The responses of ecosystems to climate change are expected to depend on both directional changes in the average climate (gradual climate change) and an increase in the frequency of extreme climatic events. However, we know little about how extreme events combine with gradual climate change to shape these impacts. Gradual climate change could condition ecological communities though adaptive processes, strengthening them to resist extreme events. Alternatively, gradual climate change might push ecosystems towards tipping points, facilitating regime shifts.
We examined the impacts of an extreme natural drought on a species-rich grassland subjected to 25 years of experimental climate change at the Buxton Climate Change Impacts Lab (BCCIL). Adaptive processes, including trait-mediated shifts in species abundance, and intraspecific evolutionary adaptation are known to have buffered this grassland community from the effects of climate manipulations. We assessed the cover of vascular plant species in 240 permanent quadrats located in the grassland plots, in 2019, the year after an extreme natural drought. We combined these data with data from identical surveys conducted in 2008, 2012 and 2016. We hypothesised that gradual climate change—the experimental treatments—would buffer the plant community from the effects of the natural extreme drought.
Results/Conclusions
Contrary to our expectation, preceding experimental climate change did not buffer the grassland against natural drought. Instead, species turnover and net losses of species richness increased in the survey interval in which the natural drought had occurred, relative to all other survey intervals. We analyse the patterns of species losses and gains occurring in different experimental treatments during the extreme drought, and the relationships of these responses to species’ functional traits. We use these results to propose a model for the joint impacts of gradual climate change and extreme drought on grassland vegetation.