Performance of the LAI-2000 plant canopy analyzer in estimating leaf area index of some Scats pine stands PAULINE STENBERG, ’ SUNE LINDER, ’ HEIKKI SMOLANDER ” AND

Scats pine (Pinus sylvestris L.) in central Sweden at peak leaf area in August and after litterfall in October 1990. An independent estimate of leaf area index for August 1990 was obtained based on an empirically derived regression of needle area on stem sapwood area, and the decrease in leaf area between the two measurements was estimated from measurements of litterfall. A strong linear relationship was found between estimates by the LAI-2000 (LL’““‘) and the indirect estimates of leaf area index (taken as half of total surface area) (L). The finding that LLimCor was considerably smaller than L was explained theoretically. It was shown that if shoots, instead of individual needles, are randomly distributed in the canopy, LLImcor corresponds to L multiplied by a factor (p) characterizing the mutual shading of needles on the shoot. The shading factor, p, was equal to the ratio of spherically projected shoot area to spherically projected needle area, where the spherically projected area is defined as the average projection (silhouette) area taken over all directions in space. The quantity PL was defined as the shoot silhouette area index (SSAI), and an equation for the relationship between SSAI and the mean silhouette to total area ratio (STAR) of shoots was derived. Measured values of STAR for Scats pine indicated that LLimCor corresponds to SSAI rather than L. However, the decrease in leaf area index due to litterfall occurring between August and October was onl