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Growth Response of Subarctic Dwarf Shrubs, Empetrum nigrum and Vaccinium vitis-idaea, to Manipulated Environmental Conditions and Species Removal

Anna Shevtsova, Erkki Haukioja and Arja Ojala
Oikos
Vol. 78, No. 3 (Apr., 1997), pp. 440-458
Published by: Wiley on behalf of Nordic Society Oikos
DOI: 10.2307/3545606
Stable URL: http://www.jstor.org/stable/3545606
Page Count: 19
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Growth Response of Subarctic Dwarf Shrubs, Empetrum nigrum and Vaccinium vitis-idaea, to Manipulated Environmental Conditions and Species Removal
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Abstract

We investigated the growth responses of two evergreen dwarf shrubs Empetrum nigrum and Vaccinium vitis-idaea to environmental manipulations (elevated temperature, increased precipitation and simulated acid rain) and to experimentally altered species composition in a three-year field experiment in the Finnish Subarctic. The responses of these species to experimental manipulations were highly complex, due to species-specific patterns of growth, great inter-annual variation and a high number of interactions between temperature, water and community composition. Both species showed increased shoot growth in the second and third season in response to elevated temperature. Elevated temperature also accelerated the vegetative bud break and shifted the peak shoot growth to an earlier time. The shoot growth of V. vitis-idaea was generally enhanced by additional irrigation, while the growth of E. nigrum tended to decrease in watered plots. Removal of heterospecific neighbours significantly modified growth responses to environmental manipulations. The positive effect of elevated temperature on E. nigrum was usually more profound on mixed species than on removal plots. The shoot growth of V. vitis-idaea was increased most when warming and watering were applied to plots of mixed species composition. The effect of the removal of companion species in turn depended greatly on environmental manipulations. Following the removal of V. vitis-idaea, E. nigrum generally increased branching, especially on open plots, and it increased the size of current shoots on open irrigated plots. However, when temperature was elevated, removal of V. vitis-idaea had negative effect on shoot growth and mass in E. nigrum. In V. vitis-idaea, current shoot size decreased after removal of E. nigrum on plots where either temperature or precipitation was increased. Only the most favourable conditions, on plots with both warming and watering, eliminated the negative effect of companion species removal on V. vitis-idaea. Acid rain treatment had no consistent effect on shoot growth of E. nigrum, while it greatly increased the production of adventitious shoots in V. vitis-idaea. The three years of experimental perturbations modified the shoot architecture markedly due to the effects of treatments on vegetative production per current shoot and the rate of lateral meristems activation. Changes in shoot architecture and phenology may be caused even by a short-term modification of climate and community composition, and may govern the success of these dwarf shrubs in a changing climate.

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