Estimation and Mapping of Above and Below Ground Biomass Distribution in Southern Guinea Savannah Zone of Taraba State, Nigeria

Abstract

This study assessed temporal and spatial variations in above- and below-ground biomass (AGB and BGB) in the Southern Guinea Savannah of Taraba State, Nigeria, from 1987 to 2024 using multitemporal Landsat data, Normalized Difference Vegetation Index (NDVI) modeling, and soil organic carbon (SOC) analysis. AGB was derived from NDVI-based regression equations, while BGB was estimated using SOC as a proxy following the modified approach. Results show a marked decline in vegetation productivity and carbon storage over the 37-year period. AGB ranged from 0–84.82 t ha⁻¹ (1987) to 0–95.20 t ha⁻¹ (2024), with low-biomass zones expanding from 36.8 % to > 60 % of the landscape. Mean biomass peaked at 39.79 t ha⁻¹ in 2014 before falling to 32.39 t ha⁻¹ in 2024, indicating renewed degradation after a brief recovery phase. SOC values varied from 0.36–12.2 g kg⁻¹, highest in forest and riparian sites, confirming strong vegetation–soil carbon coupling. ANOVA results (F = 49.129, p < 0.001) revealed significant inter-year differences, and Tukey’s HSD indicated a major decline between 2014 and 2024 (p < 0.001). The NDVI–AGB correlation weakened progressively (R² = 0.958 → 0.743), reflecting landscape fragmentation and ecosystem instability. Overall, total ecosystem biomass decreased by over 40 %, demonstrating severe loss of carbon sequestration capacity. These findings highlight the transition of the Southern Guinea Savannah toward a degraded ecological state and emphasize the urgency of community-based reforestation, assisted natural regeneration, and the integration of biomass–carbon monitoring into Nigeria’s climate-adaptation and land-restoration policies.