Species-rich alpine grasslands with Nardus stricta are important communities for both animal production and environmental conservation in Europe. We selected two contrasting types of Nardus grasslands (mesic and wet) within a rangeland of northern Spain and measured annual above-ground net primary productivity (ANPP), botanical components, forage utilization and their respective seasonal patterns, during a 5-year period. We analysed their chemical properties and recorded soil moisture and temperature in order to construct models able to explain grassland productivity. Mean annual ANPP of mesic Nardus grassland was about half (216 g DM m−2 year−1; ±29·8 s.e.) that of the wet grassland (406 g DM m−2 year−1; ±54·3 s.e.), with significant intra- and interannual variability. Mesic grassland, with a more important contribution of forbs and legumes over graminoids in its botanical composition, was the preferred forage source of grazing livestock and showed better chemical properties in spring and early summer. In summer and autumn, wet grassland had a higher utilization owing to its ability to maintain high biomass production. This was partially explained by soil moisture, a limiting factor of mesic grassland productivity. Our results provide new and relevant information on key aspects of species-rich alpine Nardus grasslands, potentially useful for the definition of management options for these habitats of priority conservation.