2.5. Leaf morphological characteristics of birch
Since shade is known to influence specific leaf area (SLA;
Wuytack et al., 2011) we collected birch leaves from different
branches of the sun crown in the end of July 2010 when leaves were
fully developed and not yet affected by senescence. Nine to 20
leaves per tree (N ¼ 95) at each location (N ¼ 38) were used in a
mixed sample to characterize site conditions, resulting in total
N ¼ 1119 leaves. A site consists of one to four trees which are
located in the nearest proximity and are subjected to equivalent
environmental conditions. Coarse particles adhered to the leaves
were washed off using demineralized water. We weighted each
leave and measured the thickness with a thickness tester. Leaf area
was analytically determined from scanning. The specific leaf area
(SLA) was calculated as the ratio of leaf area to leaf mass in cm2/g.