Impacts of indigenous agroforestry practices and elevation gradient on ecosystem carbon stocks in smallholdings’ farming system in South-Central Ethiopia

Abstract

Agroforestry systems have been recognized for their high carbon (C) capture but vary across agroforestry practices and elevation gradients. Four distinct traditional agroforestry practices namely, dispersed trees in perennial crops, homesteads, boundary plantations, and woodlots, under smallholdings along elevation gradients were assessed. Using stratified random sampling, 540 sample quadrats in three elevations were randomly selected for biomass carbon stocks accounting. In addition, 180 sample quadrats were randomly selected for litters, fine roots, and soil organic carbon assessment. Litters and fine roots carbon stocks were determined based on loss-on-ignition and soil organic carbon (0–30 cm and 30–60 cm) determined using Walkley–Black method. The mean (± sd) biomass carbon stock in the boundary plantation was significantly (p < 0.001) higher by 64, 80, and 91% than woodlots, dispersed trees in perennial crops, and homesteads, respectively. The mean (± sd) ecosystem carbon stock (in biomass, litters, fine roots, and soil) in boundary plantation was significantly (p < 0.001) higher by 71, 64, and 47% than homesteads, dispersed trees, and woodlots, respectively. Litters and fine roots biomass carbon stocks showed insignificant contributions to ecosystem carbon stocks, valued 0.4 and 1.9%, respectively. Ecosystem carbon stock was significantly (p < 0.001) higher at the upper and middle elevations than the lower elevation. Observation on the interactions between elevation gradients and agroforestry practices did not show significant effect. Future attempts in agroforestry designs for tree intensifications and enhanced ecosystem carbon stocks should take into account the various distinct agroforestry practices and elevation gradients.