Above-ground growth response of the bilberry (Vaccinium myrtillus L.) to simulated herbivory

Summary To monitor growth response in the bilberry to herbivory caused by small rodents, a field branch cutting experiment was conducted. Two damage patterns were used. In the first, all annual branches except the oldest stem were removed (R1). In the second, only half of the branches were removed (R2). The above-ground growth and fecundity were monitored for three growth seasons. Survival was over 80 %. The above-ground vegetative growth was vigorous, being 1.3-1.4 or 1.7-fold for R1 and R2 ramets, respectively, as compared with the respective control ramets. Increase in biomass in R1 ramets was a consequence of the larger sizes of the annual branches and leaves, whereas in R2 ramets both the number and the size of the branches and leaves increased. Flower production decreased during the following growth seasons in R2 ramets, and fewer flowers developed into berries. Abundant sexual reproduction would apparently have been too costly for the stressed plants. The more pronounced treatment, R1, rejuvenated the ramets to a vegetative state and these started producing berries only in the third season following damage. In general, the main effect of the damage was clearly to cause rejuvenation in bilberry ramets. The reduced limitation imposed by old tissue overrode the negative effects of biomass loss, which indicates the existence of an efficient buffer system in this clonal species against stress.