Leaf-cutting ants are dominant herbivorous insects that play a key role in ecosystem dynamics. In recent decades, their populations have expanded in fragmented, disturbed or modified forests, highlighting the need to understand their responses to environmental change. We examined how fire, grazing, and vegetation structure affect the nest occurrence of Acromyrmex lobicornis and Acromyrmex crassispinus, the dominant leaf-cutting ants in the mountains of central Argentina. We conducted stratified random sampling across habitats along an elevation gradient and used generalized linear models to assess the influence of topographic, vegetation and disturbance-related variables on nest occurrence. Of the 250 plots surveyed, A. lobicornis was found in 18.8 % of plots (1.49 nests/ha) and A. crassispinus in 14.1 % (1.12 nests/ha), within their respective elevational ranges. Both species were least frequent in conserved native forests, confirming their preference for open, disturbed or modified habitats. However, their responses diverged. A. lobicornis was directly associated with disturbance, occurring more often in recently burned areas and sites with intense livestock activity. In contrast, A. crassispinus was linked mainly to vegetation structures shaped by long-term disturbance and habitat modification, thriving in rocky open areas and exotic forests with sparse understory and extensive bare soil beneath the canopy. Overall, forest modification or degradation opens the door to leaf-cutting ants by creating open or bare habitats, while species-specific traits determine the magnitude and pathways of this response. From a management perspective, conserving mature forests as refugia from leaf-cutting ants, and protecting forest regeneration in degraded areas should be prioritized.
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