<title>Abstract</title> Recent studies suggest that mangrove forests have an exceptional capacity of capturing and storing carbon. However, the relationship between this ecosystem service and environmental factors is less studied. Here, we evaluate how environmental conditions influence tree community composition and carbon storage in Mallorquin swamp, an urban mangrove ecosystem in Barranquilla, Colombia. We measured mangrove tree community composition, vegetation structure, soil pH and salinity in 18 circular plots located in areas with Low, Medium, and High salinity. Using published allometric equations and wood density database, we estimated total aboveground biomass. Our results show significant soil salinity differences among the sampling areas, especially during the dry season. Nonetheless, we found small differences in soil pH across stations regardless of the season. Avicennia germinans was mostly associated with Low salinity areas, Laguncularia racemosa with Medium salinity areas, and Rhizophora mangle in High salinity areas. Observed differences in tree height, abundance, and vertical structure were noteworthy, with the Low salinity area hosting significantly taller and bigger trees and a larger carbon stock. Carbon stock estimates were 4098.6 Mg C for Low, 104.6 Mg C for Medium, and 1761 Mg C for High salinity areas. These findings highlight the significance of local environmental factors in mangrove conservation efforts, particularly in urban areas like Barranquilla; contributing to our understanding of the relationship between mangrove ecosystems and carbon cycling; emphasizing the need for targeted conservation efforts to protect these vital coastal habitats.