The aim of the yearly sampling of “Compositional Diversity Transects” (FH-CDT) at the Fülöpháza LTER site is to study the effects of weather on the spatial organization of open sand grasslands. Two open sand grassland patches have been sampled yearly from 2004 at the time of the phenological optimum of the communities. We collect data about the co-occurrence of vascular and non-vascular plant species in transects of contiguously arranged micro-quadrats. Transects are permanently marked. Plant presence is considered if there is an overlap between the aboveground part of a plant individual and the sampling unit (micro-quadrat). We sample 5 cm x 5 cm contiguous micro-quadrats arranged along 52 m long transects. One transect sampled in each patch. From the base-line data we estimate Compositional Diversity (i.e. diversity of species combinations), the number of realized species combinations, mean species richness and the spatial variance of species richness at three representative scales (5 cm x 5 cm; 5 cm x 25 cm; 5 cm x 200 cm) using computerized sampling.