Dynamics of insect herbivory on seedling growth: A three-year study reveals metric-specific effects and resilience in a subtropical forest

Insect herbivory is a key driver of forest regeneration, yet its effects on woody seedlings in subtropical forests remain inadequately quantified. We conducted a three-year study (2022–2024) in the Ailao Mountains, a subtropical montane evergreen broadleaved forest in Yunnan, China, which represents a globally significant biodiversity hotspot. Our results showed that mean community-level cumulative herbivory remained relatively stable across years (5.4–6.3%). However, the effects of herbivory on seedling growth exhibited strong interannual variation: negligible in 2022, negative in 2023, and divergent in 2024 (positively correlated with height growth but negatively with leaf number growth). These temporal shifts were closely linked to interannual variability in early rainy-season precipitation, whereas temperature played a negligible role. Growth responses also varied substantially among species, even under comparable herbivory pressure. Notably, herbivory had no significant effect on seedling survival in any year. Our findings demonstrate that herbivory effects on subtropical seedlings are context-dependent (mediated by rainfall), growth-metric-specific, and species-specific. We conclude that subtropical montane seedlings are resilient to moderate herbivory, providing scientific support for the non-intervention approach to herbivore management in protected forests. Nevertheless, climate-driven alterations in rainfall seasonality could disrupt these ecological relationships, underscoring the importance of long-term monitoring for informing adaptive forest management strategies.