1. Spatio-temporal dynamics of biodiversity are a key measure when monitoring restoration success. Balanced species turnover is aimed at because it increases overall biodiversity and improves ecosystem stability and multifunctionality. For predictive restoration, it is important to analyse spatial beta diversity and to identify its drivers like site characteristics but also uncontrolled factors like spatial effects, historical factors, year effects and non-directional temporal turnover.2. We studied dike grasslands 4–19 years after restoration at River Danube in SE Germany over five years (2017–2021, 41 plots in 12 sites). We calculated beta diversity indices to describe spatial variation and temporal turnover, including their additive components ‘replacement’ and ‘nestedness’, or ‘gains’ and ‘losses’.3. The analysis of the spatial variation of the restored dike grasslands did not reveal homogenisation despite a significant temporal turnover, and was largely dominated by replacement-driven dissimilarity. The replacement drivers changed over time, although replacement was mainly affected by exposition and spatial factors. Historical factors were inconsistent over time, and no statistically clear drivers were found for nestedness.4. The dike grasslands exhibited on average 37 ± 11% (mean ± SD) year-to-year turnover in species composition, with some spatio-temporal variation. Gains and losses were balanced over time, although prevalences changed over time and were most pronounced on south-exposed slopes.5. The restored grasslands exhibited spatial variation by site characteristics but also uncontrolled spatial factors. Moreover, high non-directional temporal turnover caused by weather fluctuations, slightly varying management, and stochastic biotic dynamics influenced spatial variation. Thus, restoration targets should be defined as a desired variation of alternative states. Furthermore, the dominance of replacement should move the focus from searching the perfect fit for certain targets to a variation of the approaches to increase beta diversity.

Sowing is a well-established restoration technique to overcome dispersal limitation. Site-specific seed mixtures are most effective to achieve functional communities. This is especially important if the restored vegetation has to protect critical infrastructure like roadsides and dikes. Here, an improved seed-substrate combination will secure slope stability, reduce mowing efforts, and generate species-rich grasslands. A factorial field experiment addressed this topic on a dike at River Danube in SE Germany in 2018-2021. Within 288 plots, we tested three sand admixtures, two substrate depths, two seed densities and two seed mixture types (mesic hay meadow, semi-dry calcareous grassland) in north and south exposition, and measured the recovery completeness by calculating the successional distance to reference sites, the persistence of sown species, and the Favourable Conservation Status (FCS) of target species. Overall, the sown vegetation developed in the desired direction, but a recovery debt remained after four years, and some plots still showed similarities to negative references from ruderal sites. In north exposition, hay meadow-seed mixtures developed closer to the respective reference communities than dry-grassland mixtures. In south exposition, the sown communities developed poorly which might be due to a severe drought during establishment. This initial negative effect remained over the entire observation period. Sand admixture had a slightly positive effect on target variables, while substrate depth, seed density and mixture type had no effects on species persistence or FCS. Synthesis and applications: Site-adapted seed mixtures make restoration more effective. However, applying several seed-substrate combinations might foster beta diversity. Furthermore, additional management efforts are recommended, as they might be necessary to reduce the recovery debt, as well as re-sowing after unfavourable conditions.