Temperature data
We combined the Rallarvägen 2021 dataset with soil temperature estimates
from the ‘Global maps of soil temperature’, which provides global
modeled soil temperatures averaged for the period 1979-2013 at a spatial
resolution of 1 km² for 0-5 cm depth (SoilTemp; Lembrechts et al. 2021).
These maps were constructed by calculating differences (i.e., offsets)
between in situ soil temperature time series from over 1,200
1-km² pixels, summarized from 8,500 unique temperature sensors across
all the world’s major terrestrial biomes, and coarse-grained air
temperature estimates from ERA5-Land (Lembrechts et al. 2020). ERA5-Land
provides a reanalysis dataset with monthly free-air temperatures at a
spatial resolution of 0.1 x 0.1 degrees (Copernicus Climate Change
Service (C3S), 2019). We used the mean annual soil temperature (SBIO1),
mean soil temperature of the warmest quarter (SBIO10; hereafter named
Mean Summer Soil Temperature (MSST)), and mean soil temperature of the
coldest quarter (SBIO11). We extracted temperatures for each transect
using the extract function from the raster package in R (Hijmans,
2021).