Soil transfer impacts restored soil profiles and hydrodynamic properties

Natural and semi-natural grasslands, particularly dry grasslands, are high-value biodiversity hotspots in Europe and major challenges for ecological conservation and restoration. Soil transfer has been used successfully to restore dry grassland ecosystems (soil and vegetation), but should only be applied as a last resort and where an undegraded ecosystem has previously independently been earmarked for destruction. Assessing overall restoration success means taking soil recovery into account as well as vegetation regener-ation. In Mediterranean regions and under global warming, soil hydrodynamic properties are the most critical limiting factors for the restoration of dry ecosystems. This study analyses soil physico-chemical parameters and hydrodynamic properties in reconstructed soils after soil transfer following a petrol land spill. Six years after soil transfer and compared to the surrounding soil reference steppe, the horizons of the soil transfer treatments were significantly less colonised by plant roots and showed very few biological activities and earthworm galleries. Then, their porosity was also significantly lower. Hydrodynamic properties continue to differ significantly be-tween the restored site and the surrounding reference steppe ecosystem. There is also less available soil water and water drains faster in all soil transfer treatments. This can be explained by significant higher finer grain size (clays, silt), chemical elements (N, P, K), and plant cover for soil transfer treatments but significant, lower levels of organic matterdue to mechanical soil compaction during soil spreading. The soil transfer treatment involving full reconstitution of the three main soil layers yields the most encouraging results. However, the question arises of whether long-term vegetation recovery might be compromised by soil hydrological dysfunction under global warming.