Current methods to evaluate net primary production and carbon budgets in mangrove forests

Mangrove forests are a dominant feature of tropical and subtropical coastlines; however, anthropogenic pressures have reduced the global extent of these forests to <50% of the original total cover. These coastal wetlands are very productive and efficient C sinks, contributing to C biogeochemistry in coastal oceans and providing a wide array of ecosystem services. We review the most common methods used to estimate net primary productivity (NPP) and how they are used to determine C budgets. A general explanation about the eddy covariance method to evaluate the net ecosystem exchange (NEE) is included in the context of traditional above- and belowground biometric (summation) methods and the NEE relationship to net ecosystem production. We use recent NEE data and biometric information from a neotropical riverine mangrove forest to underscore the importance of organic and inorganic matter exchange between the forest and estuarine and coastal waters when assessing the relative contribution of NEE and NPP to the net ecosystem C budget. We also revise published information where C fluxes and storage have been estimated and summarize the methods used to facilitate the identification and interpretation of fluxes in the context of whole C budget estimation. We finally present an integrative approach based on existing methods that could serve as a guide to develop comparative mangrove C cycling studies in mangrove ecosystems across forest ecotypes and ecogeomorphic settings.