Our paper presents the results of research conducted in the Mala River Valley located 22 km south of Warsaw, Poland. The study examines successional changes under different management regimes in natural meadow habitats included in the European Union’s Natura 2000 network. The meadow species composition, structure, and diversity in areas mown early, late, sporadically, and the unmown ones were examined. Changes in the natural habitat and woody vegetation areas were also analysed. The results showed a 40% reduction in natural habitat and a 57% increase in woody vegetation coverage over a six-year period, which indicates rapid and progressive succession. The increases in abundance of Deschampsia caespitose, Alopecurus pratensis, Holcus lanatus , and Anthoxanthum odoratum indicated the progressive degradation of fresh hay meadow communities attributed to the cessation of mowing. The expansive species Urtica dioica increased in abundance and persistence with reduced mowing intensity. Alien species such as Solidago canadensis and S. gigantea were noticed mainly in abandoned areas for at least five years.