In recent decades, the use of some subalpine mountain grasslands in the Central Spanish Pyrenees has changed. Ski resorts have been developed and cattle herd management has shifted from the traditional “rotational-type” system in which grazing cattle are overseen by a herder to a “continuous-type” system that does not involve a herder. In 2005, the locations of 30 floristic inventories performed in 1972 were revisited and inventories were repeated in two adjacent similar areas, although one had been used for the development of ski runs and the other had not. The objective was to assess the effects of those changes on plant diversity and other characteristics of the grasslands. In both areas, plant diversity was significantly higher in 2005 than it was in 1972. Both areas had been grazed by cattle to a similar extent; thus, the results suggest that diversity was affected primarily by the change in the livestock grazing system. Livestock grazing within the skiing area appears to have counterbalanced any reduction in plant diversity that would have occurred because of the construction and use of ski runs. In the skiing area, legume cover and pastoral value decreased, the Ellenberg Nitrogen Index reflected lower soil nutrients available to plants, and the cover of plant species that regenerate by seeds increased between 1972 and 2005; such changes did not occur in the non-skiing area. The abundance of ruderal species increased more in the skiing area than in the non-skiing area. Between 1981 and 2000, the amount of bare ground increased only in the skiing area.