Evaluating the impact of assisted natural regeneration and afforestation on soil erosion dynamics using high-resolution imagery in semi-arid Ethiopia

Abstract

Ethiopia's highlands face a serious degradation and soil erosion driven by unstable land use, climate variability, and rapid population growth. In response, the Reduced Emissions from Deforestation and Forest Degradation (REDD+) program has implemented various techniques, such as afforestation and assisted natural regeneration interventions in Ethiopia; however, the effectiveness of these practices has not been assessed yet. This study aimed to analyze the effects of afforestation and assisted natural regeneration practice on soil erosion dynamics, specifically in the Kembata Tembaro district. The study utilized high-resolution satellite imagery (4.77 m) from Norway's International Climate and Forests Initiative (NICFI), SRTM DEM (30 m resolution), and WorldClim. The land use and land cover change analysis was conducted in Google Earth Engine (GEE) utilizing a Random Forest (RF) classifier. In addition, the soil loss estimation was analyzed for six pilot sites (three afforestation and three-assisted natural regeneration) for two periods in 2015 and 2024 utilizing the Revised Universal Soil Loss Equation model, integrating rainfall erosivity, soil erodibility, cover management, soil management practices, and topographic impacts. The study revealed that the forest cover notably increased across both sites, increasing from 1.9% to 22.18% in the assisted natural regeneration and from 8.5% to 34.92% for afforestation and reforestation sample sites. Consequently, the 2015 annual soil loss, which was 13.19 t/ha/y, declined to 9.49 t/ha/y in 2024 over the three ANR sites. In addition, the 2015 estimated annual soil loss for all AR sites, 43.37 t/ha/y, declined to 31.29 t/ha/y in 2024. The accuracy of the RUSLE-based soil erosion model, as calculated by the ROC curve analysis, demonstrated strong predictive performance with an AUC of 0.823. The key finding of the study revealed that both interventions have a critical role in preserving forest cover, mitigating erosion, and enhancing ecosystem resilience. Overall, the study's findings provide evidence for scaling up interventions to achieve Ethiopia's climate-resilient green economy goals.