Total height growth after two growing seasons (H2) was affected by both site and seed source effects (Table 2). However, the interaction between the two factors was not significant, suggesting that the two seed sources showed similar patterns of growth in response to changes in growing conditions along the climatic gradient (Table 2). The highest and lowest average of H2 were observed at the Dorion (76 ± 11 cm) and Deville (51 ± 7 cm) sites, respectively (Fig. 2). Seedlings from the southern seed source were significantly taller than those from the northern seed source (Fig. 2). No statistically significant relationships could be found between H2 and prevailing climatic and soil conditions at the plantation sites (Supplementary Data Fig. S1).