Herbivory intensity and plant species traits interact with tree canopy cover to drive seedling survival in Neotropical savannas

Herbivory plays a crucial role in shaping vegetation dynamics. In the Brazilian Cerrado, the abundant and widespread presence of leaf-cutter ants contributes to the prevalence of high levels of chewing insect damage. However, the influence of increased herbivory on seedling survival remains largely untested in experimental settings. Furthermore, it is unclear how plant species traits affect seedling responses in savanna areas with contrasting canopy cover. To address these gaps, we transplanted seedlings from 10 native woody species into open and closed savanna areas in the Panga Ecological Reserve, Brazil, and evaluated long-term survival under four levels of simulated herbivory. We also tested the role of seed mass and resprouting capacity in seedling survival across species. We found that moderate herbivory (50% defoliation) did not reduce seedling survival compared with undamaged plants, regardless of the savanna area. However, severe damage (100% defoliation and shoot system removal) increased mortality two- to three-fold. Overall, seedling survival was lower in the open savanna area than in the closed savanna area across all herbivory levels. However, while tree canopies reduced environmental stress, they also limited seedling recovery from severe herbivory, resulting in a greater relative increase in mortality for damaged seedlings in closed savannas. Seedling responses to herbivory also varied by species traits, with large-seeded species and those with greater resprouting often showing higher survival, particularly in the open savanna. These findings enhance our understanding of how herbivory may influence savanna vegetation dynamics, demonstrating that chewing insects compound the environmental stressors affecting seedling recruitment, with canopy cover modulating seedling-herbivore interactions across the heterogeneous landscapes of Neotropical savannas.