Mangrove growth and biomass dynamics along the mud-dominated coast of French Guiana

Mangrove forests fringe the highly dynamic, mud-dominated Guianas coast, where wave-induced mobility of Amazon-derived mudbanks drives rapid coastal accretion and erosion. In French Guiana, this geomorphic instability reorganizes mangrove distribution, creating mosaics of successional stages in which stand development rarely approaches long-term equilibrium. However, it remains uncertain whether a single age-biomass relationship can represent contrasting coastal Avicennia-dominated stands and heterogeneous estuarine Rhizophora-dominated stands in this system. This study evaluates how effectively stand age, reconstructed from historical imagery, predicts stem diameter at breast height (DBH) and aboveground biomass (AGB) of Avicennia germinans and Rhizophora spp. along this coast, using chronosequence data spanning pioneer to mature stands. DBH was measured in the field, and AGB was estimated using locally validated allometric equations. Four empirical growth models (power, Gompertz, logistic, and monomolecular) were fitted using nonlinear least squares to describe age-structure and age-biomass relationships. Stand age strongly predicted DBH in Avicennia germinans but explained less variation in AGB and in both DBH and AGB for Rhizophora spp., and differences among growth functions were small. In this mud‑dominated setting, stand‑age models perform well for coastal mangroves but are less informative for estuarine mangroves. Under ongoing climate and environment‑driven change, this study highlights the need to complement stand age with environmental and structural covariates when modelling mangrove biomass and carbon stocks in both coastal and estuarine systems.