O.D.C. 164.5:174.7--015
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METHODS OF MEASURING LEAF
SURFACE AREA OF SOME CONIFERS
by
H. Barker
Extrait en fraru;au
FORESTRY BRANCH
DEPARTMENTAL PUBLICATION No. 1219
1968
Published under the authority of the
Minister of Forestry and Rural Development
Ottawa, 1968
ROGER DUHAMEL, F.R.S.C.
QUEEN'S PRINTER AND CONTROLLER OF STATIONERY
OTTAWA, 1968
Cat. No.: Fo 47-1219
ABSTRACT
Two methods of determining the surface area of leaves of
several coniferous species were tested. One was based on a photoelectric principle where, by eliminating errors caused by differences in transmissiVity of material, accurate measurements were
obtained for the plane or projected leaf surface of Douglas-fir
(Pseudotsuga menziesii (Mirb.) Franco) and western hemlock (Tsuga
heterophylla (Raf.) Sarg.). The other was based on measurements
of the plane and the total leaf surface area. In the latter
method correction factors for longitudinal leaf curvature and
cross-sectional curvature were used. Satisfactory results were
obtained for Douglas-fir, western hemlock, Sitka spruce (Pice a
sitchensis (Bong.) Carr.), white spruce (Picea glauca (Moench)
Voss), and grand fir (Abies grandis (DougL) LindL). The product of the two correction factors remained constant within a
species from seedling to maturity.
EXTRAIT
L'auteur eprouve deux methodes pour mesurer la surface des
aiguilles de plusieurs coniferes. Avec l'une, il emploie Ie
principe qu'en photo-electricite, l'on peut eliminer les erreurs
causees par les differences dans la transmissibilite des materiaux, et ainsi toiser avec exactitude la projection sur un plan
des feuilles de Sapin Douglas (Pseudotsuga menziesii (Mirb.)
Franco) et de Pruche de l'Ouest (Tsuga heterophylla (Raf.) Sarg.).
Avec l'autre methode, il se base sur les dimensions mesurees
(largeur et longueur) des feuilles pour d'abord toiser la surface
de leur projection en plan puis leur surface totalej dans ce cas,
deux corrections sont necessaires: une premiere pour la courbure
longitudinale, et une seconde pour la courbure de la section
transversale. Se pretaient bien a cette methode Ie Sapin Douglas,
la Pruche de l'Ouest, l'Epinette de Sitka (Picea sitchensis (Bong.)
Carr.), l'Epinette blanche (Picea glauca (Moench) Voss) et Ie
Sapin grandissime (Abies grandis (Dougl.) Lindl.). Le produit obtenu par Ie facteur de correction demeure constant pour chaque
espece depuis sa naissance jusqu'a l'age murj ceci facilite de
beaucoup les calculs.
'Fi'.
w
•
METHODS OF MEASURING LEAF SURFACE AREA
OF SOME CONIFERS
by
H. Barker l
INTRODUCTION
Various means of measuring or estimating leaf areas have been
demonstrated. The photo-electric principle has been used extensively over a long period of time (Kramer 1937). Sources of error
in photo-electric methods, due to differences in light transmission
of foliage, are pointed out by Hurd and Rees (1966). Measurement
of leaf dimensions to determine area have been used by Baker (1948)
and Madgwick (1964). Estimations of area have been made through
correlation with weight (Cable 1958) and volume (Kozlowski and
Schumacher 1943). Small leaves make accurate measurements of leaf
area for most conifers difficult to obtain with normal laboratory
equipment. Some results of photosynthetic studies with Douglas-fir,
western hemlock, Sitka spruce and white spruce in this laboratory
prompted an investigation into methods that could be applied to
any of these species.
PHOTO·ELECTRIC MEASUREMENT
The objective was to determine the plane or projected surface
area of leaves by measuring the amount of light intercepted by the
leaves when placed between a light source and a light-measuring
instrument. For this purpose a photometer, having a selenium lightsensing probe and a scale graduated in foot-candles, was used. The
probe was factory equipped with a filter for reducing the incident
light by 20X. Since the probe varied slightly in sensitivity from
the centre to the edge, its outer edge was covered to give a uniformly sensitive surface of 3.0 cm diameter. The light source was
diffused and uniform over the probe surface.
To measure the plane surface of an opaque object, two scale
readings are made: one with the probe fully exposed to the light
and the other with the object placed on the face of the probe.
Using these two measurements, and the known area of the probe, the
surface area of the object can be calculated. Small objects should
be scattered uniformly over the probe face.
lResearch technician, Forest Research Laboratory, Department of
Forestry and Rural Development, Victoria, B.C.
1
The accuracy and linearity of response of the equipment was
tested, using opaque objects of known area. Consistent accuracy
was obtained only when the objects were slightly separated from
the probe. Thus all photometer measurements were made with the
probe face covered by a clear glass plate 1.5 mm thick supported
on the edges of the probe casing, giving a total separation of
3.0 mm. The thickness of the glass plate was important; errors of
+4.0% occurred when glass 2.5 mm thick was used.
When measuring areas of translucent objects, it is necessary
to make corrections for light transmitted through the objects.
This was done in two ways:
At a fixed light intensity, light was measured that passed
through an aperture 1.0 x 0.5 cm cut in an opaque cardboard plate.
The aperture was then covered with a single layer of leaves and a
further measurement taken. The percentage of light transmitted
through the leaves was the measure of their transmissivity. The
apparent surface area of the leaves was measured and corrected for
light transmittance to obtain the actual plane surface area.
Results were not consistent. This was attributed to inaccurate
measurements of transmittance, due to difficulty in covering the
aperture without gap or overlap of leaves. Obvious differences in
transmittance of leaves of different age and thickness could not
be detected.
In the second method the leaves were coated with a mixture of
black drawing ink and powdered detergent. Transmittance was
measured by first obtaining the apparent surface area of uncoated
leaves and comparing the result with that obtained when the same
leaves were coated. Thus measured, the transmittance of a representative sample could be used to correct the apparent surface
area of the whole sample.
Transmittance varied according to species, growing conditions,
and age of leaves. For example, when grown under controlled
environmental conditions, old Douglas-fir leaves had a transmittance of 10% and young leaves 16%. Transmittance for old and young
hemlock leaves was 16% and 27% respectively.
Photometer measurements of leaf areas obtained with this procedure agreed (± 1%) with areas calculated from linear measurements
of leaves cut in rectangular sections. The coating mixture can
easily be rinsed off in water.
The modified method for measuring light transmittance .was
satisfactory when applied to leaves of Douglas-fir and western he~
lock, and would probably be the same for other species that have
rather flat and straight leaves. For certain other foliage, such
as immature spruce leaves, some difficulty might be experienced in
handling, and greater errors could occur. This method gives only
the plane or projected surface of a leaf.
2
CALCULATION FROM LEAF DIMENSIONS
The plane and the total surface areas of leaves were obtained
from measurements of leaf dimensions. Length and width were
measured and corrections made for the curvature of the leaves. For
the plane surface area, leaf length times width was corrected for
the longitudinal leaf curvature. To obtain the total leaf surface,
an additional correction for the cross-sectional curvature was made.
The effect of plant age and growing conditions on the correction
factors was investigated using a Bausch and Lomb micro-slide projector and a K & E polar planimeter.
The plane surface of a leaf was projected at a magnification
of lOX and the outline traced on a sheet of graph paper. The area
within this outline was measured by a planimeter. This area,
divided by the area calculated from measurement of the projected
leaf length and width at mid-point, gave the plane surface correction factor (f1)'
Figure 1. Method of projecting leaf outlines
for measurement. Cross-sections of
Abies grandis 'leaves at 40X.
3
Thin cross-sections of the same leaf were made, one each at
the tip, mid-point, and base; those at the tip and basal sections
were made at the mid-portion of the leaf taper. The cross-sections
were projected at a magnification of 40X (Figure 1) and their outlines traced. The measured perimeter of each section outline was
divided by its width to obtain a cross-section factor. Each factor
was weighed by the length of the leaf portion it represented to
obtain a mean cross-sectional correction factor (f 2 ).
There was a consistent inverse relationship between the
factors f 1 and f 2 • Comparison of leaves within a species at different stages of growth and grown under different conditions, and,
to a certain extent, of leaves within a sample, showed that when
the factor f1 was lower or higher than the mean for the species or
sample, the factor f 2 was correspondingly higher or lower (Table 1).
Thus the product of the factors tended to be a constant (K) for
each species.
Samples used were normal leaves of current growth selected at
random from 6 to 10 branches or plants. Growing conditions varied
from controlled environment in growth room or greenhouse for seedlings, to field-grown immature and mature trees.
The statistical significance of the results was analyzed by
the t-test, and the 95% confidence limit of the measurements is
indicated in Table 1.
4
Table 1. Correction factors for determining plane and total leaf
surface area from measurements of leaf length and width.
Species
Longit udinal
correction
Factor
f
I
X
I
Cross-sectional
=
correction
Factor
0.776
0.900
0.899
0.894
K
f2
1
2.75
2.32
2.35
2.37
13.0
4.0
5.1
7.2
10.8
5.1
4.7
4.0
Average all leaves
Western hemlock
cotyledons
seedlings
young trees
mature trees
0.822
0.875
0.847
0.861
2.27
2.16
2.20
2.21
7.0
1.7
4.5
5.7
7.0
3.8
4.1
3.7
Average all leaves
Sitka spruce
cotyledons*
seedlings
young trees
mature trees
0.788
0.823
0.877
0.930
2.85
2.76
2.59
2.44
6.5
3.6
3.6
6.4
3.0
3.8
Average all leaves
White spruce
cotyledons
seedlings
young trees
mature trees
0.855
0.825
0.907
2.91
3.04
2.78
7.4
5.0
15.0
11.0
9.6
17.0
Average all leaves
Grand fir
young trees
mature trees
0.885
0.890
±%
±%
±%
Douglas fir
cotyledons
seedlings
young trees
mature trees
Total surface
correction
Factor
2.32
2.31
3.5
2.5
*Insufficient data.
5
3.5
4.3
2.13
2.09
2.11
2.12
5.7
6.4
4.8
5.5
2.106
5.3
1.87
1. 89
1.86
1.90
6.0
4.0
3.5
3.7
1.893
5.0
2.25
2.27
2.27
2.27
5.5
3.6
2.5
2.267
3.8
2.49
2.51
2.52
5.2
2.5
2.7
2.502
1.8
2.05
2.06
1.5
2.2
REFERENCES
Baker, F.S. 1948. A short method of determining leaf area and
volume growth in pine trees. Hilgardia 18: No.8.
Cable, D.R. 1958. Estimating surface area of ponderosa pine
foliage in central Arizona. Forest. Sci. 4:45-49.
Hurd, R.G., and A.A. Rees. 1966. Transmission errors in the
photometric estimation of leaf area. Plant Physiol.
41:905-906.
Kozlowski, T.T., and F.X. Schumacher. 1943. Estimation of
stomated foliar surface of pines. Plant Physiol. 18:122-127.
Kramer, P.J. 1937. An improved photo-electric apparatus for
measuring leaf areas. Amer. J. Bot. 24:375-376.
Madgwick, H.A.I. 1964. Estimation of surface area of pine
needles with special reference to pinus resinosa. J. Forest.
62: 636.
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