The relative importance of neighbours and abiotic environmental conditions for population dynamic parameters of two alpine plant species

1 Vegetation removal manipulations over four growing seasons in an alpine Dryas heath at Finse, south Norway, were used to examine the role of neighbour vegetation in the population dynamics of the forb Thalictrum alpinum and the sedge Carex vaginata. We also increased temperature (by open top chambers) and nutrient availability to assess if effects of surrounding vegetation may be modified by environmental change. 2 Removal of neighbour vegetation increased the number of leaves of Thalictrum and Carex, whereas flowering stems and leaf stalks of Thalictrum became significantly shorter. Furthermore, increased plant growth after nutrient addition and warming suggests that both abiotic environmental conditions and biotic interactions limit plant growth at Finse. 3 Our results suggest that there is competition for nutrients at Finse, but that surrounding vegetation may also have facilitative sheltering effects on other species. 4 Interactions between vegetation removal and abiotic factors on population dynamic parameters of Thalictrum suggest that plant-plant interactions may be modified if temperature and nutrient availability increase under climate change. 5 The responses of the two target species to the removal of the general neighbour vegetation were less pronounced than their responses to the removal of the dominant Dryas octopetala examined in a previous study. This suggests that one dominant species may affect the population dynamics of other species more than the net effect of all the other species in the community in concert. 6 Our results show that biotic interactions may affect alpine plant populations and thereby structure alpine plant communities. Furthermore, the effects of neighbours and abiotic environmental changes on alpine plant growth may depend on the species identity of the neighbours.