Long-term soil hydraulic recovery following topsoil removal in restored nature

Nature restoration projects often aim to improve biodiversity, while many soil-related ecosystem services like water retention, are often not accounted for and may negatively be affected by restoration measures. In the Netherlands, topsoil removal, or sod cutting, is commonly implemented in areas where agricultural fields are being transformed into heathlands to remove the nutrient-enriched topsoil. Heathland restoration is a key objective within the European Natura 2000 network. While this intervention effectively lowers soil fertility and promotes the establishment of the target heathland vegetation thereby fostering biodiversity, its long-term effects on soil hydraulic properties are not well understood. Given that soil water retention is a key soil property influencing catchment resilience to droughts and floods, assessing soil hydraulic change following restoration is necessary for evaluating restoration outcomes. 
This research investigates the change of soil water retention in restored heathlands within the Drents-Friese Wold national park, the Netherlands, located within the European Sand Belt. At each site, 30 to 50 cm of organic-rich topsoil was excavated, exposing underlying horizons with minimal pedogenic development. A chronosequence approach was applied at sites where topsoil removal occurred in approximately 1995, 2005, and 2020, representing up to three decades of soil development. Undisturbed soil samples were collected from each chronosequence stage; from an abandoned intact agricultural site, and from long-established heathland exceeding 200 years that represents the restoration target. Additionally, samples were collected from the subsoil at 40 cm depth beneath intact agricultural soil to separate the effects of topsoil removal from the original soil conditions at that depth. Soil water retention curves were determined for all samples using combined suction table and pressure plates, complemented by measurements of bulk density, organic matter content, and particle size distribution. 
Although topsoil removed sites achieve nutrient-poor conditions favorable to heathland species, visual soil observations suggest that the aggregated structure and biological pore networks present in the original agricultural topsoil did not recover  even after three decades. By quantifying recovery timescales and comparing hydraulic properties across restoration states, this research illustrates that rapid measures for nature restoration comprise long-term soil functioning, with implications for restoration practice across similar ecosystems.