European plants lagging behind climate change pay a climatic debt in the North, but are favoured in the South.

ABSTRACT

For many species, climate change leads to range shifts that are detectable, but often insufficient to track historical climatic conditions. These lags of species range shifts behind climatic conditions are often coined "climatic debts", but the demographic costs entailed by the word "debt" have not been demonstrated. Here, we used opportunistic distribution data for c. 4000 European plant species to estimate the temporal shifts in climatic conditions experienced by these species and their occupancy trends, over the last 65 years. The resulting negative relationship observed between these two variables provides the first piece of evidence that European plants are already paying a climatic debt in Alpine, Atlantic and Boreal regions. In contrast, plants appear to benefit from a surprising "climatic bonus" in the Mediterranean. We also find that among multiple pressures faced by plants, climate change is now on par with other known drivers of occupancy trends, including eutrophication and urbanisation.