Community leaf dry matter content mediates the impact of mixture composition on forage yield and nutritive value in temporary mountain grasslands

Mountain forage production is increasingly threatened by grassland degradation and limited adaptation to climate change. Regenerating these grasslands with multispecies forage mixtures adapted to altitude and future climatic conditions may enhance the sustainability of livestock systems. We conducted a field study across four mountain grassland sites in Switzerland, experimentally manipulating the dominant species identity ( Dactylis glomerata and/or Alopecurus pratensis ) and the proportion of low-abundant species in sown mixtures (0, 15 or 30%), including Plantago lanceolata . We measured forage yield, protein and neutral detergent fiber (NDF) over three harvests during the growing season, and quantified specific leaf area (SLA) and leaf dry matter content (LDMC) of all species to characterize community functional strategies. We found that the botanical composition influenced yield and NDF primarily through shifts in community functional traits mostly related to LDMC, whereas it mostly influenced protein concentration through direct effects from legumes. Forage yield was not influenced by the identity of the dominant species but increased with an increasing abundance of P. lanceolata at the second harvest in summer. Across the season, forage NDF concentration increased with increasing abundance of the two dominant grasses but decreased with increasing abundance of P. lanceolata and legumes . Overall, our findings demonstrate that integrating P. lanceolata , a species with low LDMC, into forage mixtures can enhance seasonal stability in forage production through complementarity with dominant grasses and improve forage nutritive value. These results highlight the importance of trait-based species selection for designing resilient forage mixtures adapted to mountain environments.