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Dryad

Physiological tolerance to frost and drought explains range limits of 35 European tree species

Baranger, Anne1; Cordonnier, Thomas2; Charrier, Guillaume1; Delzon, Sylvain1; Larter, Maximilian1; Martin-StPaul, Nicolas1; Kunstler, Georges1

Published Nov 22, 2024 on Dryad. https://doi.org/10.5061/dryad.547d7wmh1

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Abstract

Models are key to evaluating how climate change threatens European forests and tree species distributions. However, current species distribution models struggle to integrate ecophysiological processes. Mechanistic models are complex and have high parameter requirements. Some correlative species distribution models have tried to include traits but so far have failed to directly connect to ecophysiological processes. Here, we propose an intermediate strategy where species distributions are based on their safety margins which represent their proximity to their physiological thresholds.

We derived frost and drought safety margins for 38 European tree species as the difference between physiological tolerance traits and local maximum stress. We used LT50 and P50 as tolerance traits for frost and drought, respectively, and local minimum temperature and minimum soil water potential as maximum stress. We integrated these safety margins into a species distribution model, which tests if the probability of species presence declines rapidly when the safety margin reaches zero, when physiological stress exceeds the species' tolerance traits.

Our results showed that 35 of the 38 studied species had their distribution explained by one or both safety margins. We demonstrated that safety-margins-based model can be efficiently transferred to species for which occurrence data are not available.

The probability of presence dropped dramatically when the frost safety margin reached zero, whereas it was less sensitive to the drought safety margin. This differential sensitivity may be due to the more complex regulation of drought stress, especially as water is a shared resource, whereas frost is not. However, we did not find a clear effect of local competition hierarchy on the response to safety margin, but competition needs further analysis.

Our analysis provides a new approach to linking species distributions to their physiological limits and shows that, in Europe, frost and drought safety margins are important determinants of species distributions.