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

Abstract

Abstract Plant-herbivore interactions hold that seedlings are more vulnerable to insect predation in warmer and more stable climates at lower elevations. Several hypotheses of plant apparency, resource concentration, and resource availability have been proposed to explain the variability in leaf herbivory, but seasonal variations of leaf herbivory on seedlings are unclear. To address this, we measured the rate and frequency of leaf herbivory in understory seedling communities in a subtropical forest in two seasons (May and October), covering an elevational gradient from 290 m to 1370 m. Overall, 2,890 leaves of 696 seedling individuals belonging to 96 species. Simple linear models were used to assess the effects of biotic (leaf area, seedling height, community height, and plant diversity) and abiotic factors (light and soil nutrients) in leaf herbivory. Results showed that seedlings exhibited single-peaked elevational patterns of leaf herbivory rates and frequencies only early in May. The effects of drivers on leaf herbivory differed 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 and soil nutrients in October. The findings only support the resource concentration hypothesis, with lower leaf herbivory on seedling leaves in high plant diversity, but are contrary to those predicted by the hypotheses of plant apparency and resource availability. Overall, our study highlights the importance of seasonal herbivory variations toward a comprehensive understanding of leaf herbivory in subtropical forests.