Seasonal differences in insect herbivory on woody plant seedlings along a subtropical elevational gradient

<b>Premise: </b>Theories of plant-herbivore interactions hold that seedlings are more vulnerable to herbivory in warmer and more stable climates at lower elevations. Hypotheses of plant apparency, resource concentration, and resource availability have been proposed to explain the variability in leaf herbivory. However, the seasonal differences of leaf herbivory on seedlings remain unclear.<b>Methods: </b>To address this issue, we measured the percent and frequency of leaf herbivory in understory seedling communities within a subtropical forest during two seasons (May and October), covering an elevational gradient from 290 m to 1370 m. In total, 2,890 leaves across 696 seedling individuals belonging to 95 species were measured. Beta regression analyses were used to assess the effects of biotic and abiotic factors (leaf area, seedling height, community height, plant diversity, light, and soil nutrients) on leaf herbivory.<b>Key results: </b>Plant seedlings exhibited single-peaked elevational patterns of percent and frequency leaf herbivory. The effects of drivers on leaf herbivory varied in two seasons. Leaf herbivory was influenced by leaf area, seedling height, plant diversity, canopy openness, and soil nutrients in May, while mediated mainly by seedling height, plant diversity, canopy openness, and soil nutrients in October. The findings are only consistent with the resource concentration hypothesis, with lower leaf herbivory on seedling leaves in high plant diversity, but not with the results predicted by the plant apparency and resource availability hypotheses.<b>Conclusions: </b>Overall, our study highlights the importance of seasonal herbivory differences toward a comprehensive understanding of leaf herbivory in subtropical forests.