Integrated assessment of grassland restoration methods across Germany: Direct harvesting and regional seed mixtures are most successful for vegetation outcomes

Restoring species-rich grasslands is one of the key tools to bend the biodiversity curve. However, so far there have been few landscape-scale assessments of restoration methods as applied by practitioners across many sites, soil conditions, and regions. To improve the effectiveness of grassland restoration, broad-scale standardised assessments are needed that incorporate both positive and negative references, and evaluate total plant diversity as well as characteristic grassland species. The study assessed vascular plant diversity in 121 restored grasslands that cover different restoration methods, land-use legacies, restoration ages, and soil moisture levels across three regions in Germany. The results are compared with 33 positive (species-rich) and 33 negative (degraded) reference sites. We analysed diversity indices (total and characteristic plant species richness, total and characteristic Hill–Shannon diversity), the Favourable Conservation Status index (FCS_i), and the forb-graminoid ratio to assess the drivers and effects of restoration. Restoration improved the diversity of vascular plant species compared with negative reference sites, and some restored grasslands reached the diversity and FCS_i levels of positive references. Active (re)introduction of species, such as direct harvesting methods and regional seed mixtures, was most successful in enhancing plant species diversity towards the target communities, while cultivar seed mixtures and management adaptation were less effective. Neither the previous land use nor the restoration age significantly affected the restoration outcome in terms of species richness and species composition. Synthesis and applications. Direct harvesting and regional seed mixtures are the most effective methods to restore biodiverse and characteristic grassland plant communities. They outperform other methods regardless of land-use history and restoration age. This has positive implications for restoration of temperate grasslands in Central Europe, since land-use history is not a significant driver of restoration success, allowing the effective restoration on ex-arable land as well as on degraded grassland sites. Further studies should investigate the effects of combining direct harvesting and regional seed mixture sowing.