Tree species diversity and conservation across disturbance and bioregion types in forest patches outside protected areas in tropical Africa

In West and Central Africa, most forest patches lie outside protected areas and are managed by local communities who depend on their ecosystem services. Yet, their role in conserving tree diversity under varying bioregions and disturbance pressures remains poorly documented. We investigated tree community diversity and structure in nine forest patches across the Guineo-Sudanian and Guineo-Congolian bioregions using 121 plots (2500 m² each) along edge-interior gradients. We recorded anthropogenic disturbances (wildfire, logging, agriculture, invasive plants, footpaths) and measured the diameter at breast height (DBH) for all trees ≥ 10 cm. We identified 382 tree species, of which ∼10 % are globally threatened. Despite their small size, the patches contribute 15–33 % of national tree species richness in the four countries studied. Tree density and basal area were consistently lower than reference values from nearby protected forests, ranging from 186 to 422 stems.ha⁻¹ and 12.36–23.17 m².ha⁻¹ in the Guineo-Sudanian, and 263–476 stems.ha⁻¹ and 12.20–34.75 m².ha⁻¹ in the Guineo-Congolian. Alpha diversity was higher in the Guineo-Congolian than in the Guineo-Sudanian, and beta diversity was generally high among forest patches. Disturbances were concentrated at forest edges and negatively affected tree structure and composition, irrespective of ownership. Our findings show that small, unprotected forest patches make a disproportionate contribution to national and regional tree diversity but remain vulnerable to disturbances. Strengthening customary rights and inclusive governance under “Other Effective area-based Conservation Measures” (OECMs), coupled with locally adapted forest zoning, could enhance both biodiversity conservation and community livelihoods. • Forests outside PAs hold 15–30 % of national tree flora in West and Central Africa • Forests outside PAs in Africa harbour up to 38 % of national threatened tree species • Diversity and structure across forests outside PAs are less than climax references • Existing community-based governance cannot ensure long-term forest integrity • Empowering the Community-led management is vital for conserving forests outside PAs