Nature-based solutions for erosion mitigation : insights from a systematic review for the Andean region

The Andes Mountains stretch over about 8900 km and cross tropical, subtropical, temperate and arid latitudes. More than 85 million people lived in the Andean region by 2020, with the northern Andes being one of the most densely populated mountain regions in the world. The demographic growth and a stagnating agricultural productivity per hectare led to an expansion of the total agricultural land area, either upward to steep hillsides at high elevations covered by native grassland-wetlands ecosystems, or downward to lands east and west of the Andes covered by tropical and subtropical forests. Land use and management have significantly altered the magnitude and frequency of erosion events. 

This study systematically reviews the state of evidence on the effectiveness of interventions to mitigate soil erosion by water and is based on Andean case studies published in gray and peer-reviewed literature. After screening 1798 records, 118 empirical studies were eligible and included in the quantitative analysis on soil quality and soil erosion. Six indicators were pertinent to study the effectiveness of natural infrastructure: soil organic carbon and bulk density of the topsoil, soil loss rate and run-off coefficient at the plot scale, and specific sediment yield and catchment-wide run-off coefficient at the catchment scale. The protection and conservation of natural vegetation has the strongest effect on soil quality, with 3.01 ± 0.893 times higher soil organic carbon content in the topsoil compared to control sites. Soil quality improvements are significant but lower for forestation and soil and water conserva- tion measures. Soil and water conservation measures reduce soil erosion to 62.1 % ± 9.2 %, even though erosion mitigation is highest when natural vegetation is maintained.

Further research is needed to evaluate whether the reported effectiveness holds during extreme events related to, for example, El Niño–Southern Oscillation.