Compensatory growth of two clonal dwarf shrubs, Arctostaphylos uva-ursi and Vaccinium uliginosum in a heavy metal polluted environment

The effect of artificial shoot clipping on the vegetative growth and sexual reproduction of the evergreen bearberry, Arctostaphylos uva-ursi, and the deciduous bog bilberry, Vaccinium uliginosum, was studied in the vicinity o f a copper-nickel smelter in SW Finland. According to the research hypothes is, heavy metal induced shoot death breaks the apical dominance in the clon es growing in a polluted environment. This causes activation of dormant axi llary and adventitious buds and an increase in branching on the older parts of the stem. Regrowth after shoot death was studied by clipping off all th e current-year shoots from experimental branches in autumn (1994) and sprin g (1995). Within-clone and between-clone control branches were used to test the data. Both species displayed a considerable ability to activate dormant meristems after the damage. Regrowth of the current shoots during the next growing s eason (1995) was about 80% compared to the within-clone control in both spe cies after autumn clipping. Shoot clipping in early summer was more detrime ntal for both species, and the regrowth of A. uva-ursi was less than that o f V. uliginosum. Differences in the storage reserves and source-sink mechan isms of carbon allocation between evergreen and deciduous species probably explain their distinct response. When the removed biomass was added to the living biomass of the branches, there was overcompensation in the total dry weight of A. uva-ursi after autumn clipping, and the weight was almost 90% of the control after spring clipping. The total dry weight of V. uliginosu m also equalled that of the control when the removed biomass was added. No berries developed on either species in the year following the autumn treatm ent, because clipping removed all the flower buds. Spring clipping had no e ffect on the sexual reproduction of A. uva-ursi, but decreased the berry pr oduction of V. uliginosum. The degree of compensatory growth of both specie s was only slightly affected by the distance from the smelter. It is sugges ted that dormant bud activation, rapid regrowth and plastic branching contr ibute to the resistance mechanism to heavy metals.