Fig. 1.

(A) Locations of Populus nigra populations sampled in Spain (red), France (orange), the Netherlands (green), Germany (blue) and Italy (purple) for the common garden study. Abbreviations follow Table 1. (B) Principal components analysis of nine climatic variables (following Table 2) reveal heterogeneous environments at the 13 sampling locations. Red arrows and text indicate the loadings of each climate variable, while black text indicates the relative climate of each sampling site.