© 1994 Heron Publishing—Victoria, Canada
Dependence of light interception efficiency of Scots pine shoots on structural parameters
H. Smolander (1), P. Stenberg (2) and S. Linder (3)
1. The Finnish Forest Research Institute, Suonenjoki Research Station, SF-77600 Suonenjoki, Finland / 2. Department of Forest Ecology, P.O. Box 24, SF-00014 University of Helsinki, Finland / 3. Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences, P.O. Box 7072, S-750 07 Uppsala,
Sweden / Received September 24, 1993
Summary
The ratio of shoot silhouette area to total needle area (STAR) is one means of quantifying the light interception efficiency
of a coniferous shoot. The silhouette area (or STAR) of a shoot depends on various structural characteristics of the shoot,
and also varies with the direction of the shoot relative to the direction of radiation (sun angle). The mean STAR taken over
all directions in space is the mean ratio of shoot silhouette area to total needle area in an isotropic radiation field. It
also represents a mean STAR with respect to a spherical shoot orientation.
In this study, equations for the relationship between mean STAR and easily measurable shoot characteristics were developed.
The STAR values in different directions were determined from photographically measured shoot silhouette areas. Mean STAR varied
between 0.079 and 0.308, and averaged 0.146. A clear increase in mean STAR with age was found. The material consisted of 305
Scots pine (Pinus sylvestris L.) shoots from Sweden and Finland, representing shoots of different age and a wide variation in site fertility. The needle
area density in the shoot cylinder, together with the diameters of the shoot cylinder and the twig explained 87% of the variation
in mean STAR.
Keywords:
canopy structure, Pinus sylvestris, shoot structure, STAR.
