Recovery of plant species diversity during long-term experimental warming of a species-rich alpine meadow community on the Qinghai-Tibet plateau

Climate change is predicted to dramatically alter the composition of plant communities. The impact of climate change on these communities is often based on short-term warming experiments, which have revealed marked declines in species diversity in response to relatively minor increases in average annual temperatures. The long-term effects of such warming on community diversity and composition, however, are less well understood. Here, we formalize a hypothesis of rebounding diversity, where species richness initially declines in response to warming, but subsequently recovers through a combination of colonization (via dispersal and seed banks) and competitive release (via shifts in the dominant species). We compared long-term changes in species diversity and abundance between control and experimentally warmed (1–2 °C) plots, sampled over an 18-year period, in alpine meadow communities of the Qinghai-Tibet plateau. While there was an initial decline in species diversity by c. 40% (11–19 species) over the first four years, 18 years later, diversity had rebounded to initial levels, on a par with control plots. The composition of the experimentally warmed communities, however, was significantly altered. Our study suggests that short-term experiments may be insufficient to capture the temporal variability in community diversity and composition in response to climate change. Rather, the long-term impacts of continued global warming are predicted to result in highly dynamic processes of community reassembly and turnover that do not necessarily lead to a net decline in local diversity, but do lead to the formation of novel communities.