HAL Id: hal-00883553
https://hal.archives-ouvertes.fr/hal-00883553
Submitted on 1 Jan 2010
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entic research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diusion de documents
scientiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
Wood colour variation in sapwood and heartwood of
young trees of Tectona grandis and its relationship with
plantation characteristics, site, and decay resistance
Róger Moya, Alexander Berrocal
To cite this version:
Róger Moya, Alexander Berrocal. Wood colour variation in sapwood and heartwood of young trees of
Tectona grandis and its relationship with plantation characteristics, site, and decay resistance. Annals
of Forest Science, Springer Nature (since 2011)/EDP Science (until 2010), 2010, 67 (1), �10.1051/for-
est/2009088�. �hal-00883553�
Ann. For. Sci. 67 (2010) 109 Available online at:
c
INRA, EDP Sciences, 2009 www.afs-journal.org
DOI: 10.1051/forest/2009088
Original article
Wood colour variation in sapwood and heartwood
of young trees of Tectona grandis and its relationship with plantation
characteristics, site, and decay resistance
Róger Moya
*
, Alexander B
errocal
Instituto Tecnológico de Costa Rica, Escuela de Ingeniería Forestal, Apartado 159-7050, Cartago, Costa Rica
(Received 8 January 2009; revised version 25 February 2009; accepted 2 July 2009)
Keyw ords:
CIELab colour system /
tropical wood /
Tectona grandis /
sapwood /
hardwood /
management plantation
Abstract
• Wood colour of Tectona grandis produced from fast-growth plantations is highly variable and the
causes of this variation are relatively unknown.
• With the purpose of understanding the colour variation, different fast-growth plantations were sam-
pled with different growth rates, tree ages, and sites.
• Wood colour was measured with a CIELab system, where three variables are estimated: coordinate
L
∗
for lightness, coordinate a
∗
defines redness and coordinate b
∗
defines yellowness.
• Results showed only a negative correlation between L
∗
and a
∗
. L
∗
and a
∗
were negatively and pos-
itively respectively correlated with pith distance in heartwood, but not for b
∗
. No correlations were
found between L
∗
and b
∗
in sapwood and plantation characteristics, while a
∗
was positively correlated
with age and height of tree and growth rate. In heartwood, tree age and diameter at breast height were
correlated with all colour parameters, but tree height and plantation density were correlated with a
∗
and b
∗
. Cluster site had correlation with L
∗
. Multiple correlation analysis showed that the heartwood
is increasing darker (L
∗
) and redder (a
∗
) when the trees are older and bigger. Correlation coefficient
shown that sapwood and heartwood with lighter colour (L
∗
) is less resistance to fungal attack, but
redness colour (a
∗
) increasing decay resistance.
Mots-clés :
CIELab /
bois tropicaux /
Tectona grandis /
aubier /
bois de cœur /
plantations
Résumé – Les variations de couleur dans l’aubier et le duramen de jeunes arbres de Tectona
grandis, en relation avec les caractéristiques des plantations, du site et de la durabilité.
• Il y a une grande variabilité de la couleur du bois de Tectona grandis produit à partir de plantations
à croissance rapide et les causes de ces variations sont relativement inconnues.
• Pour comprendre l’origine des variations de couleur nous avons échantillonné dans des plantations
à croissance rapide qui diffèrent entre elles en termes de vitesse de croissance, d’âge et de site.
• La couleur du bois a été mesurée avec le système CIELab qui permet la mesure de trois variables
colorimétriques : la luminance L
∗
allant du noir au blanc, a
∗
et b
∗
allant respectivement du vert au
rouge et du bleu au jaune.
• Les résultats montrent une corrélation négative entre L
∗
et a
∗
. Dans le bois le cœur il y a une
corrélation négative entre L
∗
et la distance à la moelle et une corrélation positive entre a
∗
et la distance
à la moelle : aucune corrélation n’apparaît pour b
∗
. Dans l’aubier, on ne trouve aucune corrélation
entre L
∗
et b
∗
et les caractéristiques des plantations. Cependant a
∗
est corrélé positivement avec l’âge,
la hauteur et la vitesse de croissance des arbres. Dans le bois de cœur, l’âge et le diamètre à 1,3 m
des arbres sont corrélés avec les trois coordonnées chromatiques mais la hauteur des arbres et la
densité de plantation sont corrélées avec a
∗
et b
∗
. Il y a une corrélation entre le site et L
∗
. On montre
que le bois de cœur est d’autant plus sombre et rouge que les arbres sont plus vieux et plus gros. Les
corrélations obtenues montrent que les bois d’aubier et de cœur qui sont les plus clairs résistent moins
bien aux attaques fongiques et que les bois de tendance plus rougeâtre ont une meilleure résistance
aux pourritures.
* Corresponding author: rmoya@itcr.ac.cr
Article published by EDP Sciences
Ann. For. Sci. 67 (2010) 109 R. Moya and A. Berrocal
1. INTRODUCTION
Wood colour, which differs widely among species as well
as within a single tree (Liu et al., 2005; Nishino et al., 1998),
is an important factor for determining specific uses such as fur-
niture and decorative veneers, both very important marketing
attributes (Mazet and Janin, 1990). One of the most accurate
and commonly used systems for measuring wood colour is the
CIELab colour system.
It has been used to measure colour variation and its rela-
tion to plant genetic sources (Sotela et al., 2008), effect of
drying on colour (Möttönen et al., 2002), relationship between
colour and decay resistance (Gierlinger at al., 2004), and effect
of thermal treatment on wood colour (Johansson and Morén,
2006).
Tectona grandis L.f. has been widely planted in all tropi-
cal regions including Latin America, Asia, Africa, and Ocea-
nia, in total covering approximately 6 million hectares (FAO,
2006). Teak is a premier hardwood valued for its durabil-
ity, aesthetics, and its golden brown colour (Thulasidas et al.,
2006). According to Bhat (1999), there are four colour groups
for T. grandis wood from native areas: (i) uniform golden
yellowbrown (typical) (ii) a darker yellowbrown (iii) uniform
grey-brown (produced from trees that grow no larger than the
pole stage) and (iv) light uniform yellow. Short-rotation trees
growing in forest plantations generally fetch a lower price in
the timber market because the wood is of inferior quality in
such attributes as colour, density, and mechanical properties
(Thulasidas et al., 2006).
In Costa Rica, large teak plantations have been established
and managed for fast growth and high timber productivity
(Pérez and Kanninen, 2005), with trees felled in a rotation pe-
riod of less than 20 y. The wood from these trees is usually
light brown with a large variation in colour. This results in a
reduced market value, and has led to its nickname “baby teak
wood”.
Bhat et al. (2005), Thulasidas et al. (2006) and Lukmandaru
and Takahashi (2008) report on the effects of tree age on teak
wood colour variation and its relationship to tree age and decay
resistance. However, wood colour is influenced by many other
factors, including site, stand conditions and management, ge-
netic source and age (Phelps et al., 1983). Most studies fo-
cused on heartwood with little consideration given to sap-
wood, although several studies of fast-grown T. grandis trees
have shown that a high sapwood fraction is present. Pérez and
Kanninen (2003) indicated that sapwood can reach 45% of the
total wood volume at 30 y, and is even greater in young trees.
Bhat (2000) also reported that young trees have a high propor-
tion of sapwood, with low natural durability.
To understand colour variation of fast-growing T. grandis,
we studied trees from three sites in Costa Rica, having dif-
ferent growth rates and ages. We investigated the influence of
growth rate, age, diameter at breast height (DBH), height, site
characteristics, and location of boards relative to the pith on
wood colour parameters of sapwood and heartwood. The rela-
tionship between wood colour and decay resistance was stud-
ied to examine the possibility of using colour as a parameter
for quality control.
Figure 1. Sawing pattern use for each stem section to obtain speci-
mens for wood colour.
2. MATERIALS AND METHODS
2.1. Study area and sample plantations
A total of 23 plantations of 7 to 15 y were selected in the north and
northwest regions of Costa Rica covering three cluster sites (Tab. I).
Annual precipitation was between 1 500 and 5 000 mm, with an aver-
age annual temperature of 20–28
◦
C. There was a long dry season be-
tween January and April in the northwest regions of clusters 2 and
3 and a short dry season in February and March in north regions of
cluster 1. The 23 sampled plantations were established by three dif-
ferent private companies along the study area. Stand density varied
between 160 to 580 trees/ha, depending on plantation age, manage-
ment, and site conditions (Tab. I). Plantation conditions were detailed
previously in Table I in Moya and Pérez (2008).
2.2. Sampled trees and wood sample preparation
Three trees from each plot were selected, taking into considera-
tion mean DBH, stem straightness, normality of branching, and ab-
sence of pests or diseases. The north side was marked on each tree
prior to harvesting. One 40-cm long log was cut at breast height from
each tree. These were stored in plastic bags until laboratory analysis.
A 3-cm-wide board was sawn through the pith in the north to south
direction from each log (Fig. 1). These boards were conditioned at
22
◦
C and 60% relative humidity for several weeks until reaching a
moisture content of 11–12%. The boards were then sawn into 2.5 cm
wide strips, with each strip labelled to indicate its radial position in
the stem (i.e., its relative distance from the pith) and whether it con-
sisted of sapwood or heartwood. Tangential surfaces were sanded to
reduce the effects of surface variation on colour, and after 20 h the
wood colour was measured.
109p2
Wood colour variation in trees of Tectona grandis Ann. For. Sci. 67 (2010) 109
Table I. Average dendrometric variables and site locations of each plantation evaluated in the present study.
Site Age Latitude Longitude Tree height Diameter breast Stand density
Clusters code (years) (N) (W) (m) height level (cm) (trees ha
−1
)
1
114N10
◦
45
42
W84
◦
27
15
25.80 25.60 264
214N10
◦
45
35
W84
◦
27
41
16.90 16.90 226
314N10
◦
48
43
W84
◦
26
20
22.10 25.30 264
414N10
◦
48
52
W84
◦
25
59
15.50 16.30 245
57N10
◦
51
21
W84
◦
29
54
18.07 19.90 396
67N10
◦
51
16
W84
◦
30
19
14.89 15.34 377
2
714N10
◦
59
03
W84
◦
45
04
19.10 22.30 188
814N10
◦
59
09
W84
◦
45
05
18.10 25.40 151
99N10
◦
58
46
W84
◦
44
45
16.13 19.37 318
3
10 11 N11
◦
05
24
W85
◦
27
36
17.70 21.30 300
11 11 N11
◦
04
48
W85
◦
27
00
15.90 18.90 440
12 10 N11
◦
06
36
W85
◦
28
12
18.00 22.50 440
13 10 N11
◦
06
00
W85
◦
28
12
15.00 18.90 520
4
14 8 N11
◦
12
00
W85
◦
35
24
13.10 17.80 580
15 8 N11
◦
12
00
W85
◦
36
00
16.50 21.10 500
16 10 N11
◦
11
24
W85
◦
37
48
14.10 18.70 460
17 10 N11
◦
11
24
W85
◦
37
12
19.10 25.10 320
18 15 N11
◦
09
36
W85
◦
41
24
22.50 26.50 300
19 15 N11
◦
09
00
W85
◦
41
24
21.60 24.20 320
5
20 13 N09
◦
50
49
W85
◦
10
52
23.20 25.40 172
21 13 N09
◦
50
18
W85
◦
11
02
23.30 27.40 160
22 15 N09
◦
49
19
W85
◦
14
40
22.00 23.20 328
23 15 N09
◦
49
56
W85
◦
14
32
22.10 24.20 338
2.3. Colour measurement
Wood colour was measured using a portable Miniscan XE plus
colorimeter (HUNTER LAB) at ambient temperature and humidity.
The colorimeter was recalibrated each time it was used, using a white
standard probe supplied by HUNTER LAB. The reflectance spectra
were recorded using the standardized CIEL
∗
a
∗
b
∗
chromaticity system
as a function of wavelength (BYK-Gardner, 2004). The measurement
was within the visible range of 400–700 nm at intervals of 10 nm
with a measuring aperture of 11 mm. For reflection readings, the ob-
server component was set at an angle of 90
◦
to the surface of the
specimen. The standard illuminant D65 (corresponding to daylight at
6 500 K) was used as the colour space measuring and computing pa-
rameter. The CIEL
∗
a
∗
b
∗
colour system estimates the value of three
variables: coordinate L
∗
for lightness, representing the position on
the black-white axis (L
∗
= 0 for black, L
∗
= 100 for white); coor-
dinate a
∗
for the position on the red-green axis (positive values for
red, negative values for green); and coordinate b
∗
for the position
on the yellow-blue axis (positive values for yellow, negative values
for blue) (Hunterlab 1995). Three measurements along the tangential
face were taken from each wood sample (Fig. 1) and average values
were obtained for L
∗
, a
∗
and b
∗
. A total of 394 samples were mea-
sured; 267 samples were heartwood and 127 were sapwood.
2.4. Decay resistance
Decay resistance specimens measuring 2.5 × 2.5 × 2.5cmwerecut
from the same locations where wood colour was measured (267 sam-
ples for heartwood, 127 samples for sapwood). The white-rot fungi
Trametes versicolor L. Fr. and Pycnoporus sanguineus (L.) Mer-
rill were used for testing natural decay resistance following ASTM
Standard D-2017-81 (ASTM, 2003). The relative resistance of each
test block to decay was measured as the percentage loss in oven-dry
weight during a 16-week exposure to the fungi. Although ASTM D-
2017-81 specifies that sample dimensions are 2.5 × 2.5 × 0.9cm,we
modified the procedure to use 2.5 × 2.5 × 2.5 cm samples.
2.5. Statistical analysis
The normality and the presence of outliers were examined for each
colour parameter. Regression analysis was used to determine the rela-
tionships of colour coordinates (L
∗
a
∗
b
∗
) in sapwood and heartwood,
and the effects of pith distance and decay resistance on colour vari-
ation. Pearson correlation coefficients were computed to show the
relationships among colour coordinates and plantation characteris-
tics (site, growth rate, age and height of tree, and DBH). Finally, we
used forward stepwise regression to determine the plantation vari-
ables having the greatest effects on wood colour. The colour coordi-
nates of all boards in each tree were averaged and used to compute
the correlation coefficients among colour and with plantation vari-
ables. SAS (SAS Institute Inc.) and STATISTICA 6.0 (Statsoft Inc.)
programs were used for the statistical computations.
3. RESULTS AND DISCUSSION
3.1. Wood colour
Table II shows the average colorimetry results for sapwood
and heartwood of T. grandis in CIEL
∗
a
∗
b
∗
colour systems.
Note that the values of colour coordinates are positive. All ob-
jects can have their colour described by the three variables L
∗
,
109p3
Ann. For. Sci. 67 (2010) 109 R. Moya and A. Berrocal
Table II. Colour parameters of Tectona grandis growing in Costa
Rica with CIELab system.
Wood L
∗
a
∗
b
∗
(lightness) (redness) (yellowness)
Sapwood 73.8 5.8 25.22
(N = 127) [63.62–80.90] [1.66–11.65] [19.44–32.62]
(3.45–4.66) (1.84–33.28) (2.95–11.70)
Heartwood 58.15 10.4 25.91
(N = 267) [46.78–76.56] [7.07–13.56] [20.06–30.11]
(5.66–9.67) (1.30–12.35) (2.21–8.54)
The values in square parenthesis represent minimum and maximum val-
ues and normal parenthesis standard deviations and variation coefficients.
a
∗
and b
∗
as described in the Materials and Methods. That is,
the colour composition of T. grandis wood can be described
using the combination of different tonalities of lightness, red-
ness, and yellowness. The values of L
∗
and b
∗
in the sapwood
and L
∗
, a
∗
and b
∗
in the heartwood were only small portions of
the possible ranges and had coefficients of variability (CV)of
less than 12.35% (Tab. II).
The lightness index (L
∗
) ranged from 63.62 to 80.90 in sap-
wood and from 46.78 to 75.56 in heartwood. The redness in-
dex (a
∗
) ranged from 1.66 to 11.65 and 7.07 to 13.56 for sap-
wood and heartwood, respectively; and yellowness (b
∗
) from
19.44 to 32.62 and from 20.06 to 30.11 in the heartwood and
sapwood, respectively (Tab. II). The variation of extractives or
chemical composition of lignin produced from different soil
properties can explain the wood colour variation of heartwood.
For example, redness (a
∗
) and lightness (L
∗
) are correlated
with extractive content, while yellowness is primarily related
to the photochemistry of the major wood components, espe-
cially lignin (Gierlinger et al., 2004).
In sapwood, the a
∗
values had the greatest variability com-
pared with the possible range, with a CV of 33.28% (Tab. II).
As expected, the colour composition of heartwood and sap-
wood are different. Heartwood colour has lower values of L
∗
and higher values of a
∗
compared to sapwood (Tab. II). The
change in colour from sapwood to heartwood is due to the
synthesis and accumulation of extractives during heartwood
formation. Variation in colour within heartwood is due to ox-
idation and polymerization reactions that take place as wood
ages (Gierlinger et al., 2004).
The wood colour variation that we found in T. grandis is
considered large for end users (Bhat, 1999). The variation in
the colour space of a three-dimensional model is the quadratic
summation of differences in each coordinate (Gonnet, 1993).
Mazet and Janin (1990) report that oak veneer samples eval-
uated by 90 French and Italian assessors from woodworking
industries consider that a difference of over two units in the
value of [(L
∗
− L
∗
)
2
+ (a
∗
− a
∗
)
2
+ (b
∗
− b
∗
)
2
] is distinguishable
to the human eye. For agricultural or horticultural applications
this difference varied from 1.0 to 3.0 (Voss and Hale, 1998).
Therefore, a difference in two points in different samples of
T. grandis in all coordinates of colour systems will produce a
difference distinguishable to the human eye.
The L
∗
, a
∗
,andb
∗
values obtained in wood from fast-growth
plantation T. grandis in Costa Rica are different from the re-
sults found in other studies. For example, Thulasidas et al.
(2006) reported average values of 56.34, 6.85, and 23.44 for
L
∗
, a
∗
,andb
∗
, respectively, for heartwood from trees growing
in plantations in India. The T. grandis heartwood from trees
growing in Costa Rican is lighter and redder than wood from
India (Tab. II). However, this comparison must be interpreted
with caution because genetic factors, tree age, climate and soil
fertility are different for India and Costa Rica, and different
colour equipment was used in each study. Our study used a
colorimeter, whereas Thulasidas et al. (2006) used a UV spec-
trophotometer, so equipment differences may be responsible
for the differences in wood colour determination. Lukmandaru
and Takahashi (2008) studied T. grandis trees of different ages
on Java, and found ranges wider than ours. L
∗
ranged from
75–77 and 54–60, for sapwood and heartwood, respectively,
a
∗
ranged from 2–3 and 4–6 in sapwood and heartwood, re-
spectively, and b
∗
ranged from 22–25 and 24–26 in sapwood
and heartwood, respectively. These ranges are narrower than
those for Costa Rican T. grandis (Tab. II).
3.2. Relation between wood colour coordinates
Figure 2 shows the relationships among the colour param-
eters defining the heartwood and sapwood measurements. A
significant correlation was found only between L
∗
and a
∗
in
both sapwood and heartwood. A low coefficient of determina-
tion was found in both, R
2
= 0.38 for heartwood and R
2
= 0.43
for sapwood (Fig. 2a). No significant correlation was found
between L
∗
and b
∗
(Fig. 2b) and b
∗
and a
∗
(Fig. 2c). These
results show that the variation in wood colour of T. grandis
is produced by an inverse variation between L
∗
and a
∗
coordi-
nates, lightness and redness, respectively. Nishino et al. (1998)
measured the correlations between different colour parameters
of many tropical species from Guiana, and their results agree
with our findings for T. grandis. They found significant rela-
tionships between L
∗
and a
∗
, but not between a
∗
and b
∗
.In
Fagus sylvatica, Liu et al. (2005) found that the parameters of
the CIEL
∗
a
∗
b
∗
colour system were significantly correlated (L
∗
with a
∗
, L
∗
with b
∗
,anda
∗
with b
∗
), but in T. grandis the only
significant correlation was with a
∗
.
3.3. Wood colour variation with distance from the pith
The colour coordinates L
∗
and a
∗
were statistically corre-
lated (α = 0.05) with distance from pith for heartwood, but not
for sapwood (Fig. 3). However, low but significant correlation
coefficients were found in heartwood, (R = −0.36) for the re-
lationships of L
∗
with distance from pith (Fig. 3a) and a
∗
with
distance from pith (R = 0.36) (Fig. 3b). For coordinate b
∗
,no
significant correlations were found (Fig. 3c). In summary, the
heartwood colour is lightest with lowest redness near the pith,
becoming darker with increase in redness as distance from pith
increases.
109p4
