Restoration of grasslands on ex-arable land using regional and commercial seed mixtures and spontaneous succession: Successional trajectories and changes in species richness

Dry grasslands in the Protected Landscape Area and Biosphere Reserve of the White Carpathian Mts. in the eastern part of the Czech Republic, central Europe, belong to the species richest plant communities (on a scale of a few m2) in the world. Many of the grasslands were converted to arable land in the second half of the 20th century, but in the past two decades many of the arable fields have been re-grassed, most of them using commercial low-diversity clover-grass seed mixtures, some of them however by spontaneous succession or using a regional species-rich seed mixture. We asked how grasslands restored in various ways differ in their successional trajectories towards long-existing grasslands as reference sites, particularly in species richness and participation of target species. Altogether 35 grasslands restored with a regional seed mixture, 31 restored with commercial seed mixtures, and 16 restored by means of spontaneous succession were compared based on vegetation records (species cover in 5 m × 5 m plots). The data were processed using multivariate statistics. Grasslands restored in the three different ways converged in their species composition and developed generally towards reference grasslands. Considering the number of target grassland species, sowing of regional seed mixtures was the most successful, especially in the beginning, but processes of spontaneous succession led virtually to the same number of target species, even at sites re-grassed with commercial seed mixtures, but more slowly. Development of sites re-grassed spontaneously and by sowing commercial seed mixtures led to the establishment of more mesic vegetation (Arrhenatherion) than when using the regional seed mixture, which was predominantly composed of species typical of dry grasslands (Bromion). Thus, restoration of the most valuable dry grasslands should preferably be based on using properly designed regional seed mixtures.