Means and standard errors of selected plant community parameters calculated for the C (control) and I (invasion) plots within the Y (yellow dune) and G (grey dune) sites. As a significant site type × plot type interaction effect was found for all variables (Table 3; Suppl. material 1: table S3), the differences between plot types were examined separately for the two types of sites (using Tukey’s test) and marked with asterisks (*** p < 0.001, ** p < 0.01, * p < 0.05).