ABSTRACT Land-use change is the main cause of biodiversity losses, and for grasslands includes changes in management. The last 10 years has seen afforestation of traditionally grazed grasslands increase considerably in the understudied Serra do Sudeste region of the Brazilian Pampa, turning the region into a mosaic of tree plantations, natural ecosystems (partly in conservation areas without grazing management) and other land uses. We evaluated grassland plant community structure and composition in conservation areas considering two distinct types of land-use history and compared them to grasslands under traditional management. The study was carried out at 58 sites. Per site, three plots were established to sample the plant composition of the herbaceous and shrub layers. We used ordination techniques and indicator species analysis to describe patterns of community composition. We recorded a total of 516 species, thus confirming the high biodiversity of the region. We detected differences in vegetation structure and composition between primary and secondary grasslands. Our study emphasizes the need to increase conservation efforts in the region and points out that current conservation approaches should be evaluated critically regarding their effects for biodiversity conservation and that adequate grazing management is key for grassland biodiversity conservation.