The dynamics of the population of a steppe perennial Senecio macrophyllus M.BIEB. during xerothermic grassland overgrowing

The study aimed to determine the long-term changes of the Senecio macrophyllus M.BIEB. population traits: the abundance, reproduction mode, individual fecundity, seed rain and recruitment of new genets in the course of xerothermic grassland overgrowing. The study had also the applied goal: to estimate the chances of "special care" species to survive in the changing environment without management regime for the maintenance of grassland. The model object was the island population of large-leaved ragwort on Biała Góra (the White Mountain) near Tomaszów Lubelski, South-East Poland. To achieve these aims I used the following sets of data: phytosociological relev,s made in plant communities in an interval of 16-18 years; repeated elaboration of the numbers and life-stage structure of the population, both by non-surface and surface method; observation of plants, life cycle in 50 labelled genets; population reproduction and seed rain amounts. The area of an open xerothermic grassland decreased due to the process of overgrowing by bushes which was accompanied by the increasing coverage of forest and meadow herbs as well as monocotyledons, mainly Brachypodium pinnatum and Calamagrostis epigejos. The abundance of the S. macrophyllus population noticable diminished. The flowering mode has been changing during years from an oscillation to a chaotic type which caused the significant decreasing of the individual fecundity, population reproduction and seed rain. In last years it was reflected in the interruption of juveniles’ recruitment.