GROWTH AND REPRODUCTION OF DWARF SHRUBS IN A SUB-ARCTIC PLANT COMMUNITY - ANNUAL VARIATION AND ABOVEGROUND INTERACTIONS WITH NEIGHBORS

1 The effects of coexisting shrub species on the growth, branching, survival and berry production of three dominant dwarf shrubs (Empetrum nigrum, Vaccinium vitis-idaea and V, uliginosum) were examined in northern Finland in a six year experiment. The measurements covered both natural, unmanipulated plots as well as plots from which ramets of one of five dwarf shrub species had been removed. 2 Annual patterns of growth and reproduction of ramets of the three species were different, suggesting that the plants were affected by different combinations of environmental factors and internal patterns of ramet growth. Neither cumulative summer temperature nor summer precipitation accounted for the variations in annual growth of any dwarf shrub species; however, ramet age contributed significantly to the observed variation in growth of shoots of V. vitis-idaea and V. uliginosum. 3 The growth of ramets of E. nigrum in unmanipulated plots was positively correlated with the cover of V. myrtillus and total cover of dwarf shrubs; the growth of V. uliginosum was similarly correlated with the cover of V, myrtillus in undisturbed plots. Furthermore, the growth of both E. nigrum and V. uliginosum was reduced by the removal of V. uliginosum and V. myrtillus, respectively. These observations probably indicate some kind of positive relationship between these species. By contrast, the shoot growth of V. vitis-idaea was less and mortality greater in unmanipulated plots where V. uliginosum was abundant, while both branching and reproduction of V. vitis-idaea were increased by the removal of other dwarf shrubs. These results indicate that interspecific competition may limit the growth and reproduction of V. vitis-idaea.