Natural Biofortification in Semi-Natural Mountain Meadows: Ecological Drivers of Forage Trace Mineral Profiles

Trace mineral dynamics in mountain pastures remain poorly quantified. This study evaluates the ecological drivers of forage micronutrient profiles (Fe, Cu, Mn, Zn) across 12 Pyrenean hay meadows. Over 3 years, 212 forage samples were analysed for botanical composition, standing biomass, and mineral content. Data were evaluated using PCA, Structural Equation Modelling (SEM), and tertile abundance partitioning. Subclinical Mn (47.5 ± 39.2 mg kg−1 DM) and Zn (22.4 ± 9.3 mg kg−1 DM) deficiencies were widespread. Non-leguminous forb cover drove Zn (R2 = 0.550, p < 0.001) and Cu (R2 = 0.428, p < 0.001) enrichment, reaching a target functional threshold at 20% to 25% cover without reducing biomass yield. Conversely, grass-dominated swards increased total ash via silica rather than trace minerals. Mn dynamics responded to thermal time, whereas Fe depended largely on soil contamination. Maintaining a 20% to 25% forbs cover target offers a practical, low-cost strategy to secure trace element self-sufficiency in extensive mountain livestock systems.