Simulated climate change altered dominance hierarchies and diversity of an alpine biodiversity hotspot

Alpine and arctic ecosystems may be particularly vulnerable to climate change. We know little about alpine plant community responses to the predicted abiotic changes, or to possible changes in the biotic environment caused by climate change. Four years of experimental warming and nutrient addition altered dominance hierarchies, community structure, and diversity of an alpine biodiversity hotspot in south Norway. The previously dominant dwarf shrub Dryas octopetala was replaced by graminoids and forbs under nutrient addition and warming with nutrients. Community diversity declined due to decreased bryophyte and lichen richness and abundances, and dwarf shrub abundances. In controls and in plots with only warming, where Dryas maintained dominance, the relationships between changes in Dryas cover and changes in community parameters were negative, suggesting that Dryas controls community processes. Under nutrient addition, bryophyte and lichen diversity decreased with decreasing Dryas cover, probably due to increased competition from graminoids and forbs. The shift in dominance hierarchies changed community structure and dynamics through increased biomass, vegetation height, and competition for light. Community diversity dropped primarily because changes in the abiotic environment modified biotic interactions, highlighting that species interaction must be considered in climate change experiments and in models predicting climate change effects.