Grassland restoration by local seed mixtures: New evidence from a practical 15-year restoration study

Aim: Local seed mixtures are frequently used to restore species-rich grasslands. However, it has hardly been tested whether local seed mixtures can actually be applied successfully in grassland restoration practice at larger scales and long-term. To close this gap, we report the results of a large-scale restoration study in which grasslands were restored about 15 years ago using different local seed mixtures. Location: Bavaria, SE Germany. Methods: To evaluate the efficacy of the local seed mixtures, we compared the species composition of seed mixtures and current vegetation. We then tested whether restoration success depends on site characteristics such as the size and shape (rectangle or stripe) of the grassland, restoration procedures such as topsoil removal, seed density and land use, or species habitat preferences for light, water and nutrients, and species life span (annual, perennial). Results: On average, the current vegetation contained 62.4% of all species that were present in the local seed mixtures. Species from the local seed mixtures made up on average 69.1% of the total cover in the established vegetation, whereby the species composition of the local seed mixture and vegetation differed significantly from each other. The probability that a sown species would establish increased with seed density up to 300 seeds/m². Furthermore, habitat preferences significantly affected species establishment chances, with species requiring full illumination, dry and nutrient-poor soil being more successful during restoration, reflecting the high proportion of sites with topsoil removal prior to seeding in our study. Annual species had significantly lower establishment chances compared with their perennial counterparts. Conclusions: Our study provides another piece of evidence that local seed mixtures can be applied successfully in large-scale grassland restoration projects. We provide several practical recommendations of how such practices can be further improved by using specific seed densities and creating new local seed mixtures using species that are ecologically more suitable to the restored sites.