The sapwood border was visually determined and marked in the field, immediately after core extraction, where the border between sapwood and heartwood can easily be recognized by differences in light transmittance. Since we intended to select sample trees covering the whole range of individual leaf area index (LAI = LA/APA)
in the stand, a first approximation of both, individual tree leaf area (LA) and the ground area potentially available (APA), were needed. For the first approximation of leaf area we assumed a strong relationship between sapwood area at breast height and leaf area (Eckmüllner and Sterba, 2000), and thus used sapwood area as a proxy for leaf area. While Assmann (1970) defined APA by the crown projection area of a tree plus a proportional part of the surrounding gaps (or DZNeP nmr minus the proportional overlaps with other trees), we used leaf area instead of crown projection area for defining APA, because leaf area is supposed to reflect the respective growing space more accurately (Assmann, 1970). Thus, Bcl-2 inhibitor we allotted the stand area to each tree proportionally to its leaf area. For the actual calculation of APA we used the procedure of Römisch (1995) with the square root of leaf area as a weight: the procedure starts with dividing the stand area into little squares of 1 dm2, and each
of these squares is then attributed to that tree for which D/LA is minimum, with D, the distance between the centre of the square and the position of the tree, and LA, the leaf area estimated from the sapwood area. Then, in order to select sample trees, the trees of each stand were split into 3 equally frequent classes of dbh, and each of the dbh-classes was further split into 3 classes (equal size) of leaf area index. In each of these 9 classes 3 trees were selected randomly, however, avoiding trees on the edge of the stand, trees with any kind of abnormal crown growth (e.g., signs of defoliation, broken tops), and those whose neighbours were one of the few Edoxaban broadleaf
trees in some of the stands. Thus, the sample size resulted in 27 sampled trees per stand. Since the two thinned and un-thinned pole stage stands, respectively were pooled for the selection of sample tress we finally had 162 sample trees. To estimate the leaf area of each sampled tree we calculated in a first step the dry needle mass of each sampled tree. In a second step, we used the strong relationship between dry weight of 100 needles and specific leaf area (SLA) according to Hager and Sterba (1985) to get the SLA of each tree. SLA refers to projected leaf area. The leaf area of each sampled tree could then be easily calculated by multiplying the SLA and the dry needle mass. The detailed procedure is described subsequently. Each of the 27 sample trees of a stand was felled and its crown was cut into three sections of equal length (where crown base was defined as the first live branch where no whorl with only dead braches was above) (Fig. 1).