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

Two distinct species-rich dry grasslands differing in a number of synmorpho logical and syndynamical characters were studied for variance in species ri chness (VSR) and for guild proportionality (VGP). Guild proportionality was approached through the concept of deviation of variance of species richnes s within guilds as a departure from a null model. There was an excess of VS R at the majority of scales in both communities. In the Poo-Festucetum this excess is indicative of considerable heterogeneity of the studied stand. B oth 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 hi gher 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 pa llens, Thymus praecox, Hieracium bauhinii, Tortella inclinata and other sho wing high VGP form the matrix phase of the Poo-Festucetum. The gap explorat ors including spring ephemerals and non-clonal perennials are representativ e of guilds showing lower VGP than predicted by a null model. We hypothesiz e that vegetation patchiness caused by environmental heterogeneity and spat ially limited dispersal of the non-clonal species appear to be a more plaus ible explanation for the patterns of VSR and VGP rather than the competitiv e exclusion would be.