IntroductionIs global warming only about extremely warm events?
In April 2017, cold air from the Arctic penetrated western Europe following an unprecedented warm period that had induced vegetation to spring out. This frost event caused severe damage to natural and cultivated plants, which altogether led to an estimated 3.3 billion euros of economic loss. Furthermore, the reduced photosynthesis resulting from leaf damage contributed to an increase of atmospheric CO2.
Altogether, the burden these late-spring cold snaps will represent for vegetation and carbon cycling still needs to be explored.
Our study analyzes the change in late-spring frost events over nearly 60 years, their geographic distribution, and the resistance strategies plants have developed to avoid damage. Pairing annual frost occurrences and plant characteristics at the global scale allows us to forecast the vulnerability of forests to late frost events under climate change.
MethodMapping of spring frost and leaf-out strategies
Then, we analyzed plant-traits of 1,500 temperate and boreal woody species cultivated in botanical gardens, and identified where they naturally occur within over 530,000 forest and shrubland locations around the world. Using these data, we mapped the distribution of vegetation according to their leaf-out strategies (“cautious” vs. “opportunistic”) and leaf frost susceptibility. We were then able to test the correlation between the distribution of late-spring frost and plant strategies.
Finally, we projected the future distribution of late-spring frost using the trend of extreme events over the past 60 years. Crossing these data with plant-traits allows us to forecast forest vulnerability under climate change.
ResultsGeographic distribution of late-spring frosts
Our results also show that, at the continental scale, the incidence of late-spring frost events decreases with higher latitude, where temperatures are more consistently cold. However, their frequency increases with distance to the sea or higher elevation, most likely due to more variable daily temperatures.
ResultsDistribution of “cautious” vs “opportunistic” trees
We further show that in cold, high latitude regions, trees have evolved freeze-resistant leaves. In contrast, in lower latitudes, where late-spring frost risk is high, leaves are more susceptible to frost, implying negative consequences if climate change will lead to more frequent frost occurrences.
Altogether, the geographic distribution of “cautious” vs “opportunistic” species reflects the historical occurrence of late-spring frost events: more “cautious” species in North America and more “opportunistic” species in Europe and Asia.