Patterns in clonal traits in semi-dry calcareous grasslands in Slovenia

Due to the widespread importance of clonality in plants, investigating the mechanisms by which clonality-related traits are associated with community organization is crucial for a functional understanding of vegetation. In this study, the patterns in clonality and other life-history traits in a series of species-rich semi-dry grasslands (alliance Bromion erecti, order Brometalia erecti, class Festuco-Brometea) in the central-European region of Slovenia, all assigned to the same EUNIS (Middle European Bromus erectus semi-dry grasslands, code R1A32) and Natura 2000 habitat type [Semi-natural dry grasslands and scrubland facies on calcareous substrates (Festuco-Brometalia), code 6210 (important orchid sites)] were studied. The aims of this research were (i) to assess the diversity of clonal growth organs (CGOs) and other clonal traits in semi-dry grasslands and (ii) determine differences in distribution of clonal growth organs and other clonal traits in three plant communities (associations). Data from 224 vegetation plots (phytosociological relevés) with 247 species and nine plant traits of grassland species were used. This revealed that more than half of the plant species were clonal. Most common clonal growth organs (CGOs) were perennial splitting main root (produced by non-clonal plants), epigeogenous rhizomes and hypogeogenous rhizomes. For each plot, the community weighted mean (CWM) of all plant traits was calculated to determine differences between the three grassland types. Soil moisture and productivity seem to be the key factors associated with differences in clonal growth in the associations studied. Clonal tussock plants with rhizomes, and species with a rich bud bank and a high number of clonal offspring were abundant in grasslands with deep soils and mesic conditions (Onobrychido-Brometum association). Grasslands on stony soils over fissured limestone or dolomite and with more xeric conditions were characterized by rosette clonal plants with hypogeogenous rhizomes (Bromo-Danthonietum calycinae) and/or non-clonal plants with splitting main root (Scabioso hladnikianae-Caricetum humilis). The diversity and characteristics of clonality-related traits indicate that clonal growth is an essential feature of these species-rich grasslands. Importantly, the results of this study indicate that in order to support the characteristic species and functional composition of all types of grassland, management plans for semi-dry grassland habitats in the area studied need to be carried out at a finer scale (e.g. at the level of associations) than the level of EUNIS and Natura 2000 habitat types.