Secondary succession and seed bank formation was studied in a formerly grazed, abandoned, eastern Hungarian sandy steppe-meadow (Pulsatillo-Festucetum). The vegetation was sampled at different elevations of a sand dune which became partly invaded by the tree Robinia pseudo-acacia ca. 10 yr ago. Pre-abandonment vegetation records were used as historic references. Though composition of the non-invaded grassland only changed moderately, dominance of tall grasses (Elymus hispidus, Poa angustifolia) increased significantly at the cost of annuals and low stature perennials. In the stand invaded by Robinia most grassland species were lost and replaced by nitrophytes. Vertical position influenced species abundance, but affected the composition only moderately. Fine-scale zonation of the vegetation also changed with time. Species richness of the above-ground vegetation and the seed density of soil samples at the lower elevation were slightly greater than at the higher sites.
Seed banks of sensitive grassland specialists (e.g. Pulsatilla pratensis subsp. hungarica) disappeared during grass encroachment. Following extinction from above-ground vegetation, restoration must rely on dispersal from adjacent areas. In contrast, several annuals and perennials, which survived this degradation stage in the above-ground vegetation, possessed seed banks. Many of these species became extinct from the vegetation during the Robinia invasion but left viable persistent seeds. This fact is promising for restoration of the Potentillo-Festucetum sandy pasture. Competitive weedy species and sprouting Robinia can, however, limit seedling establishment.
Abbreviations: BIC = Bayesian Information Criterium, NMDS = Non-metric Multidimensional Scaling.