Since 1989, the effects of an experimental management by mowing at different periods of the year have been followed in a limestone grassland of the " Abannets " plateau (Nismes - province de Namur). The evolution in 6 managed and 2 unmanaged quadrats (each of 100 m2) has been compared, using the number of flowers/inflorescences produced, the diversity of plant species/m2 and the dynamic of orchid populations as indicators. The results showed a positive response for most of the species between 1989 and 1995. Since 1995, the contrasted responses observed could be due to the development of a dense, close herb layer and the regression of the gaps in the canopy (regeneration niches). The results have been used to adapt the management plans of the nature reserves in Wallony.