© 1995 Heron Publishing—Victoria, Canada
Variation in the ratio of shoot silhouette area to needle area in fertilized and unfertilized Norway spruce trees
Pauline Stenberg (1), Sune Linder (2) and Heikki Smolander (3)
1. Department of Forest Ecology, P.O. Box 24, University of Helsinki, SF-00014 Helsinki, Finland / 2. Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences, P.O. Box 7072, S-750 07 Uppsala,
Sweden / 3. The Finnish Forest Research Institute, Suonenjoki Research Station, SF-77600 Suonenjoki, Finland / Received November 17, 1994
Summary
We compared the range and variation in shoot silhouette area to projected leaf area ratio (SPAR) in fertilized and unfertilized
(control) Norway spruce (Picea abies (L.) Karst.) trees. We measured SPAR for several 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 control 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 with
inclination and rotation angle of the shoot (relative to the view direction). 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 (SPARmax).
Differences in SPAR between fertilized and control trees were explained by changes in shoot structure in response to fertilization
and shading. Shoots of fertilized trees were larger and had more needle area than shoots of control trees. However, the ratio
of needle area to shoot size was smaller in fertilized trees than in control trees, implying less within-shoot shading and,
consequently, a larger SPAR. Also, the increase in SPAR with increased shading (depth in the crown) could be explained by
a decrease in the ratio of needle area to shoot size. In addition, because fertilized trees had more needle area than control
trees, the effect of shading at a given depth in the crown was more pronounced in fertilized trees than in control trees.
Keywords:
fertilization, light interception efficiency, Picea abies, shading, shoot structure, SPAR, STAR.
