Rehabilitation of Woody Species Diversity and Biomass Carbon Stock in Goro Exclosure Site, Central Ethiopia

Abstract

Area exclosures, established to restrict human and animal activities in degraded landscapes, are vital for promoting natural regeneration of plant species. This study evaluates an area exclosure in Goro, where such management is uncommon, by comparing woody plant diversity, structure, regeneration patterns, and biomass carbon storage with adjacent open grazing land. Woody species were sampled using systematic transects within 20 m × 50 m plots in both sites. Species diversity, richness, evenness, structural attributes, and regeneration status were assessed. Biomass and carbon stocks were estimated using non-destructive methods, and correlations among biomass, carbon stocks, and richness were analyzed. The exclosure exhibited significantly higher woody plant diversity and richness than the grazing area. Regeneration in the exclosure followed an inverted ‘J’-shaped DBH distribution, indicating healthy regeneration. Above-ground biomass (AGB) and carbon stocks averaged 44.21 ± 16.1 t/ha and 25.80 ± 9.41 t/ha in the exclosure, versus 44.73 ± 44.6 t/ha and 26.07 ± 25.99 t/ha in the grazing land. Pearson correlation analysis revealed that biomass and carbon stock are almost perfectly correlated (r ≈ 0.999, p < 0.001), reflecting the direct dependence of carbon content on biomass. In contrast, species richness showed a weak positive correlation with both biomass (r ≈ 0.15) and carbon (r ≈ 0.15), which was not statistically significant. Area exclosures enhance woody plant diversity and regeneration, though biomass and carbon accumulation are similar. Thus, the study suggests that exclosures and open grazing lands may currently provide comparable ecosystem services, but exclosures hold promise for greater biomass and carbon storage as vegetation structure and species composition develop further over time While short-term carbon gains may be modest, the ecological trajectories initiated by exclosures align well with national objectives for biodiversity conservation, climate change mitigation, and sustainable land management.