Assessment of Carbon Stock and Biomass in the Secondary Forests of the Omo Forest Reserve, Ogun State

Forest carbon stocks are critical components of Nigeria's climate change mitigation potential under the Paris Agreement, and professional assessment of secondary forest carbon in Omo Forest Reserve, Ogun State, provides essential data for the national REDD+ programme. This study assessed the above-ground biomass carbon stock and below-ground carbon pool in secondary forest stands of varying age classes (5 to 10 years, 10 to 20 years, and above 20 years) in Omo Forest Reserve. Systematic vegetation plots (25m x 25m) were established in 12 stands representing the three age classes. Diameter at breast height and total tree height were measured for all trees with DBH above 5 cm. Above-ground biomass was estimated using allometric equations validated for West African secondary forests. Below-ground biomass was estimated as 26% of above-ground biomass using IPCC default ratios. Soil organic carbon (0 to 30 cm) was measured by the Walkley-Black method. Total ecosystem carbon increased significantly with stand age: 5 to 10-year stands averaged 78 Mg C/ha, 10 to 20-year stands averaged 142 Mg C/ha, and above 20-year stands averaged 218 Mg C/ha. Soil organic carbon contribution declined proportionally with increasing stand age as above-ground stocks accumulated. Annual carbon sequestration rates were estimated at 8.4 Mg C/ha/year for the youngest class. The study provides the first age-stratified carbon stock assessment for Omo Forest Reserve and recommends its integration into Nigeria's REDD+ monitoring, reporting, and verification system.

Keywords: carbon stock, biomass, secondary forest, Omo Forest Reserve, REDD+