Effects of experimental climate warming and associated soil drought on the competition between three highly invasive West European alien plant species and native counterparts

It is widely suggested that climate warming will increase the impact of biological invasions, yet, to date studies on the combined effect of these two global changes are scarce. Here, we study how climate warming and associated soil drought affect the competition between native and invasive alien plant species. Three highly invasive alien plant species in West Europe, each with a native competitor, were grown either together or in isolation at ambient and at elevated air temperature (+3 °C) in climate-controlled chambers. Equal amounts of water were added to all communities. Soil drought observed in the heated chambers did not induce severe stress in the plants. In two species pairs, Fallopia japonica (Houtt.)–Cirsium arvense (L.) Scop. and Solidago gigantea Ait.–Epilobium hirsutum L. (alien invasive–native), the native species dominated in mixture, while the alien invasive species dominated in the third pair Senecio inaequidens DC.–Plantago lanceolata L. Warming did not modify the competitive balance in any of these pairs, in spite of enhancing the aboveground biomass of S. inaequidens and P. lanceolata and the greater photosynthetic rates in S. inaequidens. The results of this study cannot be extrapolated to all invasive or exotic species but may represent the possible future of three principle invaders and some of their key native counterparts. Future experiments are needed to identify response patterns of alien plants to climate warming more in general.