Restoring plant and pollinator diversity in lowland grasslands using different seed addition methods

The biodiversity of semi-natural grasslands has dramatically declined over the past century, largely due to the intensification of management practices. In this study we experimentally tested the efficacy of different assisted (active) restoration methods to increase plant and invertebrate biodiversity in relatively species-poor extensively managed Swiss lowland meadows. Four restoration treatments and a control were randomly established in 2019: 1) hay transfer from a species-rich donor meadow to a harrowed receiver meadow; 2) the same as 1), but to a ploughed meadow; 3) sowing a directly harvested native seed mixture originating from a species-rich donor meadow to a ploughed meadow; 4) sowing a propagated native mixture on a ploughed meadow; 5) control, with no soil disturbance and no reseeding. The experiment was conducted at field scale and replicated 12 times across the Swiss Plateau. Vegetation surveys were performed before (2018) and after the restoration (2021–2024). Pollinators were sampled in 2022 (wild bees and hoverflies) and 2024 (butterflies). After a marked increase in 2021, plant species richness stabilised in 2023 in most treatments with on average 29% more species compared to 2018 and 16% more species in restored compared to control meadows in 2023. Regional differences (beta diversity) were more pronounced in the hay transfer treatments. Harrowing before sowing proved to be as effective as ploughing. Importantly, in 2023, 90% of the restored meadows qualified for the result-based payment scheme, whereas none qualified before restoration. Wild bees and butterflies responded positively to the restoration treatments, though not consistently across all treatments. Hoverflies, as well as other invertebrate groups, showed no response. This real-scale study provides evidence-based recommendations for restoring grasslands through practical and financially viable methods. The results-based payment scheme acts as a strong legislative incentive, encouraging farmers to implement management measures that deliver higher biodiversity outcomes and, in turn, secure higher financial income.