Forest floor and mineral soil samples were collected in 2006 and 2021 from 6 Casuarina equisetifolia plantations in Taiwan. The aim was to estimate the total soil organic carbon (SOC) storage (TSOCCasuarina equisetifolia) of this common windbreak afforestation species on coastal sand dunes and evaluate its maximum soil C capacity. Total C concentrations of organic layers decreased with litter decomposition from 44~46% and 36~40% in the Ol and Of layers to 20~40% in the Oh layer and showed no significant difference between years. Accumulation of carbon in the forest floor reached 7~18 and 1~7 ton ha-1 at western and eastern sites, respectively. SOC concentrations were < 1% in most mineral soils from 5~60 cm in depth and decreased with soil depth. Good relationships between bulk density (BD) and SOC% were established at sites with mature forests and less typhoon disturbance. These linear relationships could be useful for assessing SOC Casuarina equisetifolias with less labor-intensive and time-consuming BD measurements. Total carbon Casuarina equisetifolias in the western and eastern coastal Casuarina-dominated forests averaged 35.6~52.4 and 23.8~36.0 ton ha-1, respectively. Typhoon disturbance significantly reduced the maximum carbon capacity, whereas drainage in flooded forests showed no significant effects on TSOCCasuarina equisetifolia. SOC saturation was observed in plantations older than 20 yr indicating that changes in forest management are required for potential additional C sequestration. Mixed species and multi-layered windbreak forests showed a positive biodiversityproductivity relationship at the Chihsingtan site, but determining how to increase the SOC sequestration duration and capacity requires further research.