Chalk rocky grasslands in the arid Eastern European Plain

Chalk rocky grasslands of the arid Eastern European Plain are endangered and highly important for biodiversity protection. This study aimed to revise previous syntaxonomic concepts, compare chalk rocky grasslands with other calcareous rocky grasslands and provide a unified classification of chalk rocky grasslands. We extracted relevés from the European Vegetation Archive and added relevés from protologues and papers describing chalk rocky grasslands within the study area. We pre-selected an initial dataset of calcareous rocky grasslands, which we narrowed down to the class Stipo pulcherrimae- Festucetalia pallentis. These were further classified using a modified TWINSPAN algorithm. We classified them as Anabasio cretaceae-Agropyrion desertori, Sileno fruticulosae-Nanophytion erinacei, Anthemido trotzkianae-Artemision salsoloides, Sileno supinae-Artemision hololeucae, Euphorbio cretophilae-Thymion cretacei and transitional communities of the Centaureo carbonatae-Koelerion talievii alliances within two orders with validation of some syntaxa. The communities are clearly differ- entiated from each other along gradients of climate and edaphic properties. Differences to other Euro- pean limestome communities are given. We provide the first unified European classification of conti- nental chalk rocky grasslands, including Ukrainian, Russian and Kazakh communities.