Forest restoration under leaf-cutting ant pressure: distance from ant nests and plastic tree shelters improve sapling survival

Abstract

Forest restoration is a great challenge when saplings are repeatedly pruned by leaf-cutting ants and pesticides are not permitted. Based on four hypotheses (distance-dependent foraging, plant repellence, structural complexity, and nutrient content), we predicted that sapling performance increases and ant pruning decreases: (1) away from leaf-cutting ant nests; (2) in unpalatable or (3) tall vegetation patches; and (4) in non-fertilized soils. We set up a full factorial field experiment to test the hypotheses; we also monitored sapling performance without and with plastic tree shelters used by practitioners to deter ant pruning. Our results showed predicted sapling survival from 40 to 80% per year for distances to nests ranging from 4 to 223 m, respectively. Ant pruning decreased with increasing distance, with null pruning at distances >121 m. Variation in sapling survival, but not in ant pruning, was also explained by the interaction between vegetation palatability and nutrient condition. Vegetation height did not explain sapling survival or pruning. Plastic tree shelters increased survival by 3.5 times and reduced pruning by half. Height of surviving saplings was not affected by any treatment. Our results show the potential for active forest restoration without the use of tree shelters away from leaf-cutting ant nests, while tree shelters are a viable option near leaf-cutting ant nests.