Evolution across the chronosequence of the vertical structure indices in Valsaín (dots) and Navafría (continuous line): (a) Shannon’s index H′; (b) structure index based on the sum of square roots of differences in tree heights SQRI; (c) Gadow’s index for height and 3 neighbours DH3; (d) structure complexity index, SCI; (e) structure index based on the variance of tree height, STVI.