VARIATION IN THE RATIO OF SHOOT SILHOUETTE AREA TO NEEDLE AREA IN FERTILIZED AND UNFERTILIZED NORWAY SPRUCE TREES

We compared the range and variation in shoot silhouette area to projec ted leaf area ratio (SPAR) in fertilized and unfertilized (control) No rway spruce (Picea abies (L.) Karst.) trees. We measured SPAR for seve ral view directions of 169 shoots at different depths in the crown of fertilized and control trees. There was an increase in SPAR with depth in the crown in both central and fertilized trees. In the fertilized trees, however, mean SPAR was larger overall, the increase with depth in the crown was steeper, and there was a larger variation in SPAR wit h inclination and rotation angle of the shoot (relative to the view di rection). In particular, shoots in the lower crown of fertilized trees were rotationally asymmetrical (''flat'') and had high values of the maximum ratio of shoot silhouette area to projected leaf area (SPAR(ma x)). Differences in SPAR between fertilized and control trees were exp lained by changes in shoot structure in response to fertilization and shading. Shoots of fertilized trees were larger and had more needle ar ea than shoots of control trees. However, the ratio of needle area to shoot size was smaller in fertilized trees than in control trees, impl ying less within-shoot shading and, consequently, a larger SPAR. Also, the increase in SPAR with increased shading (depth in the crown) coul d be explained by a decrease in the ratio of needle area to shoot size . In addition, because fertilized trees had more needle area than cont rol trees, the effect of shading at a given depth in the crown was mor e pronounced in fertilized trees than in control trees.