Abstract:

Aim: The interactions between herbivorous insects and woody plants have attracted wide attention due to their critical roles in ecosystems. So far, an increasing number of studies have investigated the distribution patterns of leaf herbivory intensity across the forest and the underlying factors influencing it. Consequently, numerous hypotheses have been proposed in the context. However, these hypotheses may not be universally applicable across different forest communities. In particular, systematic validation in mid-subtropical evergreen broad-leaved forests remains limited. Moreover, current research has predominantly focused on a limited number of species, and the extent to which these findings can be generalized to the entire forest community requires further investigation and verification. 

Methods: In this study, we investigated 400 individuals from 149 broad-leaved tree species in a 25-ha subtropical forest dynamics plot at Baishanzu (Baishanzu plot), Zhejiang Province. First, interspecific differences in leaf herbivory intensity (herbivory rate and frequency) were compared among tree species. And then, based on the plot data, a generalized linear mixed model was used to systematically investigate the effects of sampled tree species categories (classified by tree life form and abundance), leaf size, neighboring tree diversity and composition, and soil nutrients on herbivory rate (the proportion of leaf area consumed by herbivory), with the aim of identifying the dominant factors driving herbivory rate in the Baishanzu plot. 

Results: (1) 99.40% of herbivory in the plot was caused by chewing insects. The average herbivory rate was 7.18%, and the average herbivory frequency was 65.38%. There were significant differences in herbivory rate and frequency among different tree species. Moreover, the herbivory rate of evergreen species was significantly higher than that of deciduous species, common species were significantly higher than rare species, and tree species were significantly higher than shrub species; (2) The results of the model indicated that tree categories significantly influenced herbivory rate, and there was a significant positive correlation between herbivory rate and the phylogenetic diversity of neighboring trees. Furthermore, the results of the variance decomposition showed that tree life form (tree vs. shrub) exhibited the highest relative contribution, accounting for 62.33% of the explained variation. 

Conclusion: The findings of this study corroborated the plant-apparency hypothesis regarding insect herbivory, indicating that evergreen, common, and tree species experienced greater levels of herbivory due to their higher apparency within the community. Additionally, this study also revealed the existence of an associational susceptibility effect in the Baishanzu plot, suggesting that mixtures of phylogenetically distant trees resulted in more severe insect herbivory.

Key words: subtropical forest, herbivory intensity, life form, interspecific variation, plant apparency hypothesis, associational susceptibility effect