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Background: The presence of plants is crucial in securing steep slopes against soil erosion. Inappropriate land use in mountains often leads to vegetation loss and thus soil degradation. Aims: Here we ask if the edges of large erosion gullies select for specialist plant species that reduce or prevent the progression of soil loss. Methods: We quantified species presence and abundance across micro-transects from intact mountain pastures toward the edge of erosion gullies at ca. 1900 m elevation in the Central Caucasus, Georgia. Results: Out of a large species pool, one particular species, Festuca valesiaca, was the dominant species at the very edge of erosion gullies. Increased C values in Festuca valesiaca leaves by 1.1% towards the edge confirmed that this species copes best with the dry conditions at the edge. Conclusion: Our findings illustrate the insurance effect of a highly diverse vegetation. The importance of a single species out of this diverse species suite to sustain key ecosystem functions becomes apparent only under extreme environmental conditions; in this case, at edges of erosion gullies.