In the framework of a nature conservation project in a wetland region of Meetkerke, Belgium, a comprehensive study was conducted to analyse and to compare species composition and diversity among wet grasslands under the six following types of agricultural land use: pastures used at high or low stocking rate, hayfields used at high or low mowing frequency, abandoned hayfields and hay pastures. The focus of the study was on the effects of grassland management on species diversity and on the restriction of occurrence of invasive clonal species. The results show that species importance was strongly related to grassland exploitation parameters and soil hydrological parameters, as shown by the ordination diagram drawn by canonical correspondence analysis (CCA). Species number and importance of non-leguminous dicotyledons were negatively correlated to intensity of use, N supply, water table depth and soil drainage. Phalaris arundinacea, an invasive species which might reduce species diversity, was better suppressed in grazed grassland than in mown grassland. Phalaris arundinacea and Cirsium arvense were most prevalent in abandoned hayfields. Grazing at low stocking rate was the best management technique to maximise plant diversity while restricting invasion by nitrophilous clonal species. Although species-rich and of high complementary value on a landscape scale, haylands mown at low frequency are at higher risk of invasion by clonal species.