© 1994 Heron Publishing—Victoria, Canada
Performance of the LAI-2000 plant canopy analyzer in estimating leaf area index of some Scots pine stands
Pauline Stenberg (1), Sune Linder (2), Heikki Smolander (3) and Jeremy Flower-Ellis (2)
1. Department of Forest Ecology, P.O. Box 24, SF-00014 University of 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 September 24, 1993
Summary
The LAI-2000 plant canopy analyzer (Li-Cor, Inc., Lincoln, NE) was tested at six experimental plots of Scots 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 (LLi-Cor) and the indirect estimates of leaf area index (taken as half of total surface area) (L). The finding that LLi-Cor was considerably smaller than L was explained theoretically. It was shown that if shoots, instead of individual needles, are randomly distributed in the
canopy, LLi-Cor corresponds to L multiplied by a factor (β) characterizing the mutual shading of needles on the shoot. The shading factor, β, 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 βL 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 (mean STAR) of shoots was derived.
Measured values of mean STAR for Scots pine indicated that LLi-Cor corresponds to SSAI rather than L. However, the decrease in leaf area index due to litterfall occurring between August and October was only partly detected
by the LAI-2000, possibly because SSAI did not change to the same degree as L, i.e., there was an increase in the factor β. This hypothesis is supported by data showing a large increase in mean STAR
with shoot age.
Keywords:
canopy transmittance, shoot silhouette area index, STAR.
