Environmental variable Abbr. Description Temporal range Resolution Source
Climate Growing degree days GDD Annual sum of degree-days over a 0°C soil temperature Average across 2009-2019 Plot SAFRAN- SURFEX/ISBA-Crocus-MEPRA reanalysis (Vernay et al. 2021)
Annual precipitation AP The sum of all the monthly precipitation estimates
Frost degree days FDD Annual sum of average daily degrees below zero in soil temperature. Summarizes the duration and intensity of ground freezing events.
Soil Soil pH pH Top-soil wahter pH Same year than the sample was collected (2016-2020) Sample Measured in the lab
Soil Organic Matter SOM Soil organic matter content Sample
Soil C/N C/N Soil carbon to nitrogen ration in organic matter Sample
Vegetation Plant taxonomic dissimilarity Jaccard pairwise dissimilarity index between subplots. Same year than the sample was collected (2016-2020) Plot Botanical surveys
Plant functional dissimilarity
Jaccard-like functional index. Traits: specific leaf area (SLA), leaf C/N, root depth (ordered variable), vegetative plant height, and woodyness index (categorical variable ranging from herbaceous to woody).
Plot
Botanical surveys and our own trait measurement values for species (median values across individuals). Root depth was , extracted from (Landolt et al. 2010).
Normalized Difference Vegetation Index NDVI Estimated from the surface spectral reflectance at a resolution of 250 m. Raw NDVI times series were pre-processed following (Choler 2015), and we kept the mean yearly sum of NDVI greater than 0.2 Average across 2010-2020 Plot MODIS (Moderate Resolution Imaging Spectroradiometer), available online: https://lpdaac.usgs.gov/produ cts/mod09q1v006/.