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The genetic nature of tree adaptation to drought stress was examined by utilizing variation in the drought response of a full‐sib second generation (F₂) mapping population from a cross between Populus trichocarpa (93‐968) and P. deltoides Bart (ILL‐129) and known to be highly divergent for a vast range of phenotypic traits. We combined phenotyping, quantitative trait loci (QTL) analysis and microarray experiments to demonstrate that ‘genetical genomics’ can be used to provide information on adaptation at the species level. The grandparents and F₂ population were subjected to soil drying, and contrasting responses to drought across genotypes, including leaf coloration, expansion and abscission, were observed, and QTL for these traits mapped. A subset of extreme genotypes exhibiting extreme sensitivity and insensitivity to drought on the basis of leaf abscission were defined, and microarray experiments …