Five grassland species (Dactylis glomerata, Festuca arundinacea, F. rubra, Poa pratensis and Trisetum flavescens) were cultivated in monoculture and in mixture with a highly competitive cultivar of Dactylis glomerata (Lupre) in 2002 at Theix, Massif Central, France. This setup aimed to evaluate the impact of species interactions on the productivity and on the nutritive value of these grassland species differing in their growth strategies. All 5 species exhibited larger aboveground organs when submitted to competition with the cultivar and this was associated to an increase in the proportion of structural tissue and to a decline in their nutritive value. Aboveground production in competition increased for tall species but decreased for the small ones. For small species, frequent defoliation regime balanced the negative effect of competition.