DEPENDENCE OF LIGHT INTERCEPTION EFFICIENCY OF SCOTS PINE SHOOTS ON STRUCTURAL PARAMETERS

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 st ructural characteristics of the shoot, and also varies with the direct ion of the shoot relative to the direction of radiation (sun angle). T he mean STAR (STAR) taken over all directions in space is the mean rat io of shoot silhouette area to total needle area in an isotropic radia tion field. It also represents a mean STAR with respect to a spherical shoot orientation. In this study, equations for the relationship betw een STAR and easily measurable shoot characteristics were developed. T he STAR values in different directions were determined from photograph ically measured shoot silhouette areas. STAR varied between 0.079 and 0.308, and averaged 0.146. A clear increase in STAR with age was found . The material consisted of 305 Scots pine (Pinus sylvestris L.) shoot s 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 t wig explained 87% of the variation in STAR.