The role of grassland for erosion and flood mitigation in Europe: A meta-analysis

Permanent grasslands are widely recognized for their role in protecting the landscape against soil erosion and flooding. However, this role has not yet been comprehensively quantified. Also, the degradation of grasslands is accelerating at an alarming pace, leading to erosion and runoff generation. This study aims to (i) quantify the erosion and flooding mitigation effect of permanent grasslands in the EU and the UK, compared to other land uses; (ii) review all soil erosion and runoff generating processes on permanent grasslands. First, a meta-analysis compared four erosion and flooding-related indicators: bulk density, hydraulic conductivity, runoff and soil loss between permanent grasslands, arable land and forests. The results show that permanent grassland soils had generally lower bulk density and higher hydraulic conductivity than arable soils, and generated less runoff and soil loss. Differences are less clear-cut in comparison with forests, although permanent grasslands had higher bulk density and runoff values. Secondly, a qualitative, in-depth review was performed to identify knowledge gaps related to the characteristics, importance and driving factors behind relevant soil erosion processes affecting grasslands in the EU. This identified six processes with appreciable knowledge gaps: trampling-induced erosion, gullying, piping, landsliding, snowmelt erosion, and avalanche erosion. Additionally, three processes were identified that promote runoff generation and soil erosion: compaction, hydrophobicity and wildfires.