Agricultural and Forest Meteorology 100 (2000) 255–260
Assessing bias from boles in calculating leaf area index in immature
Douglas-ﬁr with the LI-COR canopy analyzer
, J.A. Trofymow, R.I. Leach
Paciﬁc Forestry Centre, 506 West Burnside Road, Victoria, BC, Canada, V8Z 1M5
Received 26 April 1999; accepted 3 September 1999
Measurementsofleafareaindex (LAI)taken withphotometers such asthe LAI2000 arebiased by bolesand branches which
stop part of the light from reaching the photometer. We estimated how much of the sky would be obscurred by boles in an
immature stand of Douglas-ﬁr (Pseudotsuga menziesii (Mirb) Franco) that was stem-mapped and of known diameter, height
and height-to-live-crown. These yielded gap fractions which were then converted to bole area index (BAI) via the algorithm
used by the LAI2000. The mean BAI, as a fraction of the effective leaf area index (LAIe) calculated by the LAI2000, ranged
from <0.01 for Douglas-ﬁr at 24 years of age to about 0.1 at 48 years. Comparing readings on Douglas-ﬁr trees defoliated by
root rot with readings on fully foliated trees yielded a proportion of 0.41, which included branches. Measurements were also
taken on clumps of maple (Acer macrophyllum Pursh) and alder (Alnus rubra Bong.) both before and after leaf-fall, yielding
corresponding proportions, including branches, of 0.41 and 0.25, respectively. The values obtained this way are probably
upper limits. The contributions of boles may be appreciable, particularly in mature unthinnned stands with closed canopies.
©2000 Elsevier Science B.V. All rights reserved.
Keywords: Leaf area index; LAI-2000; Douglas-ﬁr
Leaf area index (LAI- one half total leaf area per
unit ground surface area (m
)) can be assessed in-
directly with the LI-COR LAI-2000 Plant Canopy An-
alyzer (Deblonde and Penner, 1994). However, these
estimates are biased by blockage of light by boles and
branches and, in conifer stands, also by non-random
distribution of foliage elements. The output of the
LAI-2000 analyzer is thus an effective leaf area index
Corresponding author. Tel.:+1-250-363-0736;
E-mail address: email@example.com (H.J. Barclay).
(LAIe) rather than a LAI (Chen and Black, 1992). It
would thus, be useful to quantify the contributions of
the woody parts to the calculation of LAIe.
LAIe is related to LAI according to the equation
(1 − α) LAIe
where α is the ratio of woody surface area to total
surface area; γ
is the shoot clumping factor;
the clumping index quantifying the effect of foliage
clumping at larger scales than the shoot, and γ
is the total stand clumping index () and equals unity
when foliage distribution is random.
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