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, su rvival and berry production of three dominant dwarf shrubs (Empetrum n igrum, Vaccinium vitis-idaea and V, uliginosum) were examined in north ern Finland in a six year experiment. The measurements covered both na tural, unmanipulated plots as well as plots from which ramets of one o f five dwarf shrub species had been removed. 2 Annual patterns of grow th and reproduction of ramets of the three species were different, sug gesting that the plants were affected by different combinations of env ironmental factors and internal patterns of ramet growth. Neither cumu lative summer temperature nor summer precipitation accounted for the v ariations in annual growth of any dwarf shrub species; however, ramet age contributed significantly to the observed variation in growth of s hoots of V. vitis-idaea and V. uliginosum. 3 The growth of ramets of E . nigrum in unmanipulated plots was positively correlated with the cov er of V. myrtillus and total cover of dwarf shrubs; the growth of V. u liginosum was similarly correlated with the cover of V, myrtillus in u ndisturbed plots. Furthermore, the growth of both E. nigrum and V. uli ginosum was reduced by the removal of V. uliginosum and V. myrtillus, respectively. These observations probably indicate some kind of positi ve relationship between these species. By contrast, the shoot growth o f V. vitis-idaea was less and mortality greater in unmanipulated plots where V. uliginosum was abundant, while both branching and reproducti on of V. vitis-idaea were increased by the removal of other dwarf shru bs. These results indicate that interspecific competition may limit th e growth and reproduction of V. vitis-idaea.