What’s a good strategy to combat climate change and save species simultaneously? One possible approach is to focus on protecting lands that store lots of carbon and that also provide excellent habitat. A flagship example of this type of ecosystem is the mighty mangrove. Mangroves provide an incredible wealth of ecosystem services: they serve as habitat for species, and even protect coastal areas from storms. Mangrove root structures offer unique underwater habitat, safeguarding breeding grounds for fish that local people depend on. Furthermore, these coastal ecosystems store a vast wealth of carbon. The carbon that is stored in mangroves (and other coastal and marine areas) is known as blue carbon. The carbon isn’t actually blue, of course. The term blue carbon is used to distinguish the carbon stored in coastal ecosystems from that stored in terrestrial ones. Blue carbon is found worldwide and is perhaps an underappreciated part of a solution to combat global climate change.
Using policies, how can we harness the power of mangroves to store carbon and deliver climate mitigation benefits (not to mention climate adaptation benefits such as buffering from storms)? One approach is to set aside mangroves as protected areas. By drawing boundaries around mangrove habitats and preventing coastal development, perhaps we can realize some additional benefits in the form of blue carbon storage. This approach is worth investigating: are protected areas actually effective at preserving mangroves that store carbon? The first study to examine this question was published this week in Ecological Economics (Miteva et al. 2015). Miteva and her team used a quasi-experimental approach, incorporating matching and difference-in-differences methods. These approaches take into consideration the non-random locations of protected areas on the landscape. Simply comparing protected to unprotected areas would not yield accurate estimates of the causal effects of protected areas. Using matching (with both covariates and propensity scores in this case) allowed researchers to compare “apples to apples,” comparing villages that were protected with similar villages that were unprotected.
The researchers used covariates, factors correlated both with the treatments and outcomes, to select appropriate control villages. The covariates they chose included: the distance to markets (ports and cities), agricultural suitability proxies (length of rivers, slope, elevation), and socio-economic factors (e.g. poverty). They also examined how both marine protected areas (MPAs) and species management areas (SMAs) fared in terms of effectiveness. After completing a series of different statistical manipulations and robustness checks, Miteva and her team demonstrated unequivocally that overall, protected areas were significantly effective. In particular, MPAs were effective at reducing mangrove loss from both 2000 to 2006 and 2000 to 2010. However, species management areas were less effective – they did not have a significant effect during either time period.
Overall, the mangroves that were not lost because of the policy intervention of protected areas stored 13 million megatons of carbon emissions. According to the researchers’ estimates, this is equivalent to $544 million (using the social cost of carbon) and equal to taking 344,000 cars off of the road. This study is an excellent contribution to the literature, as it is the only and most current large scale evaluation of protected areas’ impacts on blue carbon. One suggestion to improve future evaluation studies is to include or control for the effects of additional policies, including changes to protected areas and other conservation interventions. At least seven known policies have changed the size or status of protected areas in Indonesia, many of which have affected coastal protected areas (see PADDDtracker.org). Although the known number of instances of protected area downgrading, downsizing, and degazettement (PADDD) events is low in this nation, it is possible that there are many other undiscovered instances. It is important for researchers to continue to explore and document these changes and consider them in analyses. If considered carefully, the incorporation of protected area dynamics could offer new insights to the evaluation literature and improve estimates of protected area performance.