Evaluating the impact of assisted natural regeneration and afforestation on soil erosion dynamics using high-resolution imagery in semi-arid Ethiopia
In 2015, trees covered just 1.9% of these Ethiopian drylands; nine years later, helping old roots regrow pushed forest cover above 22%.A comprehensive study evaluating land restoration in the Kembata Tembaro district of central Ethiopia shows that protecting wild growth and planting new trees have significantly reduced severe topsoil loss across dry, hilly areas.The research was published in the scientific journal Scientific Reports by lead author Melese Wondatir Sisay. The investigation evaluated the real-world impact of the REDD+ Investment Program, an environmental initiative launched in 2015 with funding support from the Norwegian government. By examining high-detail satellite images provided by Norway’s International Climate and Forests Initiative alongside ground height maps and historical rainfall records, the research team mapped land changes and soil movement between 2015 and 2024 across six pilot test sites covering over 107 square kilometres.Three test sites were restored using assisted natural regeneration, a management strategy that focuses on protecting existing root systems and managing surrounding land so native bushes and trees can regrow naturally without expensive nursery planting. At these locations, forest cover grew from 1.9% in 2015 to 22.18% in 2024. As a result, annual soil loss dropped from 13.19 tonnes per hectare down to 9.49 tonnes per hectare over the nine-year evaluation period.
Tree planting drives steep drops in topsoil loss
Direct tree-planting programs delivered even larger increases in forest canopy alongside major reductions in washing-away topsoil. Across three tree-planting pilot sites where new saplings were actively added to bare or deforested land, forest cover expanded from 8.5% in 2015 to 34.92% by 2024.Because these active planting sites suffered from extreme land damage when the project began, initial topsoil loss was extremely high, standing at 43.37 tonnes per hectare per year in 2015. By 2024, protective tree cover helped lower that loss to 31.29 tonnes per hectare per year.The findings provide crucial data for Ethiopia’s National Forest Development Strategy and its Climate Resilient Green Economy policy frameworks. In the country’s dry highlands, rapid population growth, unpredictable rainfall, and heavy farming frequently cause steep slopes to lose anywhere from 20 to 100 tonnes of topsoil per hectare every year. This continuous erosion washes away nutrient-rich earth, directly weakening farm yields, damaging agricultural productivity, and threatening food supplies for local communities.
Satellite tracking reveals landscape recovery
To track these environmental changes accurately over time, the researchers analyzed sharp 4.77-metre resolution satellite photos inside Google’s cloud-based mapping software. They categorized the regional landscape into seven basic cover types: dense forest, open forest, brushland, farmland, grassland, bare dirt, and towns.The satellite mapping proved highly reliable when checked against 356 real-world ground locations verified through detailed aerial photos. The mapping achieved an overall accuracy of 81.4% for the 2015 baseline data and reached 86.79% accuracy for the 2024 map.To estimate how much dirt was actually saved from erosion, the researchers built a computer formula that combined long-term rainfall averages from 1990 to 2024, local ground slopes, soil types, and plant cover. Known as the Revised Universal Soil Loss Equation model, this standard calculation estimates how different weather and ground factors work together to cause or prevent land washing away. When tested using standard statistical reliability checks, the model demonstrated strong predicting power, scoring 0.823 out of a maximum score of 1.0.
Local geography and climate conditions
The local geography of the Kembata Tembaro district features a varied terrain of high flatlands, deep valleys, and rolling hills, with heights ranging from 800 metres to 2,600 metres above sea level. This wide height range creates distinct local weather zones. However, nearly all the test zones (95%) sit within the hot, dry lowlands known locally as the Kola zone, located below 1,500 metres in altitude, with smaller sections extending into mid-altitude hills known as Weyna Dega.The REDD+ Investment Program has established large-scale community forestry programs across 54 districts in Ethiopia, covering four major administrative regions including Amhara, Central Ethiopia, Sidama, and Oromia. The Kembata Tembaro district was selected for this study through targeted sampling to reflect a realistic range of physical slope conditions and land types across the region.
Guiding future forest restoration strategies
While planting new nursery seedlings remains necessary on completely bare ground, protecting living root systems and allowing native trees to sprout on their own offers a lower-cost, highly effective way to heal damaged communal land.The research team notes that these findings provide clear real-world proof that combining natural regrowing methods with active tree planting can successfully protect farmland, stop topsoil loss, and rebuild resilient forests across dry regions facing severe environmental pressures. Go to Source
