Sampling locations of mapping population. Highlighted by red full circles are sampling locations of American beech full-sib individuals used for association mapping study across stands in six U.S. states and two Canadian provinces. The map graphic was reproduced in the package ‘ggmap’ (Spatial visualization in ggplot2) v.2.6.1 (Kahle and Wickham)  in software R with Google Maps and Stamen Maps. For Fig. 1 a copyright permission was not required