To evaluate the relative roles of seed availability and competitive,interactions in creating within-community patterns of species richness in unproductive grassland, we conducted a sowing experiment in a dry calcareous (alvar) grassland, where both the number of arriving seeds and the number,of arriving species were,approximately,doubled,compared to the natural seed rain. Also, in half of the plots, 36% of the vegetation and bryophyte cover was removed,to simulate,disturbance. Sowing significantly increased,species richness and,the number,of seedlings,in plots. Disturbance,increased,the number,of seedlings,but had no significant effect on species richness. In the first year, the highest number of seedlings was,found in disturbed and sown,plots. The dynamics,of seedling numbers,differed among species. Of the 15 sown species, seedlings of nine species were found in some plots. The number of seedlings of two species were not dependent on treatments, those of three species depended only on sowing, and for four species there was a significant positive interaction between,sowing,and disturbance. The establishment,of sown,species was,not dependent,on initial species richness or number,of adult ramets,in experimental,plots. It was,concluded that, though the behavior of individual species may differ, the local deficiency of seeds may,be an important,force generating,small-scale community,patterns of calcareous,grass- lands. Key words:,alvar grassland; calcareous grassland; community,pattern; disturbance; dynamic equilibrium; gap; perennial grassland; seed limitation; seedlings; species richness.