DOI: 10.5061/dryad.547d7wmh1
title: Physiological tolerance to frost and drought explains range limits of 35 European tree species

description: 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.
description: # Physiological tolerance to frost and drought explains range limits of 35
 European tree species
 [https://doi.org/10.5061/dryad.547d7wmh1](https://doi.org/10.5061/dryad.547d7wmh1) This repository provides the data and code required to compute safety margins of 38 tree species across Europe. The code enables us to fit distribution models based on these safety margins, and to compute performance metrics of models. ## Description of the data `Trait_ecog_filtered_dryad.csv` gathers stress tolerance traits used in the analysis, for the 38 European species. This database results from the aggregation of data from a literature review. "class", "order", "family", "genus" and "taxa" are phylogenetic information. "lt50" and "lt50sd" are the raw mean, and standard deviation of frost resistance computed from the literature review. "lt50source" indicates on which anatomical structure the frost resistance was measured. P12, P50, and P88 are the measures of tree resistance to cavitation, and P50sd is its standard deviation. "px" is the final value chosen among P50 and P88 for the species. "pxsource" indicates from which database the trait was extracted. "slope" and "slopemsp" are measures of the slopes of the vulnerability curves. `era5_svwcperc05d_X_1984-2021_inv` files (with X being h1, h2, h3 or h4), are the minimum soil water content computed over the four soil horizons across Europe. Each layer was derived from monthly data obtained from ERA5-land climate reanalysis accessible at [https://cds.climate.copernicus.eu/datasets/reanalysis-era5-land?tab=download](https://cds.climate.copernicus.eu/datasets/reanalysis-era5-land?tab=download) `era5_t2min05_1984-2021.grib` is the minimum temperature. It is also derived from ERA5-land reanalysis. ## Access to other required data Other data needs to be downloaded to run the analysis. ### Hydraulic parameters Hydraulic parameters of soil layers can be downloaded from EU_SoilHydroGrids [database](https://esdac.jrc.ec.europa.eu/content/3d-soil-hydraulic-database-europe-1-km-and-250-m-resolution). ### Rooting depth Soil rooting depth can be downloaded from the [European Soil DataBase](https://esdac.jrc.ec.europa.eu/content/european-soil-database-derived-data) ### Mean climate variables Mean annual temperature (bio1), mean annual precipitation (bio12), growing degree days (gdd5) and potential evapotranspiration (pet_penman) were download from [CHELSA](https://envicloud.wsl.ch/#/?bucket=https%3A%2F%2Fos.zhdk.cloud.switch.ch%2Fchelsav2%2F&prefix=%2F) over the period 1981-2010. ### Species occurrence We used EuForest data from [Mauri et al. (2017)](https://www.nature.com/articles/sdata2016123) to get occurrence data of our 38 tree species. ### Species distribution expert maps The analysis requires maps of species distribution from expert-knowledge. These were download from the EuForgen project at [this path.](https://doi.org/10.1016/j.dib.2017.05.007) ### Biomes map Map of global biomes can be downloaded from [WWF website](https://www.worldwildlife.org/publications/terrestrial-ecoregions-of-the-world). ## Description of the code The main worflow is written with the targets package, and all you need to do is run the tar_make() function in R. The workflow functions are written in separate R files. Finally, a figure file is used to load objects and create figures. The whole workflow takes quite a long time to complete. .stan files are the files of the different models run during the analysis. ## Data folder architecture To run the whole code, we suggest users to reproduce the same arborescence as we used in our analysis, which implies a data folder with the following organisation: \- ERA5-land \-- daily \---era5_svwcperc05d_h1_1984-2021_inv \---era5_svwcperc05d_h2_1984-2021_inv \---era5_svwcperc05d_h3_1984-2021_inv \---era5_svwcperc05d_h4_1984-2021_inv \--t2m \---era5_t2min05_1984-2021.grib \- CHELSA (files to download as describe above) \-- Bio1 file \-- Bio12 file \-- Gdd5 file \-- Pet_penman file \- species trait \-- base_traits_P50_LTx.xlsx \- STU_EU_Layers (*files to download as describe above in* **Rooting depth**) \-- soil rooting depth file \- EU_SoilHydroGrids_1km *(files to download as describe above in* **Hydraulic parameters**) \-- all hydraulic parameters files \- WWF (*files to download as describe above in* **Biomes map**) \-- official \--- all files downloaded \- chronologica_maps_dataset (*files to download as describe above in* **Species distribution expert maps**) \-- all file downloaded \- EUForestsMauri (*files to download as describe above in* **Species occurrence** ) \--all files downloaded