Elevation and socioeconomic factors predict biomass carbon stock through species diversity and stand structures in the homegarden agroforestry systems of the central highlands of Ethiopia

Addressing climate change and biodiversity loss under the same management program is more significant than tackling these issues separately. Agroforestry, particularly homegardens, offers a viable land-use strategy to combat both challenges. However, the direct effects of elevation, farm size, and wealth level on carbon stock in these systems, as well as their indirect effects mediated by species diversity and stand structures, remain poorly understood. In this study, we hypothesized that: (1) perennial plant species diversity and stand structures (such as basal area and stem density) directly contribute to biomass C stock in the homegarden AF systems of the central highlands of Ethiopia; (2) elevation, farm size, and wealth levels primarily affect biomass C stock indirectly, with weaker direct effects; and (3) stand structures have a more significant role than perennial plant species diversity in mediating the response of biomass C stock to these factors. We collected vegetation data from 252 sample farms, randomly selected from three purposively chosen kebeles. Structural equation modeling (SEM) was used to analyze the direct and indirect relationships among elevation, socioeconomic factors, species diversity, stand structure, and aboveground biomass C stock. The results indicated that basal area and stem density have the strongest direct positive effects on biomass C stock, highlighting the critical role of stand structure in determining biomass C stock. Elevation influenced biomass C stock directly, but this effect was largely mediated through stand structures (stem density and basal area), supporting our hypothesis that elevation affects biomass C stock indirectly. Farm size also had a significant direct effect on biomass C stock, with indirect effects through stem density and basal area; however, it did not impact biomass C stock via perennial plant species diversity. Wealth levels influenced biomass C stock both directly and indirectly, with indirect effects mediated by perennial plant species diversity, stem density, and basal area. These findings highlight that stand structural attributes, particularly basal area and tree density, are the most influential determinants of biomass C stock in Ethiopian homegarden AF systems. Elevation and socioeconomic variables mainly affect biomass C stock indirectly, emphasizing the importance of maintaining stand structures and enhancing species diversity to optimize carbon sequestration and ecosystem services in agroforestry landscapes.