, mangrove protection to avoid clearing and restoration of mangroves affected by tropical storms in the Tropical Northwest Atlantic likely to occur in the future, implying that our assumption of linearity in predictions may not happen.…”

“…Management actions, such as avoiding deforestation or restoring hydrological connectivity, can reduce CO 2 emissions from mangrove loss and enhance the sequestration potential of disturbed forests (Friess, Krauss, et al, 2020; O’Connor et al, 2020). But management actions should be guided by predictions of future emissions, not just carbon storage.…”

Relationships between above- and below-ground carbon stocks in mangrove forests facilitate better estimation of total mangrove blue carbon

“…Components of mangrove carbon stocks can only be roughly estimated using empirical average values and conversion coefficients. In addition, accurate estimation of total mangrove carbon stock is limited due to the unclear relationship between above- and below-ground carbon stocks [ 34 , 73 ].…”