Trait–climate mediation, not herbivory avoidance, shapes leaf emergence strategies in global dry tropics

Dry tropical ecosystems contribute nearly 40% of the interannual variability in global terrestrial carbon exchange, yet the driver of leaf emergence timing, a key determinant of ecosystem productivity, remains uncertain. Competing hypotheses emphasize rainfall cues or avoidance of herbivory, but their relative roles are unresolved at a pan-tropical scale. Here, using global data on satellite-based phenology, climate, plant traits, and ground-based insect occurrence, we show that leaf emergence across the dry tropics is closely synchronized with insect outbreak timing, contradicting the herbivory-avoidance hypothesis. Instead, in ~90% of the region, leaves emerge before the rainy-season begins: forests lead rainfall by 40.3±24.3 days, compared with shrublands (22.1±21.4 days) and grasslands (20.0±21.3 days). The stronger advances in forests likely reflect integrated trait-mediated adaptations, with deeper rooting, greater stem water reserves, and tighter stomatal regulation enabling them to mobilize pre-season moisture. These traits, together with wetter climate, extend the growing period and reduce phenological sensitivity to decadal rainfall variability by ~50% relative to non-forest systems, conferring greater stability under decadal climate shifts. These findings falsify the herbivory-avoidance hypothesis and identify trait‑climate mediation as key drivers of dry tropical phenology, offering a mechanistic basis to improve carbon-cycle models, assess climate impacts, and inform adaptation strategies.