Number of samples (n), frequency (in% of the total number of samples) and surface (in % of the total surface) occupied by World Reference Base (WRB) major soil groups [30].

aPercentage of the total surface occupied WRB major soil groups. Data should be considered approximate: surfaces have been computed using the dominant value of the soil typological units of the European Soil Database [58]. The total land surface considered is the European continent and islands (United Kingdom, Ireland, Iceland, Malta, Sicily, Sardinia, Corsica,…), excluding Russia and Turkey.