Biomass carbon stocks, socio-ecological determinants and economic valuation in Ethiopian traditional agroforestry practices

There are diverse ranges of agroforestry (AF) practices which are generally categorized into various types based on their key components. Homestead AF (HSD-AF) and dispersed trees in perennial crop AF (DTPC-AF) practices are among the different AF practices in the country. Numerous studies have emphasized the need to fill the gap of information regarding the amount of carbon (C) stored in various AF land use systems and its relationship to socio-ecological variables, however, there was scarcity of such information for HSD-AF and DTPC-AF practices in Ethiopia. This study evaluated biomass C storage and its socio-ecological drivers in homestead AF (HSD-AF) and dispersed trees in perennial crop AF (DTPC-AF) employing a multi-stage design. Results show HSD-AF has about 123% higher stem density than DTPC-AF (p < 0.001), while DTPC-AF has a mean diameter at breast height (DBH) twice that of HSD-AF. Biomass C contributions are dominated by native species, which make up 75.3% of basal area (BA). Their BA in HSD-AF was 60.2% higher than that in DTPC-AF. Household wealth significantly influences stand density, with wealthier households maintaining higher stem numbers (p < 0.001). HSD-AF practices demonstrate significantly higher (p < 0.01) aboveground and total biomass carbon (TBC) stocks than DTPC-AF. Native species contribute around 70% of biomass C in both practices, with trees accounting for over 60% of aboveground biomass carbon (AGBC). The combined AF practices sequester an average of 222.77 Mg CO₂ equivalent per hectare, with an estimated economic value exceeding USD 1000 per hectare. Linear mixed model revealed that AF significantly enhanced AGBC (β = 9.25, p < 0.01) and TBC (β = 7.68, p < 0.05). Higher altitude negatively impacts AGBC and TBC, while slope reduces all biomass components. Wealthier households positively influence AGBC and TBC. Interaction effects demonstrate that AF reduces the detrimental impacts of altitude on TBC and reduces slope-related limitations on biomass C components. Stand density and BA strongly influenced biomass C stocks, with BA exerting a more pronounced effect. Native species contribute more significantly to AGBC and TBC than exotic species. The models explain a moderate proportion of variance in biomass C stocks, with marginal R² values of up to 51%. The study highlights that AF land use systems significantly contribute to biomass C storage, aiding climate change mitigation. It also emphasizes the impact of socio-ecological factors, offering insights for policies to enhance C sequestration in AF systems. Policies frameworks and extension work should promote the importance AF practices, particularly HSD-AF, as effective strategies for C sequestration and climate change mitigation in Ethiopia.