Data for: Seedling Density as a Key Determinant of Topsoil Organic Carbon and CNP Stoichiometry in Intertidal Mangrove Ecosystems: Insights from Avicennia marina Stands

This dataset contains field survey and soil biogeochemical data collected from a monodominant Avicennia marina mangrove forest on Techeng Isle, Zhanjiang, China, during October 2020. It supports the findings reported in the associated manuscript.The dataset includes:Mangrove population structure: tree density, average height, basal diameter, crown width, and number of individuals across five size classes (seedlings, saplings, small trees, medium trees, large trees) from 30 quadrats (5 m × 5 m) along three seaward–landward transects.Topsoil properties at two depths (0–10 cm and 10–20 cm): soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and calculated C:N:P stoichiometric ratios (C:N, C:P, N:P).Environmental variables: intertidal elevation, sediment type (sand / sand‑mud mixture), sediment temperature, salinity, water content, and pH measured in each quadrat.Derived indices: Root Density Index (RDI) and Anoxia Potential (AP), which were integrated into structural equation modelling to test causal pathways linking seedling density to soil carbon and nutrient accumulation.All data are provided as a single Excel file with multiple sheets, including raw measurements, summary statistics, and the derived indices. The data processing and statistical analyses (random forest, redundancy analysis, variance partitioning, SEM) are fully reproducible from this dataset.For any further information, please contact the corresponding author: [e-mail].