Fig. 2

Relative response indexes (RRIs) calculated for total vegetation cover, species richness, target species cover and weed cover in the plots restored by topsoil removal (red boxes) and topsoil transfer (blue boxes) in the three studied years. Values of RRI range from − 1 to + 1. The closer the RRI is to zero, the higher the similarity of the restored vegetation to the target grasslands, whereas the closer |RRI| is to 1, the lower the similarity. Negative values indicate lower values in the restored than in the reference grasslands, and positive values indicate higher values in the restored than in the reference grasslands. Different superscript letters indicate significant differences between groups (p < 0.05, repeated measures general linear models and Tukey tests, N = 480). Boxes represent the interquartile region of value distribution (between 25% and 75% quartiles), the bold inner lines visualize the mean, vertical lines show the value range in the lower or upper quartile, respectively, and asterisks represent outliers (values that are lower or higher by 1.5× the interquartile range from the lower or upper quartile, respectively). Each boxplot represents data from 80 plots