This study analyzed the link between organic beef production and agroecosystems in mountain areas and the potential effects of land use change in eight farms of Catalan Pyrenees with a three step approach: (i) assessment of structural and management features; (ii) comparison of forage productivity and manure loads of 71 farmland parcels in relation with management intensity (natural meadows, seminatural meadows, temporary crops) and, for meadow parcels, with the farmers’ willingness to convert them to temporary crops; (iii) life cycle assessment of the environmental impacts. Each farm managed around 150 ha of pastures and 23 ha of farmland (of which only 5 as temporary crops), and maintained a herd of around 130 livestock units. Forage productivity and manure loads of farmland were modest and extremely variable, and no productive advantages could be predicted from the conversion of meadows to temporary crops. Environmental impacts were mostly related to the on-farm stages, because of low-input management and very high feed self-sufficiency, and the diets used showed very low feed/food competition. These results indicate a balance between organic beef production and management of mountain agroecosystems, which is a key point for sustainability and should be a priority in European policies and strategies.