Ecological rarity, characterized by low abundance or limited distribution, is typical of most species, yet our understanding of what factors contribute to the persistence of rare species remains limited. Consequently, little is also known about whether rare species might respond diferently than common species to direct (e.g., abiotic) and indirect (e.g., biotic) efects of climate change. We investigated the efects of warming and exclusion of large herbivores on 14 tundra taxa, three of which were common and 11 of which were rare, at an inland, low-arctic study site near Kangerlussuaq, Greenland. Across all taxa, pooled commonness was reduced by experimental warming, and more strongly under herbivore exclusion than under herbivory. However, taxon-specifc analyses revealed that although warming elicited variable efects on commonness, herbivore exclusion disproportionately reduced the commonness of rare taxa. Over the 15-year duration of the experiment, we also observed trends in commonness and rarity under all treatments through time. Sitewide commonness increased for two common taxa, the deciduous shrubs Betula nana and Salix glauca, and declined in six other taxa, all of which were rare. Rates of increase or decline in commonness (i.e., temporal trends over the duration of the experiment) were strongly related to baseline commonness of taxa early in the experiment under all treatments except warming with grazing. Hence, commonness itself may be a strong predictor of species’ responses to climate change in the arctic tundra biome, but large herbivores may mediate such responses in rare taxa, perhaps facilitating their persistence. p. 4: "The interaction between warming and herbivore exclusion infuenced commonness of five taxa: B. nana, S. glauca, Aulacomnium sp., S. longipes, and Peltigera sp. (Supplemental Table S1)." ...; "and warming reduced commonness of the lichen Peltigera sp. under herbivore exclusion but increased its commonness under grazing (Fig. 2)."