The Stipo-Poion puzzle: syntaxonomic revision of the dry and semi-dry grasslands of the Eastern Alps

We present a revised classification of the dry and semi-dry grasslands of the Eastern Alps, based on a data set of 2924 relevés. We used TWINSPAN to analyse the floristic patterns and translated the result into a syntaxonomic system. At the highest level, xeric grasslands (i.e., rocky steppes and grass steppes) were separated from meso-xeric (i.e., semi-dry) grasslands. Within the first group, a strong biogeographical gradient was revealed, separating the dry grasslands of Tyrol and adjacent regions from those further east. Most of the xeric grasslands are rocky steppes while grass steppes are very rare in the Eastern Alps and were only separated at a low hierarchical level within the two geographical subgroups. Our findings suggest that the diagnostic species of the orders Festucetalia valesiacae and Stipo-Festucetalia pallentis as determined in previous studies for east-Central and Eastern Europe are not directly applicable to the inner Alps. Thus, for the time being, we refrain from separating rocky steppes and grass steppes at the order level and unite them in a single order Festucetalia valesiacae (s.l.) with three alliances: Stipo-Poion xerophilae (steppic grasslands of Tyrol and adjacent regions; incl. Diplachnion serotinae), Seslerio-Festucion pallentis (rocky steppes of Eastern Carinthia, Styria and Lower Austria) and Festucion valesiacae (grass steppes of Lower Austria). The semi-dry grasslands are included in the order Brachypodietalia pinnati with two alliances: Mesobromion (northern margin of the Alps between Vorarlberg and Salzburg) and Cirsio-Brachypodion (inner and easternmost Alps). In terms of associations, we distinguish 12 in the Stipo-Poion xerophilae, 7 in the Seslerio-Festucion pallentis, 3 in the Festucion valesiacae, 5 in the Cirsio-Brachypodion and 3 in the Mesobromion. Finally, we discuss the assignment of these syntaxa to EU habitat types.