This paper aims in assessing the relationship between grassland plant diversity and agronomic value, which represents a major challenge to reconcile nature conservation and agricultural use of semi-natural grassland habitats. The effects of plant diversity and functional traits were studied on forage nutritive value and early standing biomass in a wide set of semi-natural temperate grassland habitats. Plant communities were described by their species and functional diversity, community-weighted means (CWM) of plant functional traits, and the relative cover of main plant functional types (graminoids, forbs, and legumes). Species richness was found to be negatively associated with early standing biomass and average mineral content. Community evenness, for both species and plant functional types, was positively correlated with digestibility, crude protein content, and average mineral content but negatively with early standing biomass. Early standing biomass was found to increase with increasing graminoid cover and to decrease with increasing forb cover. Forage nutritive value improved with higher legume cover, higher specific leaf area CWM and lower leaf dry matter content CWM, while these functional community characteristics were not found to impact early standing biomass. Our results highlight that a better forage nutritive value can be obtained with a higher plant species evenness in permanent grassland habitats. Furthermore, in grasslands with an even distribution of plant functional types, forage nutritive value may be improved with no loss in early standing biomass.< Réduire