Despite the large-scale human presence in cities, valuable natural habitat fragments survived, displaying outstanding biodiversity. In and around Budapest (Hungary), species-rich sandy grassland vegetation has shrunk drastically and has remained only in small patches and fragments. The presence of invasive plants is a serious problem in all protected sites of Budapest because they endanger the flora and fauna of the isolated habitats. At the Újpest Homoktövis Nature Conservation Area, conservation interventions have been taking place since 2006 to preserve the grassland fragments in the long term. We followed the effects of this management by surveying coenological relevés in ten permanent quadrats of 1× 1 m each in seven sample sites in 2012 and 2013. We evaluated the coenological records according to the relative ecological indicators (water and nitrogen) of the species. Detrended correspondence analysis (DCA) was also used for data analysis. Changes of the vegetation could be clearly observed during a 7-year-long period, because the species of the sandy grassland have become dominant and this was favourable regarding the aims of the nature conservation. In the stands where management had been carried out for 7 years, a natural or nearly natural vegetation developed, and invasive species and weeds disappeared.