Spatial Patterns of Plant Diversity, Biomass Allocation and Vegetation Biomass Carbon Storage in Major Mangrove Forests of Hainan, China.

Mangrove ecosystems are among the most productive and carbon-dense coastal forests globally, playing a critical role in plant diversity conservation and climate regulation. However, spatial variability in plant diversity, biomass allocation, and vegetation biomass carbon storage remains insufficiently quantified at regional scales, particularly in biogeographically complex regions such as Hainan Island, China. Here, we investigated four representative mangrove regions in Hainan Province: Dongzhai Port (DPMD), Qinglan Port (QPMD), Yalong Bay (YBMD), and Xinying Port (XPMD). Based on 73 field plots (0.5 ha each), we quantified species composition, community diversity, importance value index (IVI), organ-level biomass allocation (leaves, stems, and roots), and vegetation biomass carbon storage using species-specific allometric equations and published carbon concentration factors. A total of 12 mangrove species from 7 families were recorded, with Rhizophora stylosa Griff. consistently dominating across all sites (IVI range: 19.8-58.7%). Significant spatial heterogeneity was observed in all measured parameters. QPMD exhibited the highest total biomass (92.2 t ha-1) and plant vegetation biomass carbon storage (40.1 t C ha-1), whereas YBMD showed the lowest biomass (26.1 t ha-1) and XPMD exhibited the strongest species dominance (Simpson's D = 0.58). Stem biomass contributed the largest proportion (60-80%) across all sites, while root and leaf allocation varied significantly among regions, reflecting differences in community structure and stand characteristics. Vegetation biomass carbon storage patterns closely followed biomass distribution, demonstrating the dominant role of vegetation productivity in determining plant carbon accumulation. Our results reveal substantial spatial variation in mangrove diversity, biomass production, and vegetation biomass carbon storage. This study provides essential baseline information on mangrove vegetation biomass carbon stocks for region-specific conservation prioritization and climate mitigation strategies in tropical China.