ABOVEGROUND GROWTH-RESPONSE OF THE BILBERRY (VACCINIUM-MYRTILLUS L) TO SIMULATED HERBIVORY

To monitor growth response in the bilberry to herbivory caused by smal l rodents, a field branch cutting experiment was conducted. Two damage patterns were used. In the first, all annual branches except the olde st stem were removed (R 1). In the second, only half of the branches w ere removed (R2). The above-ground growth and fecundity were monitored for three growth seasons. Survival was over 80 %. The above-ground ve getative growth was vigorous, being 1.3-1.4 or 1.7-fold for R 1 and R 2 ramets, respectively, as compared with the respective control ramets . Increase in biomass in R 1 ramets was a consequence of the larger si zes of the annual branches and leaves, whereas in R 2 ramets both the number and the size of the branches and leaves increased. Flower produ ction decreased during the following growth seasons in R 2 ramets, and fewer flowers developed into berries. Abundant sexual reproduction wo uld apparently have been too costly for the stressed plants. The more pronounced treatment, R 1, rejuvenated the ramets to a vegetative stat e and these started producing berries only in the third season followi ng damage. In general, the main effect of die damage was clearly to ca use rejuvenation in bilberry ramets. The reduced limitation imposed by old tissue overrode the negative effects of biomass loss, which indic ates the existence of an efficient buffer system in this clonal specie s against stress.