Environmental variables
At each site, spatial geographical coordinates and altitudes were
recorded using a handheld GPS (eTrex Venture, Garmin, Olathe, Kansas,
USA). Climate attributes, including mean annual temperature (MAT) and
precipitation (MAP) of each sampling site were obtained from the global
climate data set WorldClim 2.0 (1-km spatial resolution) (Fick &
Hijmans 2017). Total N concentration of soil samples was determined
using wet oxidation and a modified Kjeldahl procedure, and total P
concentration was measured by colorimetric analysis with ammonium
molybdate and persulfate oxidation (Murphy & Riley 1962). Thus, our
environmental predictors included MAP, MAT, altitude, soil N, and soil
P.