A novel dataset of permanent plots in extremely species-rich temperate grasslands

The extreme species richness of some temperate grasslands is a globally relevant yet understudied phenomenon. Until now, few records from thoroughly sampled, though not permanently fixed, vegetation plots were available. We therefore established a network of 40 permanent 4 × 4-m2 plots in species-rich grasslands of the White Carpathians (Czechia), Ukraine, Hungary and Romania. Thirty-one of them form the main dataset comprising plots from discrete forest-steppe grasslands (the Brachypodio-Molinietum association of the Cirsio-Brachypodion pinnati alliance), while nine of them forms the local dataset from a single locality in the White Carpathians, whose vegetation lacks most forest-steppe species and is transitional between the Bromion erecti and Arrhenatherion elatioris alliances (the Anthoxantho-Agrostietum and Anthyllido vulnerariae-Trifolietum montani associations). The permanent plots contain a nested subplot of 1 m2, except for five plots from Ukraine and Romania. Most plots harboured at least 80 vascular plant species per 16 m2, with the mean richness of 16-m2 plots was 95.3 species in the main dataset and 84 species in the local dataset. Mean richness of the 1-m2 subplots, presumably reflecting local environmental conditions and competitive relationships more than that of 16 m2 plots, did not vary between the two datasets, with a general mean of 57.6 species. Species counts of 16-m2 plots and 1-m2 subplots correlated, albeit only moderately, only in the main dataset. The presented datasets may be used for comparative analyses as well as for a future revisiting of the plots and may bring novel insights into the dynamics of extreme species richness.