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Csiky J., Onyshchenko V. & Chytrý M. (2020) Oak-hornbeam forests in central Europe: a formalized classification and syntaxonomic revision. -Preslia 92: 1-34Oak-hornbeam forests (order Carpinetalia) are a widespread vegetation type in central Europe. As vegetation ecologists focused on them since the pioneering times of vegetation research, many syntaxonomic units are described. However, classification systems used in various central-European countries suffer from inconsistencies and overlaps of the concepts of particular associations. Currently there is no consistent syntaxonomic system based on numerical analysis of vegetation plots that would be valid for the whole of central Europe. Therefore, the main goal of this study is to provide a revised syntaxonomic system of oak-hornbeam forests across central Europe, develop formal definitions of the associations and include these definitions in a classification expert system. We recognized 13 associations, 9 from the alliance Carpinion betuli (central-European oakhornbeam forests) and four from the alliance Erythronio-Carpinion (Illyrian and northern Italian oak-hornbeam forests). We prepared an expert system that classified 55% of the relevés in a central-European oak-hornbeam forest dataset (n = 6212) at the association level. To stabilize the Carpinion betuli association names, we selected nomenclatural type relevés for associations that have not been typified so far. In addition, two association names (Poo chaixii-Carpinetum and Pseudostellario-Carpinetum) were validated. Ordination revealed the main drivers of species diversity in these forests, including a complex gradient of soil moisture, nutrient availability and geographical position (mainly latitude). Among the climate variables, annual temperature amplitude and mean annual temperature were most closely correlated with species composition. K e y w o r d s: Carpinetalia betuli, Carpinion betuli, classification expert system, Erythronio-Carpinion, formalized vegetation classification, syntaxonomy, temperate broad-leaved deciduous forests

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-Galium divaricatum Pourr. ex Lam. is an annual plant species occurring mainly on dry grasslands. The centre of its distribution range is situated in the Mediterranean region, while in Central Europe it has been known only from a few isolated sites in Slovakia and Hungary. In 2016 we discovered this species in open dry grassland of the class SedoScleranthetea on the upper edge of a basaltic andesite quarry near the village of Siltse, Irshavskyi District, Zakarpatska Region, as a new species for the Ukrainian flora. The site is situated in the transitional region between the Pannonian Basin and the Eastern Carpathians. The new locality represents the northernmost recent occurrence of this species.

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We studied the diversity of calcicolous rock-outcrop forest vegetation dominated by lime (Tilia cordata, T. platyphyllos and T. tomentosa) in northern Austria, the Czech Republic, southern Poland, Slovakia, northern Hungary and northwestern Romania. This vegetation includes species-rich forests with a mixture of mesophilous and thermophilous forest species, dry grassland species and species of rock outcrops. It is classified in the alliance Melico-Tilion platyphylli of the order Aceretalia pseudoplatani (class Carpino-Fagetea). It is rare in the study area, usually occurring on the upper parts of steep rocky slopes with shallow soil on limestone or other types of base-rich bedrock. Since such conditions are unfavourable for the development of closed-canopy zonal forests, numerous light-demanding relict species occur there (e.g. Dianthus praecox, D. spiculifolius, Primula auricula, Sesleria spp., Tephroseris integrifolia and Viola jooi). Based on the results of unsupervised classification using original (n = 118), previously published (n = 87) and unpublished relevés stored in the EVA database (n = 6; thus 211 relevés in total), we distinguished three phytosociological associations: (i) Tilio platyphylli-Fraxinetum excelsioris occurring in central Slovakia and northern Hungary, (ii) Spiraeo chamaedryfoliae-Tilietum cordatae, a new association recorded in northern and western Romania, and (iii) Seslerio caeruleae-Tilietum cordatae occurring in the Czech Republic, northern Austria, northern Hungary, western Slovakia and also in southern Poland, where we recorded this community for the first time in this country. We created an expert system for automatic classification of these forests, which includes formal definitions of the three associations and seven subassociations.