Global change drivers alter weed performance and threaten forage production in an Andean agroecosystem

Climate change and other global drivers threaten the long-term sustainability of production systems in the Andean highlands. Impacts on forage production and weed competition have important implications for farmer livelihoods but have received only limited attention. This study examines the impact of key global change drivers on the performance of the common forage, Lolium multiflorum , grown in competition with two important weeds of the region ( Rumex acetosella or Pennisetum clandestinum ). Forage-weed mixtures were grown in field mesocosms at different elevations, as a proxy for climate (3520 and 3740 m a.s.l.) and under contrasting nutrient management strategies (manure vs. synthetic fertilizer) to reflect a trend of increasing fertilizer use in the region. The findings indicate that warming conditions negatively impacted L. multiflorum performance, while manure inputs increased overall biomass production by 27 % relative to synthetic fertilizer. Meanwhile the impacts of amendments on weed-crop competition were plant-specific. For instance, R. acetosella competed better with organic manure nutrients, whereas P. clandestinum performed better at warmer sites amended with synthetic fertilizer. Findings from this study suggest that climate warming may exacerbate weed pressures, threatening crop production and food security in Andean landscapes. Additionally, continued reliance on traditional nutrient management, instead of synthetic fertilizers, may help support forage productivity and resilience under changing climate conditions. • Organic management enhances forage biomass of the forage crop Lolium multiflorum. • L. multiflorum performs worse under warming conditions. • Pennisetum clandestinum competes better under warming conditions and with synthetic fertilizers. • Rumex acetosella competes better with organic (manure) management practices.