Increasing temperature imperils worldwide tropical subalpine and alpine ecosystems with the threat of mountaintop extinctions and a subsequent loss of biodiversity and ecosystem functions. This paper provides a first assessment of functional diversity along a high climatic gradient for bryophytes, which represent a major plant compartment in these ecosystems. The present study takes place on the highlands of the Piton des Neiges volcano, the highest summit of La Réunion Island (Western Indian Ocean). We find a relatively high species richness of bryophytes in these subalpine habitats, with a peak of diversity at 2750 m for the ground-dwelling community. We report a strong linear relationship between functional diversity and species richness for epiphytes. Within the same plant group, the relationship between functional richness, based on eight traits, and elevation differed between the ground-dwelling and epiphytic communities, suggesting that different processes may structure bryophyte species assemblages along this short subalpine climatic gradient. Higher functional redundancy in ground-dwelling bryophyte assemblages indicates that this community may be more robust than epiphytic bryophytes to disturbances in these subalpine ecosystems.