Variance in species richness and guild proportionality in two contrasting dry grassland communities

Two distinct species-rich dry grasslands differing in a number of synmorphological and syndynamical characters were studied for variance in species richness (VSR) and for guild proportionality (VGP). Guild proportionality was approached through the concept of deviation of variance of species richness within guilds as a departure from a null model. There was an excess of VSR at the majority of scales in both communities. In the Poo-Festucetum this excess is indicative of considerable heterogeneity of the studied stand. Both excess and deficit of VGP than predicted by a null model (Site Model by J. B. WILSON:) were found in the studied grasslands. The guilds showing higher VGP than predicted by a null model are represented by the three major dominant taxa (Sesleria albicans, Genista pilosa, Hypnum cupressiforme var. lacunosum) in the Carici-Seslerietum, The clonal plants such as Festuca pallens, Thymus praecox, Hieracium bauhinii, Tortella inclinata and other showing high VGP form the matrix phase of the Poo-Festucetum. The gap explorators including spring ephemerals and non-clonal perennials are representative of guilds showing lower VGP than predicted by a null model. We hypothesize that vegetation patchiness caused by environmental heterogeneity and spatially limited dispersal of the non-clonal species appear to be a more plausible explanation for the patterns of VSR and VGP rather than the competitive exclusion would be.