Carbon Dioxide Increase and Sea Level Rise Dominate the Natural Growth of Mangroves

Mangroves are essential blue carbon ecosystems with substantial potential to mitigate global warming. While human activities undeniably exert significant influence on mangrove growth, natural variables also play an important role in shaping their dynamics. Many studies focus on the effects of individual or limited factors on mangrove natural growth independent of anthropogenic deforestation, but comprehensive and large-scale assessments, particularly those considering both terrestrial and marine perspectives, remain scarce. This study examines 59 administrative areas worldwide by screening high-resolution satellite products and coastal observation records. After excluding the interference of human activities, we quantify natural mangrove changes from 1985 to 2023 using the Enhanced Vegetation Index (EVI), and evaluate the impacts of various terrestrial and marine factors, including carbon dioxide concentration, skin temperature, precipitation, solar radiation, sea level, salinity, and water temperature. Our results reveal that the EVI of naturally growing mangroves has increased by an average of 0.26±0.18% per year over the past nearly four decades, with no significant sign of deceleration, and remains commonly higher than that of adjacent non-mangrove vegetation. The annual EVI of mangroves is effectively modeled by the key environmental variables using Partial Least Squares Structural Equation Modelling (PLS-SEM), with an average determination coefficient (R2) of 0.65±0.20. Among these variables, terrestrial-based carbon dioxide increase and marine-based sea level rise are the primary drivers of natural mangrove growth. This study deepens our understanding of the natural dynamics of mangrove growth and the long-term potential of nature-based coastal solutions.