Disturbance-driven variations in carbon stocks of an Afromontane dry forest in the Borana Woodland, Southern Ethiopia

Abstract

Dry Afromontane forests play a key role in the global carbon cycle, yet their carbon storage is increasingly threatened by human disturbance. This study quantified ecosystem carbon stocks along disturbance gradients in the Gamadu Afromontane Forest, Borana drylands, southern Ethiopia. Twenty-four 10 × 10 m plots were established along an altitudinal transect. Trees and shrubs with a diameter > 2.5 cm were measured, and biomass was estimated using site-specific allometric equations. Soil organic carbon was analyzed in 18 plots at depths of 0–15 cm and 15–30 cm. Total ecosystem carbon declined by 26.4%, from 363.0 t ha⁻¹ in low-disturbance sites to 267.1 t ha⁻¹ in highly disturbed sites. Aboveground biomass carbon dropped from 256.4 t ha⁻¹ to 115.7 t ha⁻¹, belowground biomass from 66.7 t ha⁻¹ to 30.1 t ha⁻¹, and soil carbon from 95.3 t ha⁻¹ to 63.5 t ha⁻¹. Live biomass contributed 72.5% of total carbon, soil 24.3%, and litter plus deadwood 3.2%. Deadwood carbon increased with disturbance, reflecting higher tree mortality. Biomass carbon correlated strongly with diameter at breast height (r = 0.95) and basal area (r = 0.87). These findings highlight that reducing human and livestock pressures is essential to maintain carbon stocks and enhance the climate-mitigation potential of dryland Afromontane forests.