B. Papp szerk.: Studia Botanica Hungarica 33. 2002 (Budapest, 2002)

Dobolyi, Konstantin: Studies of vegetation dynamics on the rock grasslands in Csíki-hegyek (Budaörs, Hungary)

marked on the field in such a way that they could be found and re-investigated any time in the future. The changes of vegetation were analysed and reported for the Authority of the Duna-Ipoly National Park after five years in 2001 (DOBOLYI 2001). MATERIAL AND METHODS Sampling was carried out so that visibly undisturbed open rock grasslands and dolomite slope steppes be represented. The relevés were taken from 2 m x 2 m quadrates. The cover values of the species were transformed to the scale 1 to 9 (MAAREL 1979). The scientific names of the species were taken from HORVÁTH et al. (1995). In 2001 the phytosociological relevés were repeated on the same places and with the same method as the one applied in 1996. The evaluation of the four investigated sites was based on the following species characteristics: phytogeographical area (floral element, HORVÁTH et al. 1995), phytosociological character, social behaviour type, degree of naturalness and indicator value of the nitrogen preference (BORHIDI 1993). The values of features characterising the sites have been calculated according to percentage pro rata of plant mass, that is the sum of the transformed cover values concerning one feature has been expressed in percentage of sum of all cover values of all species. The average naturalness value of the sites was calculated with the following formula: where NV = average naturalness value of the site; NV = naturalness value of the species (BORHIDI 1993); M = cover value of the species (MAAREL 1979); ^M = summarising according to the relevés (sum of the cover values of one species); ^ = summarising according to the species; ZM = sum of total cover values of the site. RESULTS The cover values and the additional data of the relevés are given in Tables 1 to 5. The floral composition and dominance of the species changed in a small degree in the interval between 1996 and 2001. Part of the changes can be explained by random processes (natural fluctuation), and partly by degradation. The fact and the tendencies of the degradation processes can be established and analysed by the statistical evaluation of the relevés.