RESPONSES TO HARVESTING INTENSITY IN A CLONAL DWARF SHRUB, THE BILBERRY (VACCINIUM-MYRTILLUS L)

The effects of herbivory were simulated on stands of bilberry (Vaccini um myrtillus L.) in a boreal Empetrum-Myrtillus type forest. Five harv esting intensities were used (0 % (A), 25 % (B), 50 % (C), 100 % (D) o f the bilberry ramets or all the ramets of all species (E)). Density a nd biomass of the stands, and growth of the ramets were monitored for five growth seasons, from 1986 to 1990. After damage new ramets emerge d rapidly from dormant buds at the base of removed ramets. Between 70 and 97 % of the density relative to the control level was regained by the final harvest. However, only between 11 and 64 % of the biomass re lative to the control level was recovered. Clipping reduced the branch growth, both in the new ramets and in the new parts of the old, uncli pped ramets. Severe treatments (D and E) decreased the growth more tha n did light harvesting (B and C). Survival and fecundity of the ramets were not affected. The result therefore suggested that the bilberry i s not able to recover totally from severe herbivory damage between the years of peak rodent population that shows a 3-4 year cycle. Neverthe less, extreme grazing pressure is rare in boreal ecosystems as alterna tive food is available for herbivores, and predators also limit the he rbivore population. Hence the bilberry exhibits moderate tolerance of the usual level of herbivory damage.