Questions: Humans are altering land use and impacting grazing intensities worldwide in alpine and sub-alpine grasslands, and functional diversity (FD) is a useful tool for predicting changes in these grassland communities and for improving biodiversity conservation. We asked: (1) how does functional richness (FRic) differ between the five predominant grassland types in Andorra (2) of these five grassland types, which plant communities are subject to high habitat filtering and which are driven primarily by competitive interactions; (3) are certain grassland communities more prone to degradation than others; and (4) how do grazing intensity and elevation influence variations in FD indices? Locations: Five types of sub-alpine and alpine grassland communities dominated by Festuca airoides, F. eskia, F. gautieri, F. paniculata and Nardus stricta in Andorra, at various elevations and with differing grazing intensities within a grassland type. Methods: We used multiple functional diversity indices and structural equation modelling (SEM) to determine how grazing intensity, elevation, species richness and productivity affect functional diversity in 222 vegetation transects. Results: Both plant diversity and functional richness were higher at higher grazing intensities, with the highest values found in the F. gautieri and F. paniculata grasslands and lowest in the Nardus stricta, F. airoides and F. eskia grasslands. Habitat filtering was observed in F. airoides grasslands. There was a general tendency for higher competitive interactions among plants at higher elevations and/or when species diversity increased. None of the five grassland communities considered appears disturbed, and all present similar functional attributes between dominant species. Conclusions: Our results highlight the fact that grazing is an integral part of Andorran mountain grasslands, acting as a structural component and providing higher functional richness in the most grazed communities.