Do protected areas reduce blue carbon emissions? A quasi-experimental evaluation of mangroves in Indonesia

Mangroves provide multiple ecosystem services such as blue carbon sequestration, storm protection, and unique habitat for species. Despite these services, mangroves are being lost at rapid rates around the world. Using the best available biophysical and socio-economic data, we present the first rigorous large-scale evaluation of the effectiveness of protected areas (PAs) at conserving mangroves and reducing blue carbon emissions. We focus on Indonesia as it has the largest absolute area of mangroves (about 22.6% of the world's mangroves), is one of the most diverse in terms of mangrove species and has been losing its mangroves at a very fast rate. Specifically, we apply quasi-experimental techniques (combining propensity score and covariate matching, differences-in-differences, and post-matching bias adjustments) to assess whether PAs prevented mangrove loss between 2000 and 2010. Our results show that marine protected areas reduced mangrove loss by about 14,000ha and avoided blue carbon emissions of approximately 13 million metric tons (CO2 equivalent). However, we find no evidence that species management PAs stalled the loss of mangroves. We conclude by providing illustrative estimates of the blue carbon benefits of establishing PAs, which can be cost-effective policies for mitigating climate change and biodiversity loss.