Forage nutritive value shows synergies with plant diversity in a wide range of semi-natural grassland habitats

Preprint in SSRNAssessing the relationship between grassland plant diversity and agronomic value is a major challenge to reconcile nature conservation and agricultural use of extensive grassland habitats. To do this, multiple facets of forage production must be considered such as the quantity produced and its nutritive value, commonly assessed through its digestibility, energy content, and nutrient content. The aim of this study was to analyse the effects of plant diversity and functional traits on forage productivity and nutritive value in a wide set of semi-natural grassland habitats.Forage was sampled in 202 plots located across 68 permanent extensive grasslands in eight regions of France. Species and functional diversity indices, community-weighted means (CWM) of plant functional traits, and the relative cover of main plant functional types (PFT; graminoids, forbs, and legumes) were used to describe plant communities. Forage production was evaluated by recording early standing biomass (SB), and nutritive value parameters, namely digestibility (DMD), crude protein content (CP), and average mineral content (MinAv) at the beginning of the vegetation growing season.Species richness was negatively associated with SB and MinAv. Species evenness was positively correlated with CP, DMD, and MinAv, while PFT evenness was positively correlated with CP and DMD. Forage standing biomass increased with increasing graminoid cover and decreased with increasing forb cover. A higher legume cover and specific leaf area CWM as well as a lower leaf dry matter content CWM was associated with improved forage nutritive value and had no effect on SB. 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