Role of sacred groves in southwestern Nigeria in biodiversity conservation, biomass and carbon storage

Sacred groves are remnants of primary forests with rich biological diversity, protected by indigenous communities. Their role in carbon sequestration and provision of other ecosystem services is being recognized. We investigated four sacred groves (Idanre Hills, Igbo-Olodumare, Ogun-Onire, and Osun-Osogbo) in southwestern Nigeria for biodiversity conservation, biomass production, and carbon storage. A total of 32 temporary sample plots of 800 m² each were laid across all the sacred groves. Within each plot, all trees with dbh greater or equal to 10 cm were identified, and their diameters and heights measured. Saplings and seedlings were assessed within 100 m² and 25 m² sub-plots, respectively. Non-destructive methods were employed in estimating volume, biomass production, and carbon storage. Shannon–Wiener diversity index, Margalef index, and tree species richness in the four groves ranged from 2.63–3.55, 5.64–10.02, and 41–85, respectively, and differed significantly. The four groves were sanctuaries for many indigenous tree species of immense social, religious, ecological, and socio-economic importance. The high densities of seedling and sapling, together with the inverted-J tree diameter distributions, are indications of active regeneration and healthy ecosystem. Mean volume was high (range 244.99 to 343.08 m³ ha⁻¹). The biomass (range 87.8 to 231.85 t ha⁻¹) and carbon stock (range 43.9 to 115.9 t ha⁻¹) of the groves revealed their potentials for climate change mitigation through atmospheric CO₂ sequestration. Thus, besides being an effective biodiversity conservation method, sacred groves are important carbon sink. This calls for further conservation of sacred groves to serve as long-term carbon storage mechanism.