The Restoration Debt Remains: Topsoil Removal and Different Mowing Regimes Reach Desired States of Calcareous Grassland but Do Not Match the Reference

Questions Restoring calcareous grasslands on former arable land can help to increase the area and connectivity of remnants. Long‐term restoration experiments with green hay transfer or topsoil removal on ex‐arable land can be combined with different mowing either in early summer or autumn. We investigated which of these treatment combinations achieves the highest efficacy, as measured by similarity to old‐growth reference grasslands. Location Nature reserve “Garchinger Heide” in southern Germany and restored calcareous grasslands in the surroundings. Methods Vegetation surveys were conducted in 62 old‐growth and 85 restored grassland plots. Furthermore, we added plots from former surveys of the old‐growth grassland. We assessed species richness, functional plant traits, species composition, and classified the plots into EUNIS habitat types. Topsoil was removed in 1993, 1996, and 2003 (30 plots). Since 2020, some sites had been mown in late summer (25 plots) or in autumn (30 plots). Results None of the restoration methods lead to a “carbon copy” of the reference grassland. Topsoil removal resulted in different outcomes compared to mowing, while mowing date had no effect. More than half of the plots on the restored sites could be classified as the target EUNIS habitat. Compared to the reference, mowing supported a higher number of lowland hay meadow species, while topsoil removal had not only fewer specialists of calcareous grasslands but also fewer non‐target species. At mowed sites without topsoil removal, the prevailing species had greater height and a larger specific leaf area compared to the respective species at reference sites. By comparison, species at sites with topsoil removal had a lower seed mass and specific leaf area. Conclusion Topsoil removal and mowing regimes produced different restoration outcomes in calcareous grassland, and neither reached the species composition of the old‐growth reference. This recovery gap emphasizes the limitations of calcareous grassland restoration and the need to prioritize conservation of old‐growth grassland remnants. However, most restored sites of any approach achieved the status of EUNIS habitat types, which is why different outcomes can be seen as a beneficial increase in spatial heterogeneity for plant diversity.