Does topsoil removal in grassland restoration benefit both soil nematode and plant communities?
Successful restoration of semi-natural grasslands on grasslands previously subject to intensive management needs to overcome manifold barriers. These include high soil fertility, the dominance of a few fast-growing plant species, degraded soil faunal communities and missing propagules of the targeted above- and below-ground flora and fauna. A combination of removing the topsoil and introducing propagules of target plants has become one of the major tools for nature conservation agencies and practitioners to reduce soil fertility and restore former species-rich grasslands in various European countries. Using topsoil removal as a restoration measure has provoked an ongoing debate between supporting nature conservation and rejecting soil protection agencies. Although it favours species-rich plant communities, it strongly disturbs soil communities and affects physical and chemical soil properties and processes. Currently, there is a lack of long-term data to assess how restored grassland ecosystems develop and recover after topsoil removal. Here, we used two well-established bioindicators, soil nematodes and plants, to quantify restoration success of topsoil removal in comparison with alternative restoration measures and target communities 22 years after intervention. The nematode community composition indicated reduced nutrient availability in the restored systems, as was aimed at by topsoil removal. Nevertheless, after this 22-year period following topsoil removal, nematode composition and structure revealed successful recovery. Plant communities benefitted from the reduction of soil nutrients after topsoil removal as indicated by higher numbers of plant species and higher Shannon diversity. Furthermore, topsoil removal strongly promoted the re-establishment of plant species of the target plant community. Synthesis and applications. Overall, our study demonstrates how a massive intervention by topsoil removal proved successful in converting intensively managed into species-rich grasslands. This contrasts with the mild intervention of repeated mowing and removing of the harvested plant material. We show that, in the long run, potential negative effects of topsoil removal on the soil fauna can be successfully overcome and plant communities can develop into targeted species-rich grassland.