Plant-herbivore interaction is one of the most important trophic interaction in terrestrial ecosystems. About 10-20 % of plant biomass produced in a year is said to be consumed by herbivores. Consequently, herbivores can affect plant fitness, community assembly, and ecosystem functions such as productivity or nutrient cycling. Susceptibility to herbivores largely varies among plant species, and many previous studies have investigated what factors determine the species’ herbivory rate. Each study sometimes found that herbivory rate was influenced by plant species’ functional traits (e.g., nutrition or secondary metabolites), individual density, or ontogeny; however, it has been rarely investigated how these factors collectively affect herbivory, especially at a community of diverse woody species.
In this study, we tested how the ontogeny (saplings or adults) affect the relationships between plant species’ characteristics (functional traits, mean basal area (BA), individual density) and leaf herbivory rate by using ca. 50 woody species in a temperate forest in Japan. The following specific questions are focused; (1) how are the plant species’ characteristics and the herbivory rate different between saplings and adults? (2) which factors mostly explain species’ herbivory rate and how are the relationships between plant species’ characteristics and herbivory different between saplings and adults?
Results/Conclusions
Most characteristics (e.g., leaf mass per area (LMA), individual leaf area, leaf strength, foliar nitrogen, foliar phenolics) were correlated between saplings and adults among the studied species. The functional traits such as LMA, leaf strength, foliar total phenolics and condensed tannins were generally higher for adults than for saplings, while foliar water content and individual density showed the opposite trend. Foliar nutrition (P and N) and individual leaf area were not different between saplings and adults. The observed leaf herbivory rate was also not different between saplings and adults among the studied species. The best model predicting herbivory showed that individual leaf area and species’ mean BA were keys for species’ herbivory rates, and the relationships between species’ mean BA and herbivory were different between saplings and adults. The adults were generally more susceptible to herbivores than saplings when these characteristics were same. Thus, even though the adults seemed to have tougher and better-defended leaves than saplings, such traits did not explain the differences in species’ herbivory rate. Furthermore, some unmeasured mechanisms that make adults more susceptible to herbivores might be responsible for the similar herbivory rate observed for saplings and adults in this studied forest.