THE IMPACT OF HERBIVORY AND COMPETITION ON THE PHENOLIC CONCENTRATION AND PALATABILITY OF JUVENILE BIRCHES

Plant chemical characteristics in many cases have a profound impact on herbivore food preference. However, our knowledge of how biotic factors influence plant chemistry and palatability is limited. To evaluate how intraspecific competition and herbivory affects chemistry and palatability of woody plant seedlings to herbivores, we subjected birch (Betula pubescens) seedlings to three density treatments and two types of simulated herbivory: total defoliation and removal of all aboveground biomass. Both the density- and herbivory-treatment reduced plant growth. A negative correlation was also apparent between plant density and plant phenolic concentration. However, a bioassay with caged voles (Microtus agrestis) revealed no differences in palatability between birches in different density groups. The concentration of total phenolics did not differ between treatment groups and controls in the simulated herbivory treatments. However, the voles preferred defoliated plants over control plants and clipped plants. The reason for this is not clear. One explanation could be that different types of damage result in qualitative differences in plant chemistry.