Positive interactions between species are known to play an important role in the structure and dynamics of alpine plant communities. The balance between negative and positive interaction is known to shift along spatial and temporal gradients, with positive effects prevailing over negative ones as the environmental stress increases. Thus, this balance is likely to be affected by climate change. We hypothesized that increases of temperature (a global warming scenario) should decrease the importance of positive interactions for the survival and growth of alpine plant species. To test this hypothesis we selected individuals of the native species Hordeum comosum and the non-native species Taraxacum officinale and Cerastium arvense growing within the nurse cushion species Azorella madreporica at 3600 m.a.s.l., in Los Andes of Chile and performed nurse removal experiments under natural and warmer conditions. For warmer conditions we used open top chambers (OTCs), which increased temperature by 4°C. We compared the effect of nurse removal on the survival, biomass and photochemical efficiency of experimental individuals under warmer and natural conditions.
Results/Conclusions
Nurse removal significantly decreased the survival, biomass and photochemical efficiency of H. comosum and C. arvense demonstrating the facilitative effects of nurse cushions. T. officinale was not affected by nurse removal. Warmer conditions only partially mitigated the negative effects of nurse removal on the native species. While C. arvense did not showed evidence of facilitative effect by cushions under warmer conditions, T. officinale was facilitated by cushions under warmer conditions. While facilitative interactions will continue be important for the performance of some alpine species under future warmer conditions in high-alpine habitats, it might be not relevant for others. FONDECYT 1090389, F ICM P05-02, PFB-023.