Fig. 5

Tree-ring width chronologies obtained for the five P. nigra study sites and related January SPEI drought index (calculated at 8-month scale) for the twentieth century. The plotted drought index was the most strongly related to annual tree-ring width indices in four out of five study sites (see tree-ring width–SPEI Pearson correlation coefficients and related probability levels in each plot in Fig. 4). Sites’ codes are as in Table 1